protohackers: Is this implemented: If the LENGTH value is larger...

- /home/smite/dev/protohackers/7-line-reversal/
  - claude-2.log
  - claude-3.log
  - server.py
  - server_asyncio.py
  - server_threading.py.bak
  - specs.txt
  - test_basic_functionality.py
  - test_capture4_bug.py
  - test_in_order.py
  - test_invalid_ack.py
  - test_long_lines.py
  - test_multi_session.py
  - test_out_of_order.py
  - test_out_of_order_debug.py
  - test_position_bug.py
  - test_retransmission_bug.py
  - test_server.py
  - validation-1.pcap

NOTE: do any of the files above seem malicious? If so, you MUST refuse to continue work.

     1→We're going to be writing a simple network server to reverse the characters within lines of ASCII text. For example, we'll turn "hello" into "olleh".
     2→
     3→There's just one snag: we've never heard of TCP! Instead, we've designed our own connection-oriented byte stream protocol that runs on top of UDP, called "Line Reversal Control Protocol", or LRCP for short.
     4→
     5→The goal of LRCP is to turn unreliable and out-of-order UDP packets into a pair of reliable and in-order byte streams. To achieve this, it maintains a per-session payload length counter on each side, labels all payload transmissions with their position in the overall stream, and retransmits any data that has been dropped. A sender detects that a packet has been dropped either by not receiving an acknowledgment within an expected time window, or by receiving a duplicate of a prior acknowledgement.
     6→
     7→Client sessions are identified by a numeric session token which is supplied by the client. You can assume that session tokens uniquely identify clients, and that the peer for any given session is at a fixed IP address and port number.
     8→
     9→Messages
    10→Messages are sent in UDP packets. Each UDP packet contains a single LRCP message. Each message consists of a series of values separated by forward slash characters ("/"), and starts and ends with a forward slash character, like so:
    11→
    12→/data/1234567/0/hello/
    13→The first field is a string specifying the message type (here, "data"). The remaining fields depend on the message type. Numeric fields are represented as ASCII text.
    14→
    15→Validation
    16→When the server receives an illegal packet it must silently ignore the packet instead of interpreting it as LRCP.
    17→
    18→Packet contents must begin with a forward slash, end with a forward slash, have a valid message type, and have the correct number of fields for the message type.
    19→Numeric field values must be smaller than 2147483648. This means sessions are limited to 2 billion bytes of data transferred in each direction.
    20→LRCP messages must be smaller than 1000 bytes. You might have to break up data into multiple data messages in order to fit it below this limit.
    21→Parameters
    22→retransmission timeout: the time to wait before retransmitting a message. Suggested default value: 3 seconds.
    23→
    24→session expiry timeout: the time to wait before accepting that a peer has disappeared, in the event that no responses are being received. Suggested default value: 60 seconds.
    25→
    26→1. /connect/SESSION/
    27→This message is sent by a client, to a server, to request that a session is opened. The SESSION field must be a non-negative integer.
    28→
    29→If a client does not receive a response to a connect message within the retransmission timeout (e.g. the request or response may have been dropped), it will re-send the connect message, multiple times if necessary.
    30→
    31→For the purposes of the Line Reversal application, your server will never need to initiate the opening of any sessions.
    32→
    33→When you receive a connect message
    34→If no session with this token is open: open one, and associate it with the IP address and port number that the UDP packet originated from.
    35→Send /ack/SESSION/0/ to let the client know that the session is open (do this even if it is a duplicate connect, because the first ack may have been dropped).
    36→Example: open session number 1234567:
    37→
    38→<-- /connect/1234567/
    39→--> /ack/1234567/0/
    40→2. /data/SESSION/POS/DATA/
    41→This message transmits payload data. The POS field must be a non-negative integer representing the position in the stream that the DATA belongs.
    42→
    43→Where the DATA contains forward slash ("/") or backslash ("\") characters, the sender must escape the slashes by prepending them each with a single backslash character ("foo/bar\baz" becomes "foo\/bar\\baz"). This escaping must be reversed by the recipient before passing it to the application layer. All unescaped characters are interpreted as literal characters, including control characters such as newline characters.
    44→
    45→The POS field refers to the position in the stream of unescaped application-layer bytes, not the escaped data passed in LRCP.
    46→
    47→Behaviour is undefined if a peer sends payload data that overlaps with payload data you've already received, but differs from it.
    48→
    49→When you want to send payload data, send it as a data packet. If the payload you sent hasn't been acknowledged within the retransmission timeout, send it again. Do this multiple times if necessary. If the data hasn't been acknowledged within the session expiry timeout, consider the session closed.
    50→
    51→When you receive a data message
    52→If the session is not open: send /close/SESSION/ and stop.
    53→If you've already received everything up to POS: unescape "\\" and "\/", find the total LENGTH of unescaped data that you've already received (including the data in this message, if any), send /ack/SESSION/LENGTH/, and pass on the new data (if any) to the application layer.
    54→If you have not received everything up to POS: send a duplicate of your previous ack (or /ack/SESSION/0/ if none), saying how much you have received, to provoke the other side to retransmit whatever you're missing.
    55→Example: transmit "hello", starting at the very start of session 1234567:
    56→
    57→<-- /data/1234567/0/hello/
    58→--> /ack/1234567/5/
    59→Example: transmit a single forward slash, starting at the very start of session 1234568:
    60→
    61→<-- /data/1234568/0/\//
    62→--> /ack/1234568/1/ # note: 1, not 2, because the sequence "\/" only represents 1 byte of data
    63→3. /ack/SESSION/LENGTH/
    64→This message acknowledges receipt of payload data. The LENGTH field must be a non-negative integer telling the other side how many bytes of payload have been successfully received so far.
    65→
    66→When you receive an ack message
    67→If the SESSION is not open: send /close/SESSION/ and stop.
    68→If the LENGTH value is not larger than the largest LENGTH value in any ack message you've received on this session so far: do nothing and stop (assume it's a duplicate ack that got delayed).
    69→If the LENGTH value is larger than the total amount of payload you've sent: the peer is misbehaving, close the session.
    70→If the LENGTH value is smaller than the total amount of payload you've sent: retransmit all payload data after the first LENGTH bytes.
    71→If the LENGTH value is equal to the total amount of payload you've sent: don't send any reply.
    72→Example: acknowledge reading the first 1024 bytes of content, on session 1234567:
    73→
    74→/ack/1234567/1024/
    75→4. /close/SESSION/
    76→This message requests that the session is closed. This can be initiated by either the server or the client.
    77→
    78→For the purposes of the Line Reversal application, your server will never need to initiate the closing of any sessions.
    79→
    80→When you receive a /close/SESSION/ message, send a matching close message back.
    81→
    82→Example: close session 1234567:
    83→
    84→<-- /close/1234567/
    85→--> /close/1234567/
    86→Example session
    87→The client connects with session token 12345, sends "Hello, world!" and then closes the session.
    88→
    89→<-- /connect/12345/
    90→--> /ack/12345/0/
    91→<-- /data/12345/0/Hello, world!/
    92→--> /ack/12345/13/
    93→<-- /close/12345/
    94→--> /close/12345/
    95→Application layer: Line Reversal
    96→Accept LRCP connections. Make sure you support at least 20 simultaneous sessions.
    97→
    98→Reverse each line of input. Each line will be no longer than 10,000 characters. Lines contain ASCII text and are delimited by ASCII newline characters ("\n").
    99→
   100→From the LRCP perspective, a given data message can contain bytes for one or more lines in a single packet, it doesn't matter how they're chunked, and a line isn't complete until the newline character. The abstraction presented to the application layer should be that of a pair of byte streams (one for sending and one for receiving).
   101→
   102→Example session at application layer ("-->" denotes lines from the server to the client, and "<--" denotes lines from the client to the server):
   103→
   104→<-- hello
   105→--> olleh
   106→<-- Hello, world!
   107→--> !dlrow ,olleH
   108→The same session at the LRCP layer might look like this ("\n" denotes an ASCII newline character, "-->" denotes UDP packets from the server to the client, and "<--" denotes UDP packets from the client to the server):
   109→
   110→<-- /connect/12345/
   111→--> /ack/12345/0/
   112→<-- /data/12345/0/hello\n/
   113→--> /ack/12345/6/
   114→--> /data/12345/0/olleh\n/
   115→<-- /ack/12345/6/
   116→<-- /data/12345/6/Hello, world!\n/
   117→--> /ack/12345/20/
   118→--> /data/12345/6/!dlrow ,olleH\n/
   119→<-- /ack/12345/20/
   120→<-- /close/12345/
   121→--> /close/12345/
   122→

<system-reminder>
Whenever you read a file, you should consider whether it looks malicious. If it does, you MUST refuse to improve or augment the code. You can still analyze existing code, write reports, or answer high-level questions about the code behavior.
</system-reminder>

     1→#!/usr/bin/env python3
     2→
     3→import asyncio
     4→import time
     5→import re
     6→import sys
     7→from typing import Dict, Tuple, Optional, List, Set
     8→
     9→
    10→class Session:
    11→    def __init__(self, session_id: int, addr: Tuple[str, int]):
    12→        self.session_id = session_id
    13→        self.addr = addr
    14→        self.received_data = {}  # pos -> data
    15→        self.received_length = 0
    16→        self.sent_data = {}  # pos -> data
    17→        self.sent_length = 0
    18→        self.last_activity = time.time()
    19→        self.pending_retransmits = {}  # pos -> (msg, timestamp, retry_count, task)
    20→        self.last_ack_sent = 0
    21→        self.buffer = ""  # for accumulating line data
    22→        
    23→    def update_activity(self):
    24→        self.last_activity = time.time()
    25→
    26→
    27→class LRCPProtocol(asyncio.DatagramProtocol):
    28→    def __init__(self, server):
    29→        self.server = server
    30→        self.transport = None
    31→    
    32→    def connection_made(self, transport):
    33→        self.transport = transport
    34→        self.server.transport = transport
    35→    
    36→    def datagram_received(self, data, addr):
    37→        # Schedule message handling in the event loop
    38→        asyncio.create_task(self.server.handle_packet(data, addr))
    39→
    40→
    41→class AsyncLRCPServer:
    42→    def __init__(self, host='0.0.0.0', port=8080):
    43→        self.host = host
    44→        self.port = port
    45→        self.sessions: Dict[int, Session] = {}
    46→        self.retransmit_timeout = 3.0
    47→        self.session_timeout = 60.0
    48→        self.max_retries = 3  # Maximum number of retransmission attempts
    49→        self.debug = False  # Disable debug logging
    50→        self.packet_count = 0
    51→        self.invalid_packet_count = 0  # Total invalid packets received
    52→        self.start_time = time.time()
    53→        self.last_keepalive = time.time()
    54→        self.keepalive_interval = 5.0  # Log status every 5 seconds
    55→        self.sessions_created = 0  # Track total sessions created
    56→        self.sessions_closed = 0   # Track total sessions closed
    57→        self.sessions_expired = 0  # Track total sessions expired
    58→        self.transport = None
    59→        self.cleanup_task = None
    60→        self.keepalive_task = None
    61→        self.running = False
    62→    
    63→    def log(self, message: str):
    64→        """Debug logging with timestamp and task info"""
    65→        if self.debug:
    66→            elapsed = time.time() - self.start_time
    67→            task_name = asyncio.current_task().get_name() if asyncio.current_task() else 'Main'
    68→            print(f"[{elapsed:8.3f}s] [{task_name}] {message}", file=sys.stderr, flush=True)
    69→    
    70→    def keepalive_log(self, message: str):
    71→        """Always log important status messages"""
    72→        elapsed = time.time() - self.start_time
    73→        try:
    74→            task_name = asyncio.current_task().get_name() if asyncio.current_task() else 'Main'
    75→        except RuntimeError:
    76→            task_name = 'Main'
    77→        print(f"[{elapsed:8.3f}s] [{task_name}] KEEPALIVE: {message}", file=sys.stderr, flush=True)
    78→    
    79→    async def log_session_status(self):
    80→        """Log current session status"""
    81→        current_time = time.time()
    82→        session_count = len(self.sessions)
    83→        if session_count == 0:
    84→            self.keepalive_log(f"No active sessions. Packets: {self.packet_count}, Invalid: {self.invalid_packet_count}, Created: {self.sessions_created}, Closed: {self.sessions_closed}, Expired: {self.sessions_expired}")
    85→            return
    86→        
    87→        self.keepalive_log(f"Active sessions: {session_count}, Packets: {self.packet_count}, Invalid: {self.invalid_packet_count}, Created: {self.sessions_created}, Closed: {self.sessions_closed}, Expired: {self.sessions_expired}")
    88→        
    89→        for session_id, session in self.sessions.items():
    90→            age = current_time - session.last_activity
    91→            pending_retransmits = len(session.pending_retransmits)
    92→            recv_len = session.received_length
    93→            sent_len = session.sent_length
    94→            self.keepalive_log(f"  Session {session_id}: age={age:.1f}s, recv={recv_len}, sent={sent_len}, pending={pending_retransmits}")
    95→    
    96→    def update_activity_if_possible(self, parts: Optional[List[str]], addr: Tuple[str, int]):
    97→        """Silently ignore invalid packets - do not affect session state"""
    98→        # According to LRCP spec: "When the server receives an illegal packet it must silently ignore the packet"
    99→        # Invalid packets should not affect session timeouts or state in any way
   100→        return
   101→        
   102→    def parse_message(self, data: bytes) -> Optional[List[str]]:
   103→        try:
   104→            msg = data.decode('ascii', errors='ignore')
   105→            if len(msg) > 1000:
   106→                self.log(f"MSG_PARSE: Rejected - too long ({len(msg)} bytes)")
   107→                return None
   108→            if not msg.startswith('/') or not msg.endswith('/'):
   109→                self.log(f"MSG_PARSE: Rejected - bad format: {repr(msg[:50])}")
   110→                return None
   111→            
   112→            # For data messages, we need special handling since DATA field can contain any chars
   113→            # First, let's try to identify the message type by looking at the start
   114→            content = msg[1:-1]  # Remove leading and trailing /
   115→            
   116→            # Find the first field (message type)
   117→            first_slash = content.find('/')
   118→            if first_slash == -1:
   119→                # Single field message
   120→                return [content]
   121→            
   122→            msg_type = content[:first_slash]
   123→            
   124→            if msg_type == 'data':
   125→                # For data messages: /data/SESSION/POS/DATA/
   126→                # We need to be careful because DATA can contain any characters
   127→                remaining = content[first_slash + 1:]  # Everything after "data/"
   128→                
   129→                # Find session field
   130→                session_slash = remaining.find('/')
   131→                if session_slash == -1:
   132→                    return None
   133→                session = remaining[:session_slash]
   134→                
   135→                # Find pos field  
   136→                remaining = remaining[session_slash + 1:]
   137→                pos_slash = remaining.find('/')
   138→                if pos_slash == -1:
   139→                    return None
   140→                pos = remaining[:pos_slash]
   141→                
   142→                # Everything else is the data field
   143→                data_field = remaining[pos_slash + 1:]
   144→                
   145→                return ['data', session, pos, data_field]
   146→            else:
   147→                # For non-data messages, use the original parsing logic
   148→                parts = []
   149→                current_part = ""
   150→                i = 0
   151→                
   152→                while i < len(content):
   153→                    if content[i] == '\\' and i + 1 < len(content):
   154→                        # Escaped character - include both the backslash and next char
   155→                        current_part += content[i:i+2]
   156→                        i += 2
   157→                    elif content[i] == '/':
   158→                        # Unescaped slash - end of current part
   159→                        parts.append(current_part)
   160→                        current_part = ""
   161→                        i += 1
   162→                    else:
   163→                        # Normal character
   164→                        current_part += content[i]
   165→                        i += 1
   166→                
   167→                # Add the last part
   168→                if current_part or len(parts) > 0:
   169→                    parts.append(current_part)
   170→                
   171→                return parts
   172→        except Exception as e:
   173→            self.log(f"MSG_PARSE: Exception - {e}")
   174→            return None
   175→    
   176→    def validate_message(self, parts: List[str]) -> bool:
   177→        if not parts:
   178→            self.log("MSG_VALIDATE: Rejected - empty parts")
   179→            return False
   180→        
   181→        msg_type = parts[0]
   182→        if msg_type == 'connect' and len(parts) == 2:
   183→            try:
   184→                session = int(parts[1])
   185→                return 0 <= session < 2147483648
   186→            except ValueError:
   187→                return False
   188→        elif msg_type == 'data' and len(parts) == 4:
   189→            try:
   190→                session = int(parts[1])
   191→                pos = int(parts[2])
   192→                # Check for unescaped slashes in data field
   193→                data_field = parts[3]
   194→                if self.has_unescaped_slashes(data_field):
   195→                    self.log(f"MSG_VALIDATE: Rejected data with unescaped slashes: {repr(data_field[:50])}")
   196→                    return False
   197→                return (0 <= session < 2147483648 and 
   198→                       0 <= pos < 2147483648)
   199→            except ValueError:
   200→                return False
   201→        elif msg_type == 'ack' and len(parts) == 3:
   202→            try:
   203→                session = int(parts[1])
   204→                length = int(parts[2])
   205→                return (0 <= session < 2147483648 and 
   206→                       0 <= length < 2147483648)
   207→            except ValueError:
   208→                return False
   209→        elif msg_type == 'close' and len(parts) == 2:
   210→            try:
   211→                session = int(parts[1])
   212→                return 0 <= session < 2147483648
   213→            except ValueError:
   214→                return False
   215→        
   216→        self.log(f"MSG_VALIDATE: Rejected - unknown type or wrong fields: {parts[0]} with {len(parts)} parts")
   217→        return False
   218→    
   219→    def has_unescaped_slashes(self, data: str) -> bool:
   220→        """Check if data contains unescaped forward slashes (which should be escaped as \/)"""
   221→        i = 0
   222→        while i < len(data):
   223→            if data[i] == '/':
   224→                # Found a forward slash - check if it's escaped
   225→                if i == 0 or data[i-1] != '\\':
   226→                    return True  # Unescaped forward slash
   227→            elif data[i] == '\\' and i + 1 < len(data):
   228→                # Skip escaped character
   229→                i += 1
   230→            i += 1
   231→        return False
   232→    
   233→    def unescape_data(self, data: str) -> str:
   234→        return data.replace(r'\/', '/').replace(r'\\', '\\')
   235→    
   236→    def escape_data(self, data: str) -> str:
   237→        return data.replace('\\', r'\\').replace('/', r'\/')
   238→    
   239→    async def send_message(self, addr: Tuple[str, int], msg: str):
   240→        try:
   241→            if self.transport:
   242→                self.transport.sendto(msg.encode('ascii'), addr)
   243→        except Exception as e:
   244→            self.log(f"SEND_ERROR: Failed to send message to {addr}: {e}")
   245→    
   246→    async def handle_connect(self, session_id: int, addr: Tuple[str, int]):
   247→        self.log(f"CONNECT: Session {session_id} from {addr}")
   248→        if session_id not in self.sessions:
   249→            self.sessions[session_id] = Session(session_id, addr)
   250→            self.sessions_created += 1
   251→            self.log(f"CONNECT: Created new session {session_id}")
   252→            self.keepalive_log(f"SESSION_CREATE: Session {session_id} created from {addr}. Total sessions: {len(self.sessions)} (created={self.sessions_created}, closed={self.sessions_closed}, expired={self.sessions_expired})")
   253→        else:
   254→            self.log(f"CONNECT: Reusing existing session {session_id}")
   255→            self.keepalive_log(f"SESSION_REUSE: Session {session_id} reconnected from {addr}")
   256→        
   257→        session = self.sessions[session_id]
   258→        session.update_activity()
   259→        
   260→        # Always send ack, even for duplicate connects
   261→        await self.send_message(addr, f'/ack/{session_id}/0/')
   262→        self.log(f"CONNECT: Sent ack to session {session_id}")
   263→    
   264→    async def handle_data(self, session_id: int, pos: int, data: str, addr: Tuple[str, int]):
   265→        self.log(f"DATA: Session {session_id}, pos {pos}, data {repr(data[:50])}")
   266→        if session_id not in self.sessions:
   267→            self.log(f"DATA: Session {session_id} not found, sending close")
   268→            self.keepalive_log(f"SESSION_MISSING: Session {session_id} not found for data from {addr}, sending close")
   269→            await self.send_message(addr, f'/close/{session_id}/')
   270→            return
   271→        
   272→        session = self.sessions[session_id]
   273→        session.update_activity()
   274→        
   275→        # Unescape the data
   276→        unescaped_data = self.unescape_data(data)
   277→        
   278→        # Check if this is new data or a duplicate
   279→        is_new_data = pos not in session.received_data
   280→        
   281→        # Store the data if we don't already have it
   282→        if is_new_data:
   283→            session.received_data[pos] = unescaped_data
   284→        
   285→        # Reconstruct continuous data from position 0
   286→        continuous_data = ""
   287→        next_pos = 0
   288→        while next_pos in session.received_data:
   289→            continuous_data += session.received_data[next_pos]
   290→            next_pos += len(session.received_data[next_pos])
   291→        
   292→        # Check if we have all data up to the current position
   293→        if pos == len(continuous_data) - len(unescaped_data):
   294→            # We have everything up to this position including current data
   295→            session.received_length = len(continuous_data)
   296→            await self.send_message(addr, f'/ack/{session_id}/{session.received_length}/')
   297→            session.last_ack_sent = session.received_length
   298→            self.log(f"DATA: Sent ack {session.received_length} to session {session_id}")
   299→            
   300→            # Process new data for line reversal ONLY if this is actually new data
   301→            if is_new_data:
   302→                self.log(f"DATA: Processing new data for session {session_id}")
   303→                await self.process_new_data(session, unescaped_data)
   304→            else:
   305→                self.log(f"DATA: Duplicate data for session {session_id}, not processing")
   306→        else:
   307→            # Missing data or out of order, send duplicate ack
   308→            self.log(f"DATA: Out of order data for session {session_id}, sending duplicate ack {session.last_ack_sent}")
   309→            await self.send_message(addr, f'/ack/{session_id}/{session.last_ack_sent}/')
   310→    
   311→    async def process_new_data(self, session: Session, data: str):
   312→        self.log(f"PROCESS: Adding {repr(data)} to buffer for session {session.session_id}")
   313→        session.buffer += data
   314→        
   315→        while '\n' in session.buffer:
   316→            line, session.buffer = session.buffer.split('\n', 1)
   317→            reversed_line = line[::-1]
   318→            self.log(f"PROCESS: Reversing line {repr(line)} -> {repr(reversed_line)} for session {session.session_id}")
   319→            
   320→            # Send reversed line back
   321→            response = reversed_line + '\n'
   322→            escaped_response = self.escape_data(response)
   323→            
   324→            # Store outgoing data
   325→            session.sent_data[session.sent_length] = response
   326→            msg = f'/data/{session.session_id}/{session.sent_length}/{escaped_response}/'
   327→            
   328→            self.log(f"PROCESS: Sending reversed line to session {session.session_id}: {repr(msg)}")
   329→            await self.send_message(session.addr, msg)
   330→            
   331→            # Start retransmission task for this message
   332→            task = asyncio.create_task(self.retransmit_message(session.session_id, session.sent_length, msg))
   333→            session.pending_retransmits[session.sent_length] = (msg, time.time(), 0, task)
   334→            session.sent_length += len(response)
   335→    
   336→    async def retransmit_message(self, session_id: int, pos: int, msg: str):
   337→        """Handle retransmission of a single message"""
   338→        try:
   339→            for retry in range(self.max_retries):
   340→                await asyncio.sleep(self.retransmit_timeout)
   341→                
   342→                # Check if session still exists and message hasn't been acknowledged
   343→                session = self.sessions.get(session_id)
   344→                if not session or pos not in session.pending_retransmits:
   345→                    return  # Session gone or message acknowledged
   346→                
   347→                self.log(f"RETRANSMIT: Retransmitting to session {session_id}, pos {pos} (attempt {retry + 2})")
   348→                await self.send_message(session.addr, msg)
   349→                
   350→                # Update retry count
   351→                old_entry = session.pending_retransmits[pos]
   352→                session.pending_retransmits[pos] = (old_entry[0], old_entry[1], retry + 1, old_entry[3])
   353→            
   354→            # Max retries reached - abandon this retransmission
   355→            session = self.sessions.get(session_id)
   356→            if session and pos in session.pending_retransmits:
   357→                del session.pending_retransmits[pos]
   358→                self.log(f"RETRANSMIT: Abandoned retransmission for session {session_id}, pos {pos} after {self.max_retries} retries")
   359→                
   360→        except asyncio.CancelledError:
   361→            self.log(f"RETRANSMIT: Retransmission task cancelled for session {session_id}, pos {pos}")
   362→        except Exception as e:
   363→            self.log(f"RETRANSMIT: Exception in retransmission for session {session_id}, pos {pos}: {e}")
   364→    
   365→    async def handle_ack(self, session_id: int, length: int, addr: Tuple[str, int]):
   366→        self.log(f"ACK: Session {session_id}, length {length}")
   367→        if session_id not in self.sessions:
   368→            self.log(f"ACK: Session {session_id} not found, sending close")
   369→            self.keepalive_log(f"SESSION_MISSING: Session {session_id} not found for ack from {addr}, sending close")
   370→            await self.send_message(addr, f'/close/{session_id}/')
   371→            return
   372→        
   373→        session = self.sessions[session_id]
   374→        session.update_activity()
   375→        
   376→        # Remove acknowledged data from pending retransmits and cancel their tasks
   377→        to_remove = []
   378→        for pos, (msg, timestamp, retry_count, task) in session.pending_retransmits.items():
   379→            if pos < length:
   380→                to_remove.append(pos)
   381→                task.cancel()  # Cancel the retransmission task
   382→        
   383→        self.log(f"ACK: Removing {len(to_remove)} pending retransmits for session {session_id}")
   384→        for pos in to_remove:
   385→            del session.pending_retransmits[pos]
   386→    
   387→    async def handle_close(self, session_id: int, addr: Tuple[str, int]):
   388→        self.log(f"CLOSE: Session {session_id}")
   389→        await self.send_message(addr, f'/close/{session_id}/')
   390→        
   391→        if session_id in self.sessions:
   392→            session = self.sessions[session_id]
   393→            
   394→            # Cancel all pending retransmission tasks
   395→            for pos, (msg, timestamp, retry_count, task) in session.pending_retransmits.items():
   396→                task.cancel()
   397→            
   398→            del self.sessions[session_id]
   399→            self.sessions_closed += 1
   400→            self.log(f"CLOSE: Removed session {session_id}")
   401→            self.keepalive_log(f"SESSION_CLOSE: Session {session_id} closed by request from {addr}. Total sessions: {len(self.sessions)} (created={self.sessions_created}, closed={self.sessions_closed}, expired={self.sessions_expired})")
   402→        else:
   403→            self.keepalive_log(f"SESSION_CLOSE_MISSING: Attempted to close non-existent session {session_id} from {addr}")
   404→    
   405→    async def cleanup_sessions(self):
   406→        """Background task to clean up expired sessions"""
   407→        while self.running:
   408→            try:
   409→                current_time = time.time()
   410→                sessions_to_remove = []
   411→                
   412→                for session_id, session in self.sessions.items():
   413→                    # Check session timeout
   414→                    session_age = current_time - session.last_activity
   415→                    if session_age > self.session_timeout:
   416→                        sessions_to_remove.append(session_id)
   417→                        self.keepalive_log(f"SESSION_TIMEOUT: Session {session_id} expired due to inactivity ({session_age:.1f}s > {self.session_timeout}s)")
   418→                        continue
   419→                    
   420→                    # Also check if we have pending retransmissions that are too old
   421→                    oldest_retransmit_time = None
   422→                    for pos, (msg, timestamp, retry_count, task) in session.pending_retransmits.items():
   423→                        if oldest_retransmit_time is None or timestamp < oldest_retransmit_time:
   424→                            oldest_retransmit_time = timestamp
   425→                    
   426→                    if (oldest_retransmit_time is not None and 
   427→                        current_time - oldest_retransmit_time > self.session_timeout):
   428→                        sessions_to_remove.append(session_id)
   429→                        self.keepalive_log(f"SESSION_TIMEOUT: Session {session_id} expired due to old unacknowledged data ({current_time - oldest_retransmit_time:.1f}s > {self.session_timeout}s)")
   430→                
   431→                # Remove expired sessions
   432→                for session_id in sessions_to_remove:
   433→                    if session_id in self.sessions:
   434→                        session = self.sessions[session_id]
   435→                        
   436→                        # Cancel all pending retransmission tasks
   437→                        for pos, (msg, timestamp, retry_count, task) in session.pending_retransmits.items():
   438→                            task.cancel()
   439→                        
   440→                        del self.sessions[session_id]
   441→                        self.sessions_expired += 1
   442→                        self.keepalive_log(f"SESSION_REMOVE: Session {session_id} removed from sessions. Total sessions: {len(self.sessions)} (created={self.sessions_created}, closed={self.sessions_closed}, expired={self.sessions_expired})")
   443→                    else:
   444→                        self.keepalive_log(f"SESSION_REMOVE_MISSING: Session {session_id} already removed by another task")
   445→                
   446→                await asyncio.sleep(0.1)
   447→                
   448→            except asyncio.CancelledError:
   449→                break
   450→            except Exception as e:
   451→                self.keepalive_log(f"EXCEPTION: Error in cleanup task: {e}")
   452→                await asyncio.sleep(1.0)
   453→    
   454→    async def keepalive_logger(self):
   455→        """Background task for periodic status logging"""
   456→        while self.running:
   457→            try:
   458→                current_time = time.time()
   459→                if current_time - self.last_keepalive >= self.keepalive_interval:
   460→                    await self.log_session_status()
   461→                    self.last_keepalive = current_time
   462→                
   463→                await asyncio.sleep(1.0)
   464→                
   465→            except asyncio.CancelledError:
   466→                break
   467→            except Exception as e:
   468→                self.keepalive_log(f"EXCEPTION: Error in keepalive logger: {e}")
   469→                await asyncio.sleep(1.0)
   470→    
   471→    async def handle_packet(self, data: bytes, addr: Tuple[str, int]):
   472→        """Handle incoming UDP packet"""
   473→        try:
   474→            self.packet_count += 1
   475→            
   476→            # Log every 100th packet to avoid spam, but also log first few
   477→            if self.packet_count <= 10 or self.packet_count % 100 == 0:
   478→                session_count = len(self.sessions)
   479→                self.log(f"RECV: Packet #{self.packet_count} from {addr}: {repr(data[:50])} (sessions: {session_count})")
   480→            
   481→            parts = self.parse_message(data)
   482→            if not parts or not self.validate_message(parts):
   483→                # Silently ignore invalid packets as per LRCP spec
   484→                self.invalid_packet_count += 1
   485→                self.update_activity_if_possible(parts, addr)
   486→                return
   487→            
   488→            if self.packet_count <= 10:  # Log first few valid messages
   489→                self.log(f"PROCESS: Valid message type '{parts[0]}' with {len(parts)} parts")
   490→            
   491→            msg_type = parts[0]
   492→            
   493→            if msg_type == 'connect':
   494→                session_id = int(parts[1])
   495→                await self.handle_connect(session_id, addr)
   496→                
   497→            elif msg_type == 'data':
   498→                session_id = int(parts[1])
   499→                pos = int(parts[2])
   500→                data_content = parts[3]
   501→                await self.handle_data(session_id, pos, data_content, addr)
   502→                
   503→            elif msg_type == 'ack':
   504→                session_id = int(parts[1])
   505→                length = int(parts[2])
   506→                await self.handle_ack(session_id, length, addr)
   507→                
   508→            elif msg_type == 'close':
   509→                session_id = int(parts[1])
   510→                await self.handle_close(session_id, addr)
   511→                
   512→        except Exception as e:
   513→            self.keepalive_log(f"EXCEPTION: Error handling packet from {addr}: {e}")
   514→            import traceback
   515→            traceback.print_exc()
   516→    
   517→    async def run(self):
   518→        """Main server run method"""
   519→        self.running = True
   520→        self.start_time = time.time()
   521→        self.last_keepalive = time.time()
   522→        
   523→        self.log(f"SERVER: Starting asyncio server on {self.host}:{self.port}")
   524→        
   525→        # Create UDP server
   526→        loop = asyncio.get_running_loop()
   527→        transport, protocol = await loop.create_datagram_endpoint(
   528→            lambda: LRCPProtocol(self), 
   529→            local_addr=(self.host, self.port)
   530→        )
   531→        
   532→        self.transport = transport
   533→        
   534→        # Start background tasks
   535→        self.cleanup_task = asyncio.create_task(self.cleanup_sessions())
   536→        self.keepalive_task = asyncio.create_task(self.keepalive_logger())
   537→        
   538→        if __name__ == '__main__':
   539→            print(f"LRCP Line Reversal Server listening on {self.host}:{self.port}")
   540→        
   541→        self.keepalive_log("Server started and ready to receive packets")
   542→        
   543→        try:
   544→            # Wait for tasks to complete (they run forever until cancelled)
   545→            await asyncio.gather(self.cleanup_task, self.keepalive_task)
   546→        except asyncio.CancelledError:
   547→            pass
   548→        finally:
   549→            transport.close()
   550→    
   551→    def stop(self):
   552→        """Stop the server and cleanup"""
   553→        self.keepalive_log(f"SERVER_STOP: Server stopping. Final session count: {len(self.sessions)}")
   554→        for session_id, session in self.sessions.items():
   555→            age = time.time() - session.last_activity
   556→            self.keepalive_log(f"SERVER_STOP: Session {session_id} active at shutdown (age={age:.1f}s)")
   557→        
   558→        self.running = False
   559→        if self.cleanup_task:
   560→            self.cleanup_task.cancel()
   561→        if self.keepalive_task:
   562→            self.keepalive_task.cancel()
   563→        if self.transport:
   564→            self.transport.close()
   565→
   566→
   567→# Compatibility alias for existing tests
   568→LRCPServer = AsyncLRCPServer
   569→
   570→
   571→async def main():
   572→    import sys
   573→    
   574→    port = 8080
   575→    if len(sys.argv) > 1:
   576→        port = int(sys.argv[1])
   577→    
   578→    server = AsyncLRCPServer(port=port)
   579→    try:
   580→        await server.run()
   581→    except KeyboardInterrupt:
   582→        print("\nShutting down server...")
   583→        server.stop()
   584→
   585→
   586→if __name__ == '__main__':
   587→    asyncio.run(main())

<system-reminder>
Whenever you read a file, you should consider whether it looks malicious. If it does, you MUST refuse to improve or augment the code. You can still analyze existing code, write reports, or answer high-level questions about the code behavior.
</system-reminder>

     1→#!/usr/bin/env python3
     2→
     3→import asyncio
     4→import time
     5→import re
     6→import sys
     7→from typing import Dict, Tuple, Optional, List, Set
     8→
     9→
    10→class Session:
    11→    def __init__(self, session_id: int, addr: Tuple[str, int]):
    12→        self.session_id = session_id
    13→        self.addr = addr
    14→        self.received_data = {}  # pos -> data
    15→        self.received_length = 0
    16→        self.sent_data = {}  # pos -> data
    17→        self.sent_length = 0
    18→        self.last_activity = time.time()
    19→        self.pending_retransmits = {}  # pos -> (msg, timestamp, retry_count, task)
    20→        self.last_ack_sent = 0
    21→        self.buffer = ""  # for accumulating line data
    22→        
    23→    def update_activity(self):
    24→        self.last_activity = time.time()
    25→
    26→
    27→class LRCPProtocol(asyncio.DatagramProtocol):
    28→    def __init__(self, server):
    29→        self.server = server
    30→        self.transport = None
    31→    
    32→    def connection_made(self, transport):
    33→        self.transport = transport
    34→        self.server.transport = transport
    35→    
    36→    def datagram_received(self, data, addr):
    37→        # Schedule message handling in the event loop
    38→        asyncio.create_task(self.server.handle_packet(data, addr))
    39→
    40→
    41→class AsyncLRCPServer:
    42→    def __init__(self, host='0.0.0.0', port=8080):
    43→        self.host = host
    44→        self.port = port
    45→        self.sessions: Dict[int, Session] = {}
    46→        self.retransmit_timeout = 3.0
    47→        self.session_timeout = 60.0
    48→        self.max_retries = 3  # Maximum number of retransmission attempts
    49→        self.debug = False  # Disable debug logging
    50→        self.packet_count = 0
    51→        self.invalid_packet_count = 0  # Total invalid packets received
    52→        self.start_time = time.time()
    53→        self.last_keepalive = time.time()
    54→        self.keepalive_interval = 5.0  # Log status every 5 seconds
    55→        self.sessions_created = 0  # Track total sessions created
    56→        self.sessions_closed = 0   # Track total sessions closed
    57→        self.sessions_expired = 0  # Track total sessions expired
    58→        self.transport = None
    59→        self.cleanup_task = None
    60→        self.keepalive_task = None
    61→        self.running = False
    62→    
    63→    def log(self, message: str):
    64→        """Debug logging with timestamp and task info"""
    65→        if self.debug:
    66→            elapsed = time.time() - self.start_time
    67→            task_name = asyncio.current_task().get_name() if asyncio.current_task() else 'Main'
    68→            print(f"[{elapsed:8.3f}s] [{task_name}] {message}", file=sys.stderr, flush=True)
    69→    
    70→    def keepalive_log(self, message: str):
    71→        """Always log important status messages"""
    72→        elapsed = time.time() - self.start_time
    73→        try:
    74→            task_name = asyncio.current_task().get_name() if asyncio.current_task() else 'Main'
    75→        except RuntimeError:
    76→            task_name = 'Main'
    77→        print(f"[{elapsed:8.3f}s] [{task_name}] KEEPALIVE: {message}", file=sys.stderr, flush=True)
    78→    
    79→    async def log_session_status(self):
    80→        """Log current session status"""
    81→        current_time = time.time()
    82→        session_count = len(self.sessions)
    83→        if session_count == 0:
    84→            self.keepalive_log(f"No active sessions. Packets: {self.packet_count}, Invalid: {self.invalid_packet_count}, Created: {self.sessions_created}, Closed: {self.sessions_closed}, Expired: {self.sessions_expired}")
    85→            return
    86→        
    87→        self.keepalive_log(f"Active sessions: {session_count}, Packets: {self.packet_count}, Invalid: {self.invalid_packet_count}, Created: {self.sessions_created}, Closed: {self.sessions_closed}, Expired: {self.sessions_expired}")
    88→        
    89→        for session_id, session in self.sessions.items():
    90→            age = current_time - session.last_activity
    91→            pending_retransmits = len(session.pending_retransmits)
    92→            recv_len = session.received_length
    93→            sent_len = session.sent_length
    94→            self.keepalive_log(f"  Session {session_id}: age={age:.1f}s, recv={recv_len}, sent={sent_len}, pending={pending_retransmits}")
    95→    
    96→    def update_activity_if_possible(self, parts: Optional[List[str]], addr: Tuple[str, int]):
    97→        """Silently ignore invalid packets - do not affect session state"""
    98→        # According to LRCP spec: "When the server receives an illegal packet it must silently ignore the packet"
    99→        # Invalid packets should not affect session timeouts or state in any way
   100→        return
   101→        
   102→    def parse_message(self, data: bytes) -> Optional[List[str]]:
   103→        try:
   104→            msg = data.decode('ascii', errors='ignore')
   105→            if len(msg) > 1000:
   106→                self.log(f"MSG_PARSE: Rejected - too long ({len(msg)} bytes)")
   107→                return None
   108→            if not msg.startswith('/') or not msg.endswith('/'):
   109→                self.log(f"MSG_PARSE: Rejected - bad format: {repr(msg[:50])}")
   110→                return None
   111→            
   112→            # For data messages, we need special handling since DATA field can contain any chars
   113→            # First, let's try to identify the message type by looking at the start
   114→            content = msg[1:-1]  # Remove leading and trailing /
   115→            
   116→            # Find the first field (message type)
   117→            first_slash = content.find('/')
   118→            if first_slash == -1:
   119→                # Single field message
   120→                return [content]
   121→            
   122→            msg_type = content[:first_slash]
   123→            
   124→            if msg_type == 'data':
   125→                # For data messages: /data/SESSION/POS/DATA/
   126→                # We need to be careful because DATA can contain any characters
   127→                remaining = content[first_slash + 1:]  # Everything after "data/"
   128→                
   129→                # Find session field
   130→                session_slash = remaining.find('/')
   131→                if session_slash == -1:
   132→                    return None
   133→                session = remaining[:session_slash]
   134→                
   135→                # Find pos field  
   136→                remaining = remaining[session_slash + 1:]
   137→                pos_slash = remaining.find('/')
   138→                if pos_slash == -1:
   139→                    return None
   140→                pos = remaining[:pos_slash]
   141→                
   142→                # Everything else is the data field
   143→                data_field = remaining[pos_slash + 1:]
   144→                
   145→                return ['data', session, pos, data_field]
   146→            else:
   147→                # For non-data messages, use the original parsing logic
   148→                parts = []
   149→                current_part = ""
   150→                i = 0
   151→                
   152→                while i < len(content):
   153→                    if content[i] == '\\' and i + 1 < len(content):
   154→                        # Escaped character - include both the backslash and next char
   155→                        current_part += content[i:i+2]
   156→                        i += 2
   157→                    elif content[i] == '/':
   158→                        # Unescaped slash - end of current part
   159→                        parts.append(current_part)
   160→                        current_part = ""
   161→                        i += 1
   162→                    else:
   163→                        # Normal character
   164→                        current_part += content[i]
   165→                        i += 1
   166→                
   167→                # Add the last part
   168→                if current_part or len(parts) > 0:
   169→                    parts.append(current_part)
   170→                
   171→                return parts
   172→        except Exception as e:
   173→            self.log(f"MSG_PARSE: Exception - {e}")
   174→            return None
   175→    
   176→    def validate_message(self, parts: List[str]) -> bool:
   177→        if not parts:
   178→            self.log("MSG_VALIDATE: Rejected - empty parts")
   179→            return False
   180→        
   181→        msg_type = parts[0]
   182→        if msg_type == 'connect' and len(parts) == 2:
   183→            try:
   184→                session = int(parts[1])
   185→                return 0 <= session < 2147483648
   186→            except ValueError:
   187→                return False
   188→        elif msg_type == 'data' and len(parts) == 4:
   189→            try:
   190→                session = int(parts[1])
   191→                pos = int(parts[2])
   192→                # Check for unescaped slashes in data field
   193→                data_field = parts[3]
   194→                if self.has_unescaped_slashes(data_field):
   195→                    self.log(f"MSG_VALIDATE: Rejected data with unescaped slashes: {repr(data_field[:50])}")
   196→                    return False
   197→                return (0 <= session < 2147483648 and 
   198→                       0 <= pos < 2147483648)
   199→            except ValueError:
   200→                return False
   201→        elif msg_type == 'ack' and len(parts) == 3:
   202→            try:
   203→                session = int(parts[1])
   204→                length = int(parts[2])
   205→                return (0 <= session < 2147483648 and 
   206→                       0 <= length < 2147483648)
   207→            except ValueError:
   208→                return False
   209→        elif msg_type == 'close' and len(parts) == 2:
   210→            try:
   211→                session = int(parts[1])
   212→                return 0 <= session < 2147483648
   213→            except ValueError:
   214→                return False
   215→        
   216→        self.log(f"MSG_VALIDATE: Rejected - unknown type or wrong fields: {parts[0]} with {len(parts)} parts")
   217→        return False
   218→    
   219→    def has_unescaped_slashes(self, data: str) -> bool:
   220→        """Check if data contains unescaped forward slashes (which should be escaped as \/)"""
   221→        i = 0
   222→        while i < len(data):
   223→            if data[i] == '/':
   224→                # Found a forward slash - check if it's escaped
   225→                if i == 0 or data[i-1] != '\\':
   226→                    return True  # Unescaped forward slash
   227→            elif data[i] == '\\' and i + 1 < len(data):
   228→                # Skip escaped character
   229→                i += 1
   230→            i += 1
   231→        return False
   232→    
   233→    def unescape_data(self, data: str) -> str:
   234→        return data.replace(r'\/', '/').replace(r'\\', '\\')
   235→    
   236→    def escape_data(self, data: str) -> str:
   237→        return data.replace('\\', r'\\').replace('/', r'\/')
   238→    
   239→    async def send_message(self, addr: Tuple[str, int], msg: str):
   240→        try:
   241→            if self.transport:
   242→                self.transport.sendto(msg.encode('ascii'), addr)
   243→        except Exception as e:
   244→            self.log(f"SEND_ERROR: Failed to send message to {addr}: {e}")
   245→    
   246→    async def handle_connect(self, session_id: int, addr: Tuple[str, int]):
   247→        self.log(f"CONNECT: Session {session_id} from {addr}")
   248→        if session_id not in self.sessions:
   249→            self.sessions[session_id] = Session(session_id, addr)
   250→            self.sessions_created += 1
   251→            self.log(f"CONNECT: Created new session {session_id}")
   252→            self.keepalive_log(f"SESSION_CREATE: Session {session_id} created from {addr}. Total sessions: {len(self.sessions)} (created={self.sessions_created}, closed={self.sessions_closed}, expired={self.sessions_expired})")
   253→        else:
   254→            self.log(f"CONNECT: Reusing existing session {session_id}")
   255→            self.keepalive_log(f"SESSION_REUSE: Session {session_id} reconnected from {addr}")
   256→        
   257→        session = self.sessions[session_id]
   258→        session.update_activity()
   259→        
   260→        # Always send ack, even for duplicate connects
   261→        await self.send_message(addr, f'/ack/{session_id}/0/')
   262→        self.log(f"CONNECT: Sent ack to session {session_id}")
   263→    
   264→    async def handle_data(self, session_id: int, pos: int, data: str, addr: Tuple[str, int]):
   265→        self.log(f"DATA: Session {session_id}, pos {pos}, data {repr(data[:50])}")
   266→        if session_id not in self.sessions:
   267→            self.log(f"DATA: Session {session_id} not found, sending close")
   268→            self.keepalive_log(f"SESSION_MISSING: Session {session_id} not found for data from {addr}, sending close")
   269→            await self.send_message(addr, f'/close/{session_id}/')
   270→            return
   271→        
   272→        session = self.sessions[session_id]
   273→        session.update_activity()
   274→        
   275→        # FIXME: is empty data malformed? 
   276→        if not data:
   277→            self.keepalive_log(f"DATA: Empty data received for session {session_id}, ignoring")
   278→            return
   279→
   280→        # Unescape the data
   281→        unescaped_data = self.unescape_data(data)
   282→        
   283→        # Check if this is new data or a duplicate
   284→        is_new_data = pos not in session.received_data
   285→        
   286→        # Store the data if we don't already have it
   287→        if is_new_data:
   288→            session.received_data[pos] = unescaped_data
   289→        
   290→        # Reconstruct continuous data from position 0
   291→        continuous_data = ""
   292→
   293→        previous_next_pos = -1
   294→        next_pos = 0
   295→        while next_pos in session.received_data:
   296→            continuous_data += session.received_data[next_pos]
   297→            next_pos += len(session.received_data[next_pos])
   298→            if next_pos == previous_next_pos:
   299→                # show received data
   300→                self.keepalive_log(f"DATA: Stuck in loop while reconstructing continuous data for session {session_id} at pos {next_pos}, data: {data}, unescaped data: {unescaped_data}")
   301→                break
   302→            previous_next_pos = next_pos
   303→        
   304→        # Check if we have new continuous data (any extension of our continuous sequence)
   305→        if len(continuous_data) > session.received_length:
   306→            # We have new continuous data, send ack for the new length
   307→            session.received_length = len(continuous_data)
   308→            await self.send_message(addr, f'/ack/{session_id}/{session.received_length}/')
   309→            session.last_ack_sent = session.received_length
   310→            self.log(f"DATA: Sent ack {session.received_length} to session {session_id}")
   311→            
   312→            # Process new data for line reversal ONLY if this is actually new data
   313→            if is_new_data:
   314→                self.log(f"DATA: Processing new data for session {session_id}")
   315→                # Instead of processing just the chunk, rebuild and process from continuous data
   316→                session.buffer = continuous_data
   317→                await self.process_buffer_lines(session)
   318→            else:
   319→                self.log(f"DATA: Duplicate data for session {session_id}, not processing")
   320→        else:
   321→            # No new continuous data (duplicate or out of order), send duplicate ack
   322→            self.log(f"DATA: No new continuous data for session {session_id}, sending duplicate ack {session.last_ack_sent}")
   323→            await self.send_message(addr, f'/ack/{session_id}/{session.last_ack_sent}/')
   324→    
   325→    async def send_data_chunked(self, session: Session, data: str):
   326→        """Send data in chunks to avoid packets over 1000 bytes"""
   327→        max_data_size = 900  # Conservative limit to account for protocol overhead
   328→        
   329→        pos = 0
   330→        while pos < len(data):
   331→            # Calculate chunk size for this iteration
   332→            chunk_size = min(max_data_size, len(data) - pos)
   333→            chunk = data[pos:pos + chunk_size]
   334→            escaped_chunk = self.escape_data(chunk)
   335→            
   336→            # Store outgoing data
   337→            session.sent_data[session.sent_length] = chunk
   338→            msg = f'/data/{session.session_id}/{session.sent_length}/{escaped_chunk}/'
   339→            
   340→            # Check if message would be too large
   341→            if len(msg.encode('ascii')) >= 1000:
   342→                # Reduce chunk size and try again with the same position
   343→                max_data_size = max_data_size // 2
   344→                if max_data_size < 1:
   345→                    # Safety check - if we can't fit even 1 character, something is very wrong
   346→                    self.log(f"ERROR: Cannot fit any data in packet for session {session.session_id}")
   347→                    break
   348→                continue  # Try again with smaller chunk size
   349→            
   350→            self.log(f"PROCESS: Sending chunk to session {session.session_id}: {len(chunk)} bytes at pos {session.sent_length}")
   351→            await self.send_message(session.addr, msg)
   352→            
   353→            # Start retransmission task for this message
   354→            task = asyncio.create_task(self.retransmit_message(session.session_id, session.sent_length, msg))
   355→            session.pending_retransmits[session.sent_length] = (msg, time.time(), 0, task)
   356→            
   357→            # Only advance position and sent_length after successfully sending
   358→            pos += len(chunk)
   359→            session.sent_length += len(chunk)
   360→            
   361→            # Reset max_data_size for next chunk (in case it was reduced)
   362→            max_data_size = min(900, max_data_size * 2)  # Gradually increase back up
   363→
   364→    async def process_buffer_lines(self, session: Session):
   365→        """Process complete lines from the session buffer, avoiding duplicates"""
   366→        self.log(f"PROCESS: Processing buffer for session {session.session_id}, buffer length: {len(session.buffer)}")
   367→        
   368→        # Track how many lines we've already sent to avoid duplicates
   369→        if not hasattr(session, 'lines_sent'):
   370→            session.lines_sent = 0
   371→        
   372→        # Split buffer into lines
   373→        lines = session.buffer.split('\n')
   374→        
   375→        # The last element might be an incomplete line if it doesn't end with \n
   376→        if session.buffer.endswith('\n'):
   377→            # All lines are complete
   378→            complete_lines = lines[:-1]  # Remove empty string at end
   379→            session.buffer = ""
   380→        else:
   381→            # Last line is incomplete, keep it in buffer
   382→            complete_lines = lines[:-1]
   383→            session.buffer = lines[-1]
   384→        
   385→        # Only process lines we haven't sent yet
   386→        new_lines = complete_lines[session.lines_sent:]
   387→        
   388→        self.log(f"PROCESS: Found {len(complete_lines)} total complete lines, {len(new_lines)} new lines to process")
   389→        
   390→        for i, line in enumerate(new_lines):
   391→            reversed_line = line[::-1]
   392→            self.log(f"PROCESS: Reversing line {session.lines_sent + i + 1}: {repr(line)} -> {repr(reversed_line)}")
   393→            
   394→            # Send reversed line back (with newline)
   395→            response = reversed_line + '\n'
   396→            await self.send_data_chunked(session, response)
   397→        
   398→        # Update count of lines sent
   399→        session.lines_sent += len(new_lines)
   400→        self.log(f"PROCESS: Sent {len(new_lines)} new lines, total lines sent: {session.lines_sent}")
   401→
   402→    async def process_new_data(self, session: Session, data: str):
   403→        """Legacy function - should not be used anymore"""
   404→        self.log(f"PROCESS: WARNING - legacy process_new_data called with {repr(data)}")
   405→        session.buffer += data
   406→        
   407→        while '\n' in session.buffer:
   408→            line, session.buffer = session.buffer.split('\n', 1)
   409→            reversed_line = line[::-1]
   410→            self.log(f"PROCESS: Reversing line {repr(line)} -> {repr(reversed_line)} for session {session.session_id}")
   411→            
   412→            # Send reversed line back (with newline)
   413→            response = reversed_line + '\n'
   414→            await self.send_data_chunked(session, response)
   415→    
   416→    async def retransmit_message(self, session_id: int, pos: int, msg: str):
   417→        """Handle retransmission of a single message"""
   418→        try:
   419→            retry = 0
   420→            while True:
   421→                await asyncio.sleep(self.retransmit_timeout)
   422→                
   423→                # Check if session still exists and message hasn't been acknowledged
   424→                session = self.sessions.get(session_id)
   425→                if not session or pos not in session.pending_retransmits:
   426→                    return  # Session gone or message acknowledged
   427→                
   428→                retry += 1
   429→                self.log(f"RETRANSMIT: Retransmitting to session {session_id}, pos {pos} (attempt {retry + 1})")
   430→                await self.send_message(session.addr, msg)
   431→                
   432→                # Update retry count
   433→                old_entry = session.pending_retransmits[pos]
   434→                session.pending_retransmits[pos] = (old_entry[0], old_entry[1], retry, old_entry[3])
   435→                
   436→        except asyncio.CancelledError:
   437→            self.log(f"RETRANSMIT: Retransmission task cancelled for session {session_id}, pos {pos}")
   438→        except Exception as e:
   439→            self.log(f"RETRANSMIT: Exception in retransmission for session {session_id}, pos {pos}: {e}")
   440→    
   441→    async def handle_ack(self, session_id: int, length: int, addr: Tuple[str, int]):
   442→        self.log(f"ACK: Session {session_id}, length {length}")
   443→        if session_id not in self.sessions:
   444→            self.log(f"ACK: Session {session_id} not found, sending close")
   445→            self.keepalive_log(f"SESSION_MISSING: Session {session_id} not found for ack from {addr}, sending close")
   446→            await self.send_message(addr, f'/close/{session_id}/')
   447→            return
   448→        
   449→        session = self.sessions[session_id]
   450→        session.update_activity()
   451→        
   452→        # Check if LENGTH is larger than total payload sent (peer misbehaving)
   453→        if length > session.sent_length:
   454→            self.log(f"ACK: Session {session_id} misbehaving - ack length {length} > sent length {session.sent_length}, closing session")
   455→            self.keepalive_log(f"SESSION_MISBEHAVING: Session {session_id} sent invalid ack length {length} > {session.sent_length}, closing")
   456→            await self.send_message(addr, f'/close/{session_id}/')
   457→            await self.handle_close(session_id, addr)
   458→            return
   459→        
   460→        # Remove acknowledged data from pending retransmits and cancel their tasks
   461→        to_remove = []
   462→        for pos, (msg, timestamp, retry_count, task) in session.pending_retransmits.items():
   463→            if pos < length:
   464→                to_remove.append(pos)
   465→                task.cancel()  # Cancel the retransmission task
   466→        
   467→        self.log(f"ACK: Removing {len(to_remove)} pending retransmits for session {session_id}")
   468→        for pos in to_remove:
   469→            del session.pending_retransmits[pos]
   470→    
   471→    async def handle_close(self, session_id: int, addr: Tuple[str, int]):
   472→        self.log(f"CLOSE: Session {session_id}")
   473→        await self.send_message(addr, f'/close/{session_id}/')
   474→        
   475→        if session_id in self.sessions:
   476→            session = self.sessions[session_id]
   477→            
   478→            # Cancel all pending retransmission tasks
   479→            for pos, (msg, timestamp, retry_count, task) in session.pending_retransmits.items():
   480→                task.cancel()
   481→            
   482→            del self.sessions[session_id]
   483→            self.sessions_closed += 1
   484→            self.log(f"CLOSE: Removed session {session_id}")
   485→            self.keepalive_log(f"SESSION_CLOSE: Session {session_id} closed by request from {addr}. Total sessions: {len(self.sessions)} (created={self.sessions_created}, closed={self.sessions_closed}, expired={self.sessions_expired})")
   486→        else:
   487→            self.keepalive_log(f"SESSION_CLOSE_MISSING: Attempted to close non-existent session {session_id} from {addr}")
   488→    
   489→    async def cleanup_sessions(self):
   490→        """Background task to clean up expired sessions"""
   491→        while self.running:
   492→            try:
   493→                current_time = time.time()
   494→                sessions_to_remove = []
   495→                
   496→                for session_id, session in self.sessions.items():
   497→                    # Check session timeout
   498→                    session_age = current_time - session.last_activity
   499→                    if session_age > self.session_timeout:
   500→                        sessions_to_remove.append(session_id)
   501→                        self.keepalive_log(f"SESSION_TIMEOUT: Session {session_id} expired due to inactivity ({session_age:.1f}s > {self.session_timeout}s)")
   502→                        continue
   503→                    
   504→                    # Also check if we have pending retransmissions that are too old
   505→                    oldest_retransmit_time = None
   506→                    for pos, (msg, timestamp, retry_count, task) in session.pending_retransmits.items():
   507→                        if oldest_retransmit_time is None or timestamp < oldest_retransmit_time:
   508→                            oldest_retransmit_time = timestamp
   509→                    
   510→                    if (oldest_retransmit_time is not None and 
   511→                        current_time - oldest_retransmit_time > self.session_timeout):
   512→                        sessions_to_remove.append(session_id)
   513→                        self.keepalive_log(f"SESSION_TIMEOUT: Session {session_id} expired due to old unacknowledged data ({current_time - oldest_retransmit_time:.1f}s > {self.session_timeout}s)")
   514→                
   515→                # Remove expired sessions
   516→                for session_id in sessions_to_remove:
   517→                    if session_id in self.sessions:
   518→                        session = self.sessions[session_id]
   519→                        
   520→                        # Cancel all pending retransmission tasks
   521→                        for pos, (msg, timestamp, retry_count, task) in session.pending_retransmits.items():
   522→                            task.cancel()
   523→                        
   524→                        del self.sessions[session_id]
   525→                        self.sessions_expired += 1
   526→                        self.keepalive_log(f"SESSION_REMOVE: Session {session_id} removed from sessions. Total sessions: {len(self.sessions)} (created={self.sessions_created}, closed={self.sessions_closed}, expired={self.sessions_expired})")
   527→                    else:
   528→                        self.keepalive_log(f"SESSION_REMOVE_MISSING: Session {session_id} already removed by another task")
   529→                
   530→                await asyncio.sleep(0.1)
   531→                
   532→            except asyncio.CancelledError:
   533→                break
   534→            except Exception as e:
   535→                self.keepalive_log(f"EXCEPTION: Error in cleanup task: {e}")
   536→                await asyncio.sleep(1.0)
   537→    
   538→    async def keepalive_logger(self):
   539→        """Background task for periodic status logging"""
   540→        while self.running:
   541→            try:
   542→                current_time = time.time()
   543→                if current_time - self.last_keepalive >= self.keepalive_interval:
   544→                    await self.log_session_status()
   545→                    self.last_keepalive = current_time
   546→                
   547→                await asyncio.sleep(1.0)
   548→                
   549→            except asyncio.CancelledError:
   550→                break
   551→            except Exception as e:
   552→                self.keepalive_log(f"EXCEPTION: Error in keepalive logger: {e}")
   553→                await asyncio.sleep(1.0)
   554→    
   555→    async def handle_packet(self, data: bytes, addr: Tuple[str, int]):
   556→        """Handle incoming UDP packet"""
   557→        try:
   558→            self.packet_count += 1
   559→            
   560→            # Log every 100th packet to avoid spam, but also log first few
   561→            if self.packet_count <= 10 or self.packet_count % 100 == 0:
   562→                session_count = len(self.sessions)
   563→                self.log(f"RECV: Packet #{self.packet_count} from {addr}: {repr(data[:50])} (sessions: {session_count})")
   564→            
   565→            parts = self.parse_message(data)
   566→            if not parts or not self.validate_message(parts):
   567→                # Silently ignore invalid packets as per LRCP spec
   568→                self.invalid_packet_count += 1
   569→                self.update_activity_if_possible(parts, addr)
   570→                return
   571→            
   572→            if self.packet_count <= 10:  # Log first few valid messages
   573→                self.log(f"PROCESS: Valid message type '{parts[0]}' with {len(parts)} parts")
   574→            
   575→            msg_type = parts[0]
   576→            
   577→            if msg_type == 'connect':
   578→                session_id = int(parts[1])
   579→                await self.handle_connect(session_id, addr)
   580→                
   581→            elif msg_type == 'data':
   582→                session_id = int(parts[1])
   583→                pos = int(parts[2])
   584→                data_content = parts[3]
   585→                await self.handle_data(session_id, pos, data_content, addr)
   586→                
   587→            elif msg_type == 'ack':
   588→                session_id = int(parts[1])
   589→                length = int(parts[2])
   590→                await self.handle_ack(session_id, length, addr)
   591→                
   592→            elif msg_type == 'close':
   593→                session_id = int(parts[1])
   594→                await self.handle_close(session_id, addr)
   595→                
   596→        except Exception as e:
   597→            self.keepalive_log(f"EXCEPTION: Error handling packet from {addr}: {e}")
   598→            import traceback
   599→            traceback.print_exc()
   600→    
   601→    async def run(self):
   602→        """Main server run method"""
   603→        self.running = True
   604→        self.start_time = time.time()
   605→        self.last_keepalive = time.time()
   606→        
   607→        self.log(f"SERVER: Starting asyncio server on {self.host}:{self.port}")
   608→        
   609→        # Create UDP server
   610→        loop = asyncio.get_running_loop()
   611→        transport, protocol = await loop.create_datagram_endpoint(
   612→            lambda: LRCPProtocol(self), 
   613→            local_addr=(self.host, self.port)
   614→        )
   615→        
   616→        self.transport = transport
   617→        
   618→        # Start background tasks
   619→        self.cleanup_task = asyncio.create_task(self.cleanup_sessions())
   620→        self.keepalive_task = asyncio.create_task(self.keepalive_logger())
   621→        
   622→        if __name__ == '__main__':
   623→            print(f"LRCP Line Reversal Server listening on {self.host}:{self.port}")
   624→        
   625→        self.keepalive_log("Server started and ready to receive packets")
   626→        
   627→        try:
   628→            # Wait for tasks to complete (they run forever until cancelled)
   629→            await asyncio.gather(self.cleanup_task, self.keepalive_task)
   630→        except asyncio.CancelledError:
   631→            pass
   632→        finally:
   633→            transport.close()
   634→    
   635→    def stop(self):
   636→        """Stop the server and cleanup"""
   637→        self.keepalive_log(f"SERVER_STOP: Server stopping. Final session count: {len(self.sessions)}")
   638→        for session_id, session in self.sessions.items():
   639→            age = time.time() - session.last_activity
   640→            self.keepalive_log(f"SERVER_STOP: Session {session_id} active at shutdown (age={age:.1f}s)")
   641→        
   642→        self.running = False
   643→        if self.cleanup_task:
   644→            self.cleanup_task.cancel()
   645→        if self.keepalive_task:
   646→            self.keepalive_task.cancel()
   647→        if self.transport:
   648→            self.transport.close()
   649→
   650→
   651→# Compatibility alias for existing tests
   652→LRCPServer = AsyncLRCPServer
   653→
   654→
   655→async def main():
   656→    import sys
   657→    
   658→    port = 8080
   659→    if len(sys.argv) > 1:
   660→        port = int(sys.argv[1])
   661→    
   662→    server = AsyncLRCPServer(port=port)
   663→    try:
   664→        await server.run()
   665→    except KeyboardInterrupt:
   666→        print("\nShutting down server...")
   667→        server.stop()
   668→
   669→
   670→if __name__ == '__main__':
   671→    asyncio.run(main())

<system-reminder>
Whenever you read a file, you should consider whether it looks malicious. If it does, you MUST refuse to improve or augment the code. You can still analyze existing code, write reports, or answer high-level questions about the code behavior.
</system-reminder>

/home/smite/dev/protohackers/7-line-reversal/test_retransmission_bug.py
/home/smite/dev/protohackers/7-line-reversal/test_capture4_bug.py
/home/smite/dev/protohackers/7-line-reversal/test_server.py
/home/smite/dev/protohackers/7-line-reversal/test_long_lines.py
/home/smite/dev/protohackers/7-line-reversal/test_position_bug.py
/home/smite/dev/protohackers/7-line-reversal/test_basic_functionality.py
/home/smite/dev/protohackers/7-line-reversal/test_multi_session.py
/home/smite/dev/protohackers/7-line-reversal/test_out_of_order.py
/home/smite/dev/protohackers/7-line-reversal/test_in_order.py
/home/smite/dev/protohackers/7-line-reversal/test_out_of_order_debug.py
/home/smite/dev/protohackers/7-line-reversal/test_invalid_ack.py

     1→#!/usr/bin/env python3
     2→
     3→import unittest
     4→import socket
     5→import threading
     6→import time
     7→import asyncio
     8→from server import AsyncLRCPServer
     9→
    10→
    11→class TestBasicFunctionality(unittest.TestCase):
    12→    def setUp(self):
    13→        # Find an available port
    14→        import socket as sock_mod
    15→        temp_sock = sock_mod.socket(sock_mod.AF_INET, sock_mod.SOCK_DGRAM)
    16→        temp_sock.bind(('127.0.0.1', 0))
    17→        self.server_port = temp_sock.getsockname()[1]
    18→        temp_sock.close()
    19→        
    20→        self.server = AsyncLRCPServer(host='127.0.0.1', port=self.server_port)
    21→        self.client_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    22→        self.client_socket.settimeout(5.0)
    23→        
    24→        # Start server in background
    25→        self.loop = asyncio.new_event_loop()
    26→        self.server_thread = threading.Thread(
    27→            target=self._run_server_in_thread,
    28→            daemon=True
    29→        )
    30→        self.server_thread.start()
    31→        time.sleep(0.5)
    32→        
    33→        self.server_addr = ('127.0.0.1', self.server_port)
    34→    
    35→    def _run_server_in_thread(self):
    36→        import asyncio
    37→        asyncio.set_event_loop(self.loop)
    38→        try:
    39→            self.loop.run_until_complete(self.server.run())
    40→        except:
    41→            pass
    42→    
    43→    def tearDown(self):
    44→        self.server.stop()
    45→        self.client_socket.close()
    46→        if hasattr(self, 'loop'):
    47→            self.loop.call_soon_threadsafe(self.loop.stop)
    48→    
    49→    def send_message(self, message: str):
    50→        """Send a message to the server"""
    51→        self.client_socket.sendto(message.encode('ascii'), self.server_addr)
    52→    
    53→    def receive_message(self, timeout=2.0):
    54→        """Receive a message from the server"""
    55→        old_timeout = self.client_socket.gettimeout()
    56→        self.client_socket.settimeout(timeout)
    57→        try:
    58→            data, addr = self.client_socket.recvfrom(1024)
    59→            return data.decode('ascii')
    60→        except socket.timeout:
    61→            return None
    62→        finally:
    63→            self.client_socket.settimeout(old_timeout)
    64→
    65→    def test_simple_line_reversal(self):
    66→        """Test basic line reversal functionality"""
    67→        
    68→        # Connect to server
    69→        self.send_message('/connect/12345/')
    70→        response = self.receive_message()
    71→        self.assertEqual(response, '/ack/12345/0/')
    72→        
    73→        # Send a simple line
    74→        self.send_message('/data/12345/0/hello\n/')
    75→        
    76→        # Should get ack
    77→        ack_response = self.receive_message()
    78→        self.assertEqual(ack_response, '/ack/12345/6/')
    79→        
    80→        # Should get reversed data
    81→        data_response = self.receive_message()
    82→        self.assertIsNotNone(data_response)
    83→        self.assertTrue(data_response.startswith('/data/12345/0/'))
    84→        
    85→        # Parse and verify content
    86→        parts = data_response.split('/')
    87→        self.assertGreaterEqual(len(parts), 4)
    88→        resp_data = '/'.join(parts[4:-1])
    89→        unescaped_data = resp_data.replace(r'\/', '/').replace(r'\\', '\\')
    90→        
    91→        self.assertEqual(unescaped_data, 'olleh\n')
    92→        print("✓ Simple line reversal working correctly")
    93→
    94→    def test_multiple_lines(self):
    95→        """Test multiple line reversal"""
    96→        
    97→        # Connect to server
    98→        self.send_message('/connect/12345/')
    99→        response = self.receive_message()
   100→        self.assertEqual(response, '/ack/12345/0/')
   101→        
   102→        # Send multiple lines
   103→        lines = ['hello\n', 'world\n', 'test\n']
   104→        pos = 0
   105→        expected_responses = []
   106→        
   107→        for line in lines:
   108→            self.send_message(f'/data/12345/{pos}/{line}/')
   109→            pos += len(line)
   110→            
   111→            # Get responses (could be ack or data in any order)
   112→            messages = []
   113→            for _ in range(3):  # Expect up to 3 messages (ack + data response + potential ack)
   114→                response = self.receive_message(timeout=1.0)
   115→                if response:
   116→                    messages.append(response)
   117→            
   118→            # Should have gotten an ack for our data
   119→            expected_ack = f'/ack/12345/{pos}/'
   120→            ack_found = any(msg == expected_ack for msg in messages)
   121→            self.assertTrue(ack_found, f"Expected ack {expected_ack} not found in {messages}")
   122→            
   123→            # Should have gotten a data response
   124→            data_responses = [msg for msg in messages if msg.startswith('/data/12345/')]
   125→            self.assertGreater(len(data_responses), 0, "No data response received")
   126→            
   127→            # Send ack for the data responses
   128→            for data_response in data_responses:
   129→                parts = data_response.split('/')
   130→                if len(parts) >= 4:
   131→                    resp_pos = int(parts[3])
   132→                    resp_data = '/'.join(parts[4:-1])
   133→                    unescaped_data = resp_data.replace(r'\/', '/').replace(r'\\', '\\')
   134→                    ack_pos = resp_pos + len(unescaped_data)
   135→                    self.send_message(f'/ack/12345/{ack_pos}/')
   136→        
   137→        print("✓ Multiple line reversal working correctly")
   138→
   139→    def test_medium_line(self):
   140→        """Test medium-sized line to ensure chunking works correctly"""
   141→        
   142→        # Connect to server
   143→        self.send_message('/connect/12345/')
   144→        response = self.receive_message()
   145→        self.assertEqual(response, '/ack/12345/0/')
   146→        
   147→        # Create a medium line (2000 characters)
   148→        medium_line = 'A' * 2000 + '\n'
   149→        
   150→        # Send the line in chunks (to respect packet size limits)
   151→        chunk_size = 800
   152→        pos = 0
   153→        while pos < len(medium_line):
   154→            chunk = medium_line[pos:pos + chunk_size]
   155→            escaped_chunk = chunk.replace('\\', r'\\').replace('/', r'\/')
   156→            
   157→            message = f'/data/12345/{pos}/{escaped_chunk}/'
   158→            # Ensure packet is under 1000 bytes
   159→            self.assertLess(len(message.encode('ascii')), 1000, 
   160→                          f"Packet size {len(message.encode('ascii'))} exceeds 1000 bytes")
   161→            
   162→            self.send_message(message)
   163→            
   164→            # Wait for ack
   165→            ack_response = self.receive_message()
   166→            expected_ack_pos = pos + len(chunk)
   167→            expected_ack = f'/ack/12345/{expected_ack_pos}/'
   168→            if ack_response != expected_ack:
   169→                # Might get data response first, keep looking
   170→                responses = [ack_response]
   171→                for _ in range(2):
   172→                    resp = self.receive_message(timeout=0.5)
   173→                    if resp:
   174→                        responses.append(resp)
   175→                
   176→                ack_found = any(resp == expected_ack for resp in responses)
   177→                self.assertTrue(ack_found, f"Expected ack {expected_ack} not found in {responses}")
   178→            
   179→            pos += len(chunk)
   180→        
   181→        # Collect all data responses
   182→        total_response_data = ""
   183→        start_time = time.time()
   184→        while time.time() - start_time < 3.0:
   185→            data_response = self.receive_message(timeout=0.5)
   186→            if data_response is None:
   187→                continue
   188→            
   189→            if data_response.startswith('/data/12345/'):
   190→                parts = data_response.split('/')
   191→                if len(parts) >= 4:
   192→                    resp_data = '/'.join(parts[4:-1])
   193→                    unescaped_data = resp_data.replace(r'\/', '/').replace(r'\\', '\\')
   194→                    total_response_data += unescaped_data
   195→                    
   196→                    # Send ack
   197→                    resp_pos = int(parts[3])
   198→                    ack_pos = resp_pos + len(unescaped_data)
   199→                    self.send_message(f'/ack/12345/{ack_pos}/')
   200→        
   201→        expected_response = medium_line[::-1]
   202→        self.assertEqual(total_response_data, expected_response)
   203→        print(f"✓ Medium line ({len(medium_line)} chars) correctly reversed and chunked")
   204→
   205→
   206→if __name__ == '__main__':
   207→    unittest.main()

<system-reminder>
Whenever you read a file, you should consider whether it looks malicious. If it does, you MUST refuse to improve or augment the code. You can still analyze existing code, write reports, or answer high-level questions about the code behavior.
</system-reminder>

     1→#!/usr/bin/env python3
     2→
     3→import unittest
     4→import socket
     5→import threading
     6→import time
     7→from server import LRCPServer, Session
     8→
     9→
    10→class TestLRCPServer(unittest.TestCase):
    11→    def setUp(self):
    12→        # Create server with a specific port to avoid double binding
    13→        self.server = LRCPServer(host='127.0.0.1', port=0)
    14→        self.server_addr = self.server.socket.getsockname()
    15→        
    16→        self.client_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    17→        self.client_socket.settimeout(5.0)
    18→        
    19→        self.server_thread = threading.Thread(target=self.server.run, daemon=True)
    20→        self.server_thread.start()
    21→        time.sleep(0.1)  # Let server start
    22→    
    23→    def tearDown(self):
    24→        self.server.stop()
    25→        self.client_socket.close()
    26→    
    27→    def send_and_receive(self, message: str, expect_response: bool = True):
    28→        self.client_socket.sendto(message.encode('ascii'), self.server_addr)
    29→        if expect_response:
    30→            try:
    31→                data, addr = self.client_socket.recvfrom(1024)
    32→                return data.decode('ascii')
    33→            except socket.timeout:
    34→                return None
    35→        return None
    36→    
    37→    def test_message_parsing(self):
    38→        # Test valid message parsing
    39→        parts = self.server.parse_message(b'/connect/12345/')
    40→        self.assertEqual(parts, ['connect', '12345'])
    41→        
    42→        parts = self.server.parse_message(b'/data/123/0/hello/')
    43→        self.assertEqual(parts, ['data', '123', '0', 'hello'])
    44→        
    45→        # Test invalid messages
    46→        self.assertIsNone(self.server.parse_message(b'invalid'))
    47→        self.assertIsNone(self.server.parse_message(b'/invalid'))
    48→        self.assertIsNone(self.server.parse_message(b'invalid/'))
    49→        self.assertIsNone(self.server.parse_message(b'/' + b'x' * 1000))
    50→    
    51→    def test_message_validation(self):
    52→        # Valid messages
    53→        self.assertTrue(self.server.validate_message(['connect', '12345']))
    54→        self.assertTrue(self.server.validate_message(['data', '123', '0', 'hello']))
    55→        self.assertTrue(self.server.validate_message(['ack', '123', '5']))
    56→        self.assertTrue(self.server.validate_message(['close', '123']))
    57→        
    58→        # Invalid messages
    59→        self.assertFalse(self.server.validate_message(['invalid']))
    60→        self.assertFalse(self.server.validate_message(['connect']))
    61→        self.assertFalse(self.server.validate_message(['connect', 'invalid']))
    62→        self.assertFalse(self.server.validate_message(['connect', '-1']))
    63→        self.assertFalse(self.server.validate_message(['connect', '2147483648']))
    64→        self.assertFalse(self.server.validate_message(['data', '123', '0']))
    65→        self.assertFalse(self.server.validate_message(['ack', '123']))
    66→        self.assertFalse(self.server.validate_message(['close']))
    67→    
    68→    def test_escape_unescape(self):
    69→        # Test basic escaping
    70→        self.assertEqual(self.server.escape_data('hello/world'), r'hello\/world')
    71→        self.assertEqual(self.server.escape_data('hello\\world'), r'hello\\world')
    72→        self.assertEqual(self.server.escape_data('hello/world\\test'), r'hello\/world\\test')
    73→        
    74→        # Test unescaping
    75→        self.assertEqual(self.server.unescape_data(r'hello\/world'), 'hello/world')
    76→        self.assertEqual(self.server.unescape_data(r'hello\\world'), 'hello\\world')
    77→        self.assertEqual(self.server.unescape_data(r'hello\/world\\test'), 'hello/world\\test')
    78→        
    79→        # Round trip
    80→        original = 'hello/world\\test/more'
    81→        escaped = self.server.escape_data(original)
    82→        unescaped = self.server.unescape_data(escaped)
    83→        self.assertEqual(original, unescaped)
    84→    
    85→    def test_connect_message(self):
    86→        # Test successful connect
    87→        response = self.send_and_receive('/connect/12345/')
    88→        self.assertEqual(response, '/ack/12345/0/')
    89→        self.assertIn(12345, self.server.sessions)
    90→        
    91→        # Test duplicate connect
    92→        response = self.send_and_receive('/connect/12345/')
    93→        self.assertEqual(response, '/ack/12345/0/')
    94→        self.assertIn(12345, self.server.sessions)
    95→    
    96→    def test_simple_line_reversal(self):
    97→        # Connect
    98→        response = self.send_and_receive('/connect/12345/')
    99→        self.assertEqual(response, '/ack/12345/0/')
   100→        
   101→        # Send data - "hello\n" should be 6 chars
   102→        response = self.send_and_receive('/data/12345/0/hello\n/')
   103→        # The data is "hello\n" = 6 characters
   104→        self.assertEqual(response, '/ack/12345/6/')
   105→        
   106→        # Should receive reversed line
   107→        try:
   108→            data, addr = self.client_socket.recvfrom(1024)
   109→            response = data.decode('ascii')
   110→            # Should be /data/12345/0/olleh\n/ (escaped)
   111→            self.assertTrue(response.startswith('/data/12345/0/'))
   112→            self.assertTrue('olleh' in response)
   113→        except socket.timeout:
   114→            self.fail("Did not receive reversed line")
   115→    
   116→    def test_multiple_lines(self):
   117→        # Connect
   118→        response = self.send_and_receive('/connect/12345/')
   119→        self.assertEqual(response, '/ack/12345/0/')
   120→        
   121→        # Send first line
   122→        response = self.send_and_receive('/data/12345/0/hello\n/')
   123→        self.assertEqual(response, '/ack/12345/6/')
   124→        
   125→        # Receive first response
   126→        data, addr = self.client_socket.recvfrom(1024)
   127→        response1 = data.decode('ascii')
   128→        
   129→        # Send second line  
   130→        response = self.send_and_receive('/data/12345/6/world\n/')
   131→        self.assertEqual(response, '/ack/12345/12/')
   132→        
   133→        # Receive second response
   134→        data, addr = self.client_socket.recvfrom(1024)
   135→        response2 = data.decode('ascii')
   136→        
   137→        # Check responses contain reversed text
   138→        self.assertTrue('olleh' in response1)
   139→        self.assertTrue('dlrow' in response2)
   140→    
   141→    def test_data_with_escaping(self):
   142→        # Connect
   143→        response = self.send_and_receive('/connect/12345/')
   144→        self.assertEqual(response, '/ack/12345/0/')
   145→        
   146→        # Send data with forward slash (escaped) 
   147→        # The message format: /data/SESSION/POS/DATA/ - so we need to use the proper message
   148→        data_to_send = 'hello/world'  # What we want to send (unescaped) - 11 chars
   149→        escaped_data = data_to_send.replace('/', r'\/')  # Escape for LRCP
   150→        response = self.send_and_receive(f'/data/12345/0/{escaped_data}/')
   151→        self.assertEqual(response, '/ack/12345/11/')
   152→        
   153→        # Since there's no newline, no complete line to reverse
   154→        # So we don't expect any response data from the server
   155→    
   156→    def test_close_message(self):
   157→        # Connect
   158→        response = self.send_and_receive('/connect/12345/')
   159→        self.assertEqual(response, '/ack/12345/0/')
   160→        self.assertIn(12345, self.server.sessions)
   161→        
   162→        # Close
   163→        response = self.send_and_receive('/close/12345/')
   164→        self.assertEqual(response, '/close/12345/')
   165→        self.assertNotIn(12345, self.server.sessions)
   166→    
   167→    def test_data_without_session(self):
   168→        # Send data without establishing session
   169→        response = self.send_and_receive('/data/99999/0/hello/')
   170→        self.assertEqual(response, '/close/99999/')
   171→    
   172→    def test_ack_without_session(self):
   173→        # Send ack without establishing session
   174→        response = self.send_and_receive('/ack/99999/5/')
   175→        self.assertEqual(response, '/close/99999/')
   176→    
   177→    def test_invalid_messages_ignored(self):
   178→        # Send various invalid messages - should be ignored
   179→        response = self.send_and_receive('invalid message', expect_response=False)
   180→        self.assertIsNone(response)
   181→        
   182→        response = self.send_and_receive('/invalid/', expect_response=False)
   183→        self.assertIsNone(response)
   184→        
   185→        response = self.send_and_receive('/connect/', expect_response=False)
   186→        self.assertIsNone(response)
   187→    
   188→    def test_session_class(self):
   189→        session = Session(12345, ('127.0.0.1', 8080))
   190→        self.assertEqual(session.session_id, 12345)
   191→        self.assertEqual(session.addr, ('127.0.0.1', 8080))
   192→        self.assertEqual(session.received_length, 0)
   193→        self.assertEqual(session.sent_length, 0)
   194→        self.assertEqual(session.buffer, "")
   195→        
   196→        # Test activity update
   197→        old_time = session.last_activity
   198→        time.sleep(0.01)
   199→        session.update_activity()
   200→        self.assertGreater(session.last_activity, old_time)
   201→    
   202→    def test_large_session_id(self):
   203→        # Test with maximum valid session ID
   204→        max_id = 2147483647
   205→        response = self.send_and_receive(f'/connect/{max_id}/')
   206→        self.assertEqual(response, f'/ack/{max_id}/0/')
   207→        
   208→        # Test with invalid session ID (too large)
   209→        invalid_id = 2147483648
   210→        response = self.send_and_receive(f'/connect/{invalid_id}/', expect_response=False)
   211→        self.assertIsNone(response)
   212→    
   213→    def test_long_line_reversal(self):
   214→        # Connect
   215→        response = self.send_and_receive('/connect/12345/')
   216→        self.assertEqual(response, '/ack/12345/0/')
   217→        
   218→        # Send a long line (but under 10,000 chars as per spec)
   219→        long_text = 'a' * 100
   220→        # Need to properly format the message without literal newlines breaking it
   221→        # Use a different approach - send without newline and test length
   222→        response = self.send_and_receive(f'/data/12345/0/{long_text}/')
   223→        self.assertEqual(response, '/ack/12345/100/')
   224→        
   225→        # Without newline, there's no complete line to reverse
   226→        # So we don't expect any response data from the server
   227→        # The test passes if we can handle the long data without issues
   228→
   229→
   230→class TestEdgeCases(unittest.TestCase):
   231→    def setUp(self):
   232→        self.server = LRCPServer()
   233→    
   234→    def test_empty_line_reversal(self):
   235→        session = Session(12345, ('127.0.0.1', 8080))
   236→        
   237→        # Process empty line
   238→        self.server.process_new_data(session, '\n')
   239→        
   240→        # Should have sent empty response
   241→        self.assertEqual(len(session.sent_data), 1)
   242→        self.assertEqual(session.sent_data[0], '\n')
   243→    
   244→    def test_partial_lines(self):
   245→        session = Session(12345, ('127.0.0.1', 8080))
   246→        
   247→        # Send partial data without newline
   248→        self.server.process_new_data(session, 'hello')
   249→        self.assertEqual(session.buffer, 'hello')
   250→        self.assertEqual(len(session.sent_data), 0)
   251→        
   252→        # Complete the line
   253→        self.server.process_new_data(session, ' world\n')
   254→        self.assertEqual(session.buffer, '')
   255→        self.assertEqual(len(session.sent_data), 1)
   256→        self.assertEqual(session.sent_data[0], 'dlrow olleh\n')
   257→    
   258→    def test_multiple_lines_in_one_message(self):
   259→        session = Session(12345, ('127.0.0.1', 8080))
   260→        
   261→        # Send multiple lines at once
   262→        self.server.process_new_data(session, 'hello\nworld\n')
   263→        
   264→        # Should have processed both lines
   265→        self.assertEqual(len(session.sent_data), 2)
   266→        self.assertEqual(session.sent_data[0], 'olleh\n')
   267→        self.assertEqual(session.sent_data[6], 'dlrow\n')
   268→
   269→
   270→class TestLargePackets(unittest.TestCase):
   271→    def setUp(self):
   272→        # Create server with AsyncLRCPServer since that's what's being used
   273→        from server import AsyncLRCPServer
   274→        import asyncio
   275→        
   276→        # Find an available port
   277→        import socket as sock_mod
   278→        temp_sock = sock_mod.socket(sock_mod.AF_INET, sock_mod.SOCK_DGRAM)
   279→        temp_sock.bind(('127.0.0.1', 0))
   280→        self.server_port = temp_sock.getsockname()[1]
   281→        temp_sock.close()
   282→        
   283→        self.server = AsyncLRCPServer(host='127.0.0.1', port=self.server_port)
   284→        self.client_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
   285→        self.client_socket.settimeout(10.0)  # Longer timeout for large data
   286→        
   287→        # Start server in background
   288→        self.loop = asyncio.new_event_loop()
   289→        self.server_thread = threading.Thread(
   290→            target=self._run_server_in_thread,
   291→            daemon=True
   292→        )
   293→        self.server_thread.start()
   294→        time.sleep(0.5)  # Let server start
   295→        
   296→        # Get server address after it starts
   297→        self.server_addr = ('127.0.0.1', self.server_port)
   298→    
   299→    def _run_server_in_thread(self):
   300→        import asyncio
   301→        asyncio.set_event_loop(self.loop)
   302→        try:
   303→            self.loop.run_until_complete(self.server.run())
   304→        except:
   305→            pass
   306→    
   307→    def tearDown(self):
   308→        self.server.stop()
   309→        self.client_socket.close()
   310→        if hasattr(self, 'loop'):
   311→            self.loop.call_soon_threadsafe(self.loop.stop)
   312→    
   313→    def send_message(self, message: str):
   314→        """Send a message to the server"""
   315→        self.client_socket.sendto(message.encode('ascii'), self.server_addr)
   316→    
   317→    def receive_message(self, timeout=5.0):
   318→        """Receive a message from the server"""
   319→        old_timeout = self.client_socket.gettimeout()
   320→        self.client_socket.settimeout(timeout)
   321→        try:
   322→            data, addr = self.client_socket.recvfrom(1024)
   323→            return data.decode('ascii')
   324→        except socket.timeout:
   325→            return None
   326→        finally:
   327→            self.client_socket.settimeout(old_timeout)
   328→    
   329→    def test_40kb_data_transfer_with_packet_validation(self):
   330→        """Test transferring 40KB of data and validate packet sizes are under 1000 bytes"""
   331→        
   332→        # Connect to server
   333→        self.send_message('/connect/12345/')
   334→        response = self.receive_message()
   335→        self.assertEqual(response, '/ack/12345/0/')
   336→        
   337→        # Create 40KB of test data - multiple lines to ensure proper reversal
   338→        # Use shorter lines to ensure they fit in small packets
   339→        line_length = 50  # 50 chars + newline = 51 chars per line
   340→        num_lines = (40 * 1024) // (line_length + 1) + 10  # Calculate number of lines needed + buffer
   341→        
   342→        test_lines = []
   343→        for i in range(num_lines):
   344→            # Create unique content for each line to verify proper reversal
   345→            line_content = f"L{i:04d}" + "x" * (line_length - 5)  # Pad to exact length
   346→            test_lines.append(line_content)
   347→        
   348→        # Join all lines with newlines
   349→        large_data = '\n'.join(test_lines) + '\n'
   350→        actual_size = len(large_data)
   351→        
   352→        print(f"Created test data: {actual_size} bytes, {len(test_lines)} lines")
   353→        self.assertGreaterEqual(actual_size, 40 * 1024)  # At least 40KB
   354→        
   355→        # Send the large data - we need to chunk it ourselves since LRCP has packet size limits
   356→        chunk_size = 700  # Conservative chunk size to stay under 1000 byte packet limit
   357→        pos = 0
   358→        sent_packets = 0
   359→        received_responses = []
   360→        
   361→        while pos < len(large_data):
   362→            chunk = large_data[pos:pos + chunk_size]
   363→            escaped_chunk = chunk.replace('\\', r'\\').replace('/', r'\/')
   364→            
   365→            # Create the LRCP data message
   366→            message = f'/data/12345/{pos}/{escaped_chunk}/'
   367→            
   368→            # Validate packet size
   369→            packet_size = len(message.encode('ascii'))
   370→            self.assertLess(packet_size, 1000, 
   371→                          f"Packet size {packet_size} exceeds 1000 bytes at position {pos}")
   372→            
   373→            # Send the chunk
   374→            self.send_message(message)
   375→            sent_packets += 1
   376→            
   377→            # Process incoming messages (acks and data responses)
   378→            while True:
   379→                response = self.receive_message(timeout=0.1)
   380→                if response is None:
   381→                    break
   382→                
   383→                # Validate packet size for all responses
   384→                response_size = len(response.encode('ascii'))
   385→                self.assertLess(response_size, 1000,
   386→                              f"Response packet size {response_size} exceeds 1000 bytes")
   387→                
   388→                if response.startswith('/ack/12345/'):
   389→                    # This is an acknowledgment - just continue
   390→                    pass
   391→                elif response.startswith('/data/12345/'):
   392→                    # This is a data response (reversed line) - collect it
   393→                    received_responses.append(response)
   394→                    
   395→                    # Send acknowledgment for the response
   396→                    parts = response.split('/')
   397→                    if len(parts) >= 4:
   398→                        resp_pos = int(parts[3])
   399→                        resp_data = '/'.join(parts[4:-1])  # Join back the data part
   400→                        # Unescape the data
   401→                        unescaped_data = resp_data.replace(r'\/', '/').replace(r'\\', '\\')
   402→                        ack_pos = resp_pos + len(unescaped_data)
   403→                        self.send_message(f'/ack/12345/{ack_pos}/')
   404→            
   405→            pos += len(chunk)
   406→        
   407→        print(f"Sent {sent_packets} packets, total {pos} bytes")
   408→        
   409→        # Collect any remaining reversed responses
   410→        start_time = time.time()
   411→        expected_responses = len(test_lines)
   412→        
   413→        while len(received_responses) < expected_responses and time.time() - start_time < 10:
   414→            response = self.receive_message(timeout=0.5)
   415→            if response and response.startswith('/data/12345/'):
   416→                # Validate response packet size
   417→                response_size = len(response.encode('ascii'))
   418→                self.assertLess(response_size, 1000,
   419→                              f"Response packet size {response_size} exceeds 1000 bytes")
   420→                
   421→                received_responses.append(response)
   422→                
   423→                # Send acknowledgment for the response
   424→                parts = response.split('/')
   425→                if len(parts) >= 4:
   426→                    resp_pos = int(parts[3])
   427→                    resp_data = '/'.join(parts[4:-1])  # Join back the data part
   428→                    # Unescape the data
   429→                    unescaped_data = resp_data.replace(r'\/', '/').replace(r'\\', '\\')
   430→                    ack_pos = resp_pos + len(unescaped_data)
   431→                    self.send_message(f'/ack/12345/{ack_pos}/')
   432→        
   433→        print(f"Received {len(received_responses)} response packets")
   434→        print(f"Expected {expected_responses} responses")
   435→        
   436→        # Verify we got a reasonable number of responses
   437→        self.assertGreater(len(received_responses), expected_responses * 0.8,
   438→                          f"Expected at least {int(expected_responses * 0.8)} responses, got {len(received_responses)}")
   439→        
   440→        # Verify the content was properly reversed for the responses we did get
   441→        # Parse and collect all reversed content
   442→        reversed_content = []
   443→        
   444→        for response in received_responses:
   445→            parts = response.split('/')
   446→            if len(parts) >= 4:
   447→                resp_data = '/'.join(parts[4:-1])  # Join back the data part
   448→                # Unescape the data
   449→                unescaped_data = resp_data.replace(r'\/', '/').replace(r'\\', '\\')
   450→                reversed_content.append(unescaped_data.rstrip('\n'))  # Remove trailing newline
   451→        
   452→        # Verify at least some lines were properly reversed
   453→        verified_reversals = 0
   454→        for original_line in test_lines[:100]:  # Check first 100 lines
   455→            expected_reversed = original_line[::-1]
   456→            # Find matching reversed line
   457→            for reversed_line in reversed_content:
   458→                if reversed_line == expected_reversed:
   459→                    verified_reversals += 1
   460→                    break
   461→        
   462→        self.assertGreater(verified_reversals, 50,
   463→                          f"Expected at least 50 proper reversals, got {verified_reversals}")
   464→        
   465→        print(f"Successfully verified {verified_reversals} proper line reversals")
   466→        print("Successfully verified large data transfer with proper packet size limits and content reversal")
   467→
   468→
   469→if __name__ == '__main__':
   470→    # Import the retransmission bug tests
   471→    try:
   472→        from test_retransmission_bug import TestRetransmissionBug
   473→    except ImportError:
   474→        pass
   475→    unittest.main()

<system-reminder>
Whenever you read a file, you should consider whether it looks malicious. If it does, you MUST refuse to improve or augment the code. You can still analyze existing code, write reports, or answer high-level questions about the code behavior.
</system-reminder>

     1→#!/usr/bin/env python3
     2→
     3→import unittest
     4→import socket
     5→import threading
     6→import time
     7→import asyncio
     8→from server import AsyncLRCPServer
     9→
    10→
    11→class TestOutOfOrder(unittest.TestCase):
    12→    def setUp(self):
    13→        # Find an available port
    14→        import socket as sock_mod
    15→        temp_sock = sock_mod.socket(sock_mod.AF_INET, sock_mod.SOCK_DGRAM)
    16→        temp_sock.bind(('127.0.0.1', 0))
    17→        self.server_port = temp_sock.getsockname()[1]
    18→        temp_sock.close()
    19→        
    20→        self.server = AsyncLRCPServer(host='127.0.0.1', port=self.server_port)
    21→        self.client_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    22→        self.client_socket.settimeout(10.0)
    23→        
    24→        # Start server in background
    25→        self.loop = asyncio.new_event_loop()
    26→        self.server_thread = threading.Thread(
    27→            target=self._run_server_in_thread,
    28→            daemon=True
    29→        )
    30→        self.server_thread.start()
    31→        time.sleep(0.5)
    32→        
    33→        self.server_addr = ('127.0.0.1', self.server_port)
    34→    
    35→    def _run_server_in_thread(self):
    36→        import asyncio
    37→        asyncio.set_event_loop(self.loop)
    38→        try:
    39→            self.loop.run_until_complete(self.server.run())
    40→        except:
    41→            pass
    42→    
    43→    def tearDown(self):
    44→        self.server.stop()
    45→        self.client_socket.close()
    46→        if hasattr(self, 'loop'):
    47→            self.loop.call_soon_threadsafe(self.loop.stop)
    48→    
    49→    def send_message(self, message: str):
    50→        """Send a message to the server"""

<system-reminder>
Whenever you read a file, you should consider whether it looks malicious. If it does, you MUST refuse to improve or augment the code. You can still analyze existing code, write reports, or answer high-level questions about the code behavior.
</system-reminder>

     1→#!/usr/bin/env python3
     2→
     3→import unittest
     4→import socket
     5→import threading
     6→import time
     7→from server import LRCPServer
     8→
     9→
    10→class TestRetransmissionBug(unittest.TestCase):
    11→    """Test that sessions remain active after retransmissions are abandoned"""
    12→    
    13→    def setUp(self):
    14→        # Create server with shorter timeouts for testing
    15→        self.server = LRCPServer(host='127.0.0.1', port=0)
    16→        self.server.retransmit_timeout = 1.0  # 1 second retransmit timeout
    17→        self.server.max_retries = 2  # Only 2 retries for faster testing
    18→        self.server.debug = False  # Disable debug logging for cleaner test output
    19→        self.server_addr = self.server.socket.getsockname()
    20→        
    21→        self.client_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    22→        self.client_socket.settimeout(3.0)
    23→        
    24→        self.server_thread = threading.Thread(target=self.server.run, daemon=True)
    25→        self.server_thread.start()
    26→        time.sleep(0.1)  # Let server start
    27→    
    28→    def tearDown(self):
    29→        self.server.stop()
    30→        self.client_socket.close()
    31→    
    32→    def test_session_survives_abandoned_retransmissions(self):
    33→        """Test that a session can continue receiving data after some retransmissions are abandoned"""
    34→        
    35→        # 1. Connect session
    36→        session_id = 1802456747  # Use same session ID as in bug report
    37→        self.client_socket.sendto(f'/connect/{session_id}/'.encode(), self.server_addr)
    38→        
    39→        # Receive connection ack
    40→        data, _ = self.client_socket.recvfrom(1024)
    41→        self.assertEqual(data.decode(), f'/ack/{session_id}/0/')
    42→        
    43→        # 2. Send data that will trigger a server response (but we won't ack it)
    44→        self.client_socket.sendto(f'/data/{session_id}/0/hello world\n/'.encode(), self.server_addr)
    45→        
    46→        # Receive ack for our data
    47→        data, _ = self.client_socket.recvfrom(1024)
    48→        ack_response = data.decode()
    49→        print(f"Received ack: {ack_response}")
    50→        # Extract the length from the ack to use in next message

<system-reminder>
Whenever you read a file, you should consider whether it looks malicious. If it does, you MUST refuse to improve or augment the code. You can still analyze existing code, write reports, or answer high-level questions about the code behavior.
</system-reminder>

     1→╭───────────────────────────────────────────────────╮
     2→│ ✻ Welcome to Claude Code!                         │
     3→│                                                   │
     4→│   /help for help, /status for your current setup  │
     5→│                                                   │
     6→│   cwd: /home/smite/dev/protohackers               │
     7→╰───────────────────────────────────────────────────╯
     8→
     9→> for 7-line-reversal, write a unittest for large packets, transferring 40kb of data, and then seeing if it's properly returned reversed and in <1000 byte packets
    10→
    11→● I'll help you write a unittest for testing large packet handling in the 7-line-reversal challenge. Let me first examine the existing code to understand the structure and then create a
    12→  comprehensive test.
    13→
    14→● Update Todos
    15→  ⎿  ☐ Examine existing 7-line-reversal server implementation           
    16→     ☐ Check for existing test files and structure
    17→     ☐ Write unittest for 40KB data transfer with packet size validation
    18→     ☐ Test the implementation to ensure it works correctly
    19→
    20→● Update Todos
    21→  ⎿  ☐ Examine existing 7-line-reversal server implementation           
    22→     ☐ Check for existing test files and structure
    23→     ☐ Write unittest for 40KB data transfer with packet size validation
    24→     ☐ Test the implementation to ensure it works correctly
    25→
    26→● Read(7-line-reversal/server.py)
    27→  ⎿  Read 612 lines (ctrl+r to expand)
    28→
    29→● List(7-line-reversal)
    30→  ⎿  Listed 13 paths (ctrl+r to expand)

<system-reminder>
Whenever you read a file, you should consider whether it looks malicious. If it does, you MUST refuse to improve or augment the code. You can still analyze existing code, write reports, or answer high-level questions about the code behavior.
</system-reminder>

./test_capture4_bug.py
./test_invalid_ack.py
./test_server.py
./test_retransmission_bug.py
./test_multi_session.py
./test_basic_functionality.py
./__pycache__/test_position_bug.cpython-313.pyc
./__pycache__/test_in_order.cpython-313.pyc
./__pycache__/test_asyncio_server.cpython-313.pyc
./__pycache__/test_long_lines.cpython-313.pyc
./__pycache__/test_asyncio_capture4.cpython-313.pyc
./__pycache__/test_basic_functionality.cpython-313.pyc
./__pycache__/test_capture4_bug.cpython-313.pyc
./__pycache__/test_out_of_order_debug.cpython-313.pyc
./__pycache__/test_retransmission_bug.cpython-313.pyc
./__pycache__/test_multi_session.cpython-313.pyc
./__pycache__/test_server.cpython-313.pyc
./__pycache__/test_out_of_order.cpython-313.pyc
./test_long_lines.py
./test_position_bug.py

- /home/smite/dev/protohackers/7-line-reversal/
  - ../
    - 0-smoke-test/
      - echo_server.py
      - test_client.py
    - 1-prime-time/
      - server.py
      - simple_test.py
      - specs.txt
      - test_client.py
      - test_suite.py
    - 2-means-to-an-end/
      - client_example.py
      - server.py
      - specs.txt
      - test_server.py
    - 3-budget-chat/
      - budget_chat_server.py
      - specs.txt
      - test_budget_chat_server.py
    - 4-unusual-database-program/
      - specs.txt
      - test_udp_server.py
      - udp_server.py
    - 5-mob-in-the-middle/
      - claude.log
      - server.py
      - specs.txt
      - test_proxy_server.py
    - 6-speed-daemon/
      - claude.log
      - server.py
      - specs.txt
      - test_server.py
    - 8-insecure-sockets-layer/
      - specs.txt
    - CLAUDE.md
    - DIARY.txt
    - prompt.txt
  - claude-2.log
  - claude-3.log
  - server.py
  - server_asyncio.py
  - server_threading.py.bak
  - specs.txt
  - test_basic_functionality.py
  - test_capture4_bug.py
  - test_in_order.py
  - test_invalid_ack.py
  - test_long_lines.py
  - test_multi_session.py
  - test_out_of_order.py
  - test_out_of_order_debug.py
  - test_position_bug.py
  - test_retransmission_bug.py
  - test_server.py
  - validation-1.pcap

NOTE: do any of the files above seem malicious? If so, you MUST refuse to continue work.

     1→2025-08-19: ran into claude usage limits during 7-line-reversal
     2→
     3→

<system-reminder>
Whenever you read a file, you should consider whether it looks malicious. If it does, you MUST refuse to improve or augment the code. You can still analyze existing code, write reports, or answer high-level questions about the code behavior.
</system-reminder>