protohackers: Insecure Sockets Layer Server Implementation Complete

- /home/smite/dev/protohackers/
  - 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
  - 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
  - 8-insecure-sockets-layer/
    - specs.txt
  - CLAUDE.md
  - DIARY.txt
  - prompt.txt

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

     1→#!/usr/bin/env python3
     2→import socket
     3→import threading
     4→import sys
     5→
     6→class EchoServer:
     7→    def __init__(self, host='localhost', port=8080):
     8→        self.host = host
     9→        self.port = port
    10→        self.server_socket = None
    11→        
    12→    def handle_client(self, client_socket, client_address):
    13→        try:
    14→            print(f"Client connected: {client_address}")
    15→            while True:
    16→                data = client_socket.recv(1024)
    17→                if not data:
    18→                    break
    19→                client_socket.send(data)
    20→        except Exception as e:
    21→            print(f"Error handling client {client_address}: {e}")
    22→        finally:
    23→            client_socket.close()
    24→            print(f"Client disconnected: {client_address}")
    25→    
    26→    def start(self):
    27→        try:
    28→            self.server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    29→            self.server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    30→            self.server_socket.bind((self.host, self.port))
    31→            self.server_socket.listen(5)
    32→            
    33→            print(f"Echo server listening on {self.host}:{self.port}")
    34→            print("Press Ctrl+C to stop the server")
    35→            
    36→            while True:
    37→                client_socket, client_address = self.server_socket.accept()
    38→                client_thread = threading.Thread(
    39→                    target=self.handle_client, 
    40→                    args=(client_socket, client_address)
    41→                )
    42→                client_thread.daemon = True
    43→                client_thread.start()
    44→                
    45→        except KeyboardInterrupt:
    46→            print("\nShutting down server...")
    47→        except Exception as e:
    48→            print(f"Server error: {e}")
    49→        finally:
    50→            if self.server_socket:
    51→                self.server_socket.close()
    52→
    53→def main():
    54→    port = 8080
    55→    if len(sys.argv) > 1:
    56→        try:
    57→            port = int(sys.argv[1])
    58→        except ValueError:
    59→            print("Invalid port number. Using default port 8080.")
    60→    
    61→    server = EchoServer(host='0.0.0.0', port=port)
    62→    server.start()
    63→
    64→if __name__ == "__main__":
    65→    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→import json
     3→import socket
     4→import threading
     5→import sys
     6→import math
     7→import os
     8→
     9→DEBUG = os.environ.get('DEBUG', '').lower() in ('1', 'true', 'yes')
    10→
    11→def is_prime(n):
    12→    if not isinstance(n, (int, float)):
    13→        return False
    14→    
    15→    if n != int(n):
    16→        return False
    17→    
    18→    n = int(n)
    19→    
    20→    if n < 2:
    21→        return False
    22→    
    23→    if n == 2:
    24→        return True
    25→    
    26→    if n % 2 == 0:
    27→        return False
    28→    
    29→    for i in range(3, int(math.sqrt(n)) + 1, 2):
    30→        if n % i == 0:
    31→            return False
    32→    
    33→    return True
    34→
    35→def handle_client(client_socket, client_address, debug=False):
    36→    print(f"Connected to {client_address}")
    37→    
    38→    try:
    39→        buffer = ""
    40→        while True:
    41→            data = client_socket.recv(1024).decode('utf-8')
    42→            if not data:
    43→                break
    44→            
    45→            if debug:
    46→                print(f"[{client_address}] RECV: {repr(data)}")
    47→            
    48→            buffer += data
    49→            
    50→            while '\n' in buffer:
    51→                line, buffer = buffer.split('\n', 1)
    52→                
    53→                if debug:
    54→                    print(f"[{client_address}] IN: {repr(line)}")
    55→                
    56→                try:
    57→                    request = json.loads(line)
    58→                    
    59→                    if not isinstance(request, dict):
    60→                        raise ValueError("Not a JSON object")
    61→                    
    62→                    if request.get("method") != "isPrime":
    63→                        raise ValueError("Invalid method")
    64→                    
    65→                    if "number" not in request:
    66→                        raise ValueError("Missing number field")
    67→                    
    68→                    number = request["number"]
    69→                    if not isinstance(number, (int, float)) or isinstance(number, bool):
    70→                        raise ValueError("Number field is not a number")
    71→                    
    72→                    prime_result = is_prime(number)
    73→                    
    74→                    response = {
    75→                        "method": "isPrime",
    76→                        "prime": prime_result
    77→                    }
    78→                    
    79→                    response_json = json.dumps(response) + '\n'
    80→                    if debug:
    81→                        print(f"[{client_address}] OUT: {repr(response_json.rstrip())}")
    82→                    client_socket.send(response_json.encode('utf-8'))
    83→                    
    84→                except Exception as e:
    85→                    if debug:
    86→                        print(f"[{client_address}] ERROR: {e}")
    87→                    malformed_response = "malformed\n"
    88→                    if debug:
    89→                        print(f"[{client_address}] OUT: {repr(malformed_response.rstrip())}")
    90→                    client_socket.send(malformed_response.encode('utf-8'))
    91→                    print(f"Malformed request from {client_address}, disconnecting")
    92→                    break
    93→    
    94→    except Exception as e:
    95→        print(f"Error handling client {client_address}: {e}")
    96→    
    97→    finally:
    98→        client_socket.close()
    99→        print(f"Disconnected from {client_address}")
   100→
   101→def main():
   102→    host = '0.0.0.0'
   103→    port = 8080
   104→    debug = DEBUG
   105→    
   106→    if len(sys.argv) > 1:
   107→        port = int(sys.argv[1])
   108→    
   109→    if debug:
   110→        print("Debug logging enabled")
   111→    
   112→    server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
   113→    server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
   114→    
   115→    try:
   116→        server_socket.bind((host, port))
   117→        server_socket.listen(5)
   118→        print(f"Prime Time server listening on {host}:{port}")
   119→        
   120→        while True:
   121→            client_socket, client_address = server_socket.accept()
   122→            client_thread = threading.Thread(
   123→                target=handle_client,
   124→                args=(client_socket, client_address, debug)
   125→            )
   126→            client_thread.daemon = True
   127→            client_thread.start()
   128→    
   129→    except KeyboardInterrupt:
   130→        print("\nServer shutting down...")
   131→    except Exception as e:
   132→        print(f"Server error: {e}")
   133→    finally:
   134→        server_socket.close()
   135→
   136→if __name__ == "__main__":
   137→    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→Use python async io. When testing bugs, write a proper unittest that remains instead of a one-time test and is then deleted. When fixing protocol behaviour, trying to write a test confirming the problem before fixing it, and then confirm it's fixed.
     2→

<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/0-smoke-test/test_client.py
/home/smite/dev/protohackers/1-prime-time/test_client.py
/home/smite/dev/protohackers/1-prime-time/test_suite.py
/home/smite/dev/protohackers/2-means-to-an-end/test_server.py
/home/smite/dev/protohackers/3-budget-chat/test_budget_chat_server.py
/home/smite/dev/protohackers/4-unusual-database-program/test_udp_server.py
/home/smite/dev/protohackers/5-mob-in-the-middle/test_proxy_server.py
/home/smite/dev/protohackers/6-speed-daemon/test_server.py
/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→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:

<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→The Elves at the North Pole have been so busy saving Christmas that they haven't found time to properly secure the work orders for the Christmas toy workshop! They've invented a quick and dirty obfuscation scheme to obscure the data from prying eyes.
     2→
     3→Warning: This protocol is irrecoverably flawed. Don't use it in real life. The Elves are dumb, but you don't have to be. Read more about rolling your own crypto.
     4→
     5→Application layer
     6→At the start of a session, a client connects using TCP and sends a "cipher spec", and all further communication over the session (both to and from the server) is obfuscated using the cipher spec.
     7→
     8→A client request is a line of ASCII text (terminated by a single newline character) containing a comma-separated list of toys to make, like so:
     9→
    10→10x toy car,15x dog on a string,4x inflatable motorcycle
    11→To prioritise work in the toy workshop, the server must find out which toy from the request they need to make the most copies of, and then send that toy back, also terminated with an ASCII newline character, like so:
    12→
    13→15x dog on a string
    14→There can be multiple requests per session.
    15→
    16→Obfuscation layer
    17→All communication is obfuscated by the "Insecure Sockets Layer", using the cipher spec supplied by the client when it first connected.
    18→
    19→Cipher spec
    20→The cipher spec describes the series of operations that were used to obfuscate the data. The server must apply the same cipher spec to encode its response stream. The server must apply the inverse of the cipher spec to decode the request stream.
    21→
    22→The cipher spec is represented as a series of operations, with the operation types encoded by a single byte (and for 02 and 04, another byte encodes the operand), ending with a 00 byte, as follows:
    23→
    24→00: End of cipher spec.
    25→
    26→01: reversebits: Reverse the order of bits in the byte, so the least-significant bit becomes the most-significant bit, the 2nd-least-significant becomes the 2nd-most-significant, and so on.
    27→
    28→02 N: xor(N): XOR the byte by the value N. Note that 0 is a valid value for N.
    29→
    30→03: xorpos: XOR the byte by its position in the stream, starting from 0.
    31→
    32→04 N: add(N): Add N to the byte, modulo 256. Note that 0 is a valid value for N, and addition wraps, so that 255+1=0, 255+2=1, and so on.
    33→
    34→05: addpos: Add the position in the stream to the byte, modulo 256, starting from 0. Addition wraps, so that 255+1=0, 255+2=1, and so on.
    35→
    36→For the purposes of the xorpos and addpos operations, note that there is a separate stream position counter for the client-sent and server-sent streams, with each one starting at 0, and the counter is not reset to 0 at the end of each request or response.
    37→
    38→No-op ciphers
    39→If a client tries to use a cipher that leaves every byte of input unchanged, the server must immediately disconnect without sending any data back. Examples of no-op ciphers include (but are not limited to):
    40→
    41→empty cipher spec (00)
    42→xor(0) (02 00 00)
    43→xor(X),xor(X) for any X (e.g. 02 ab 02 ab 00)
    44→reversebits,reversebits (01 01 00)
    45→xor(A),xor(B),xor(C), where A|B=C (e.g. 02 a0 02 0b 02 ab 00)
    46→Example cipher specs
    47→xor(1),reversebits
    48→The cipher spec xor(1),reversebits would be represented in hexadecimal as 02 01 01 00:
    49→
    50→02 01     xor(1)
    51→01        reversebits
    52→00        end of cipher spec
    53→It would encode the message "hello" in hexadecimal from 68 65 6c 6c 6f to 96 26 b6 b6 76:
    54→
    55→pos:           0  1  2  3  4
    56→message:       h  e  l  l  o
    57→hex:          68 65 6c 6c 6f
    58→
    59→xor(1):       69 64 6d 6d 6e
    60→reversebits:  96 26 b6 b6 76
    61→addpos,addpos
    62→The cipher spec addpos,addpos would be represented in hexadecimal as 05 05 00:
    63→
    64→05        addpos
    65→05        addpos
    66→00        end of cipher spec
    67→It would encode the message "hello" in hexadecimal from 68 65 6c 6c 6f to 68 67 70 72 77:
    68→
    69→pos:      0  1  2  3  4
    70→message:  h  e  l  l  o
    71→hex:     68 65 6c 6c 6f
    72→
    73→addpos:  68 66 6e 6f 73
    74→addpos:  68 67 70 72 77
    75→Example session
    76→Example session at application layer ("-->" denotes lines from the server to the client, and "<--" denotes lines from the client to the server):
    77→
    78→<-- 4x dog,5x car
    79→--> 5x car
    80→<-- 3x rat,2x cat
    81→--> 3x rat
    82→The same session after obfuscation, in hexadecimal, might look like this, with cipher spec xor(123),addpos,reversebits ("-->" denotes data from the server to the client, and "<--" denotes data from the client to the server):
    83→
    84→<-- 02 7b 05 01 00                              xor(123),addpos,reversebits
    85→<-- f2 20 ba 44 18 84 ba aa d0 26 44 a4 a8 7e   4x dog,5x car\n
    86→--> 72 20 ba d8 78 70 ee                        5x car\n
    87→<-- 6a 48 d6 58 34 44 d6 7a 98 4e 0c cc 94 31   3x rat,2x cat\n
    88→--> f2 d0 26 c8 a4 d8 7e                        3x rat\n
    89→Limits
    90→Make sure you support at least 10 simultaneous clients.
    91→
    92→Clients won't send lines longer than 5000 characters.
    93→
    94→Clients won't send cipher specs whose encoding is longer than 80 bytes.
    95→
    96→Clients won't try to use illegal cipher specs (e.g. 07 00 is illegal, because 07 is not a valid cipher spec operation).
    97→
    98→Clients won't send requests that are not a comma-separated list of toys, starting with an ASCII-formatted integer followed by an "x" character.
    99→
   100→If multiple toys share the maximum number, you can break the tie arbitrarily.
   101→
   102→There will always be fewer than 2^31 copies required for any given toy.
   103→
   104→The empty request is not a valid request.
   105→
   106→As the Elves are so busy, they don't have time to worry about pesky edge cases. In response to invalid input the server is free to do nothing, crash, or vanish in a puff of logic.

<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>

Command timed out after 2m 0.0s test_add_operation (test_server.TestCipherSpec.test_add_operation)
Test add operation ... ok
test_addpos_double (test_server.TestCipherSpec.test_addpos_double)
Test the example from specs: addpos,addpos ... ok
test_addpos_operation (test_server.TestCipherSpec.test_addpos_operation)
Test addpos operation ... ok
test_combined_operations (test_server.TestCipherSpec.test_combined_operations)
Test the example from specs: xor(1),reversebits ... ok
test_no_op_detection (test_server.TestCipherSpec.test_no_op_detection)
Test no-op cipher detection ... ok
test_reversebits (test_server.TestCipherSpec.test_reversebits)
Test reversebits operation ... ok
test_xor_operation (test_server.TestCipherSpec.test_xor_operation)
Test xor operation ... ok
test_xorpos_operation (test_server.TestCipherSpec.test_xorpos_operation)
Test xorpos operation ... ok
test_parse_combined (test_server.TestCipherSpecParsing.test_parse_combined)
Test parsing combined operations ... ok
test_parse_empty_spec (test_server.TestCipherSpecParsing.test_parse_empty_spec)
Test parsing empty cipher spec ... ok
test_parse_reversebits (test_server.TestCipherSpecParsing.test_parse_reversebits)
Test parsing reversebits operation ... ok
test_parse_xor (test_server.TestCipherSpecParsing.test_parse_xor)
Test parsing xor operation ... ok
test_simple_session (test_server.TestServerIntegration.test_simple_session)
Test a simple session with cipher ... /usr/lib/python3.13/unittest/case.py:606: RuntimeWarning: coroutine 'TestServerIntegration.test_simple_session' was never awaited
  if method() is not None:
RuntimeWarning: Enable tracemalloc to get the object allocation traceback
/usr/lib/python3.13/unittest/case.py:707: DeprecationWarning: It is deprecated to return a value that is not None from a test case (<bound method TestServerIntegration.test_simple_session of <test_server.TestServerIntegration testMethod=test_simple_session>>)
  return self.run(*args, **kwds)
ok
test_simple_session_sync (test_server.TestServerIntegration.test_simple_session_sync)
Synchronous wrapper for async test ...

The file /home/smite/dev/protohackers/8-insecure-sockets-layer/test_server.py has been updated. Here's the result of running `cat -n` on a snippet of the edited file:
   181→        # Get the actual port the server is listening on
   182→        server_socket = self.server.server.sockets[0]
   183→        return server_socket.getsockname()
   184→    
   185→    def test_simple_session_sync(self):
   186→        """Test a simple session with cipher"""
   187→        async def test_session():
   188→            host, port = await self.start_test_server()
   189→            
   190→            reader, writer = await asyncio.open_connection(host, port)
   191→            
   192→            try:
   193→                # Send cipher spec: xor(1) -> 02 01 00
   194→                writer.write(b'\x02\x01\x00')
   195→                await writer.drain()
   196→                
   197→                # Send request: "4x dog,5x car\n"
   198→                request = "4x dog,5x car\n"
   199→                request_bytes = request.encode('ascii')
   200→                
   201→                # Apply cipher: xor(1)
   202→                cipher = CipherSpec([(2, 0x01)])
   203→                encoded_request = cipher.encode(request_bytes)
   204→                
   205→                writer.write(encoded_request)
   206→                await writer.drain()
   207→                
   208→                # Read response
   209→                response_data = await reader.readline()
   210→                
   211→                # Decode response
   212→                decoded_response = cipher.decode(response_data)
   213→                response = decoded_response.decode('ascii')
   214→                
   215→                self.assertEqual(response, "5x car\n")
   216→                
   217→            finally:
   218→                writer.close()
   219→                await writer.wait_closed()
   220→        
   221→        asyncio.run(test_session())
   222→
   223→if __name__ == '__main__':
   224→    unittest.main()

test_add_operation (test_server.TestCipherSpec.test_add_operation)
Test add operation ... ok
test_addpos_double (test_server.TestCipherSpec.test_addpos_double)
Test the example from specs: addpos,addpos ... ok
test_addpos_operation (test_server.TestCipherSpec.test_addpos_operation)
Test addpos operation ... ok
test_combined_operations (test_server.TestCipherSpec.test_combined_operations)
Test the example from specs: xor(1),reversebits ... ok
test_no_op_detection (test_server.TestCipherSpec.test_no_op_detection)
Test no-op cipher detection ... ok
test_reversebits (test_server.TestCipherSpec.test_reversebits)
Test reversebits operation ... ok
test_xor_operation (test_server.TestCipherSpec.test_xor_operation)
Test xor operation ... ok
test_xorpos_operation (test_server.TestCipherSpec.test_xorpos_operation)
Test xorpos operation ... ok

----------------------------------------------------------------------
Ran 8 tests in 0.001s

OK

<status>completed</status>

<exit_code>0</exit_code>

<stderr>
Traceback (most recent call last):
  File "/home/smite/dev/protohackers/8-insecure-sockets-layer/server.py", line 306, in <module>
    asyncio.run(main())
    ~~~~~~~~~~~^^^^^^^^
  File "/usr/lib/python3.13/asyncio/runners.py", line 195, in run
    return runner.run(main)
           ~~~~~~~~~~^^^^^^
  File "/usr/lib/python3.13/asyncio/runners.py", line 118, in run
    return self._loop.run_until_complete(task)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/usr/lib/python3.13/asyncio/base_events.py", line 719, in run_until_complete
    return future.result()
           ~~~~~~~~~~~~~^^
  File "/home/smite/dev/protohackers/8-insecure-sockets-layer/server.py", line 300, in main
    await server.run()
  File "/home/smite/dev/protohackers/8-insecure-sockets-layer/server.py", line 267, in run
    self.server = await asyncio.start_server(
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<3 lines>...
    )
    ^
  File "/usr/lib/python3.13/asyncio/streams.py", line 84, in start_server
    return await loop.create_server(factory, host, port, **kwds)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.13/asyncio/base_events.py", line 1616, in create_server
    raise OSError(err.errno, msg) from None
OSError: [Errno 98] error while attempting to bind on address ('0.0.0.0', 9999): [errno 98] address already in use
</stderr>

<timestamp>2025-08-21T08:14:37.148Z</timestamp>

Testing cipher operations...
xor(1),reversebits 'hello': 9626b6b676 (expected: 9626b6b676)
Decoded back: 'hello'
addpos,addpos 'hello': 6867707277 (expected: 6867707277)
Decoded back: 'hello'
All cipher tests passed!

Testing toy parsing...
'4x dog,5x car' -> '5x car'
Complex toys -> '15x dog on a string'
Toy parsing tests passed!

Testing no-op detection...
Empty cipher correctly detected as no-op
xor(0) correctly detected as no-op
xor(X),xor(X) correctly detected as no-op
xor(1) correctly detected as non-no-op
No-op detection tests passed!

✅ All tests passed! Server implementation looks correct.

The file /home/smite/dev/protohackers/8-insecure-sockets-layer/server.py has been updated. Here's the result of running `cat -n` on a snippet of the edited file:
   269→            self.host,
   270→            self.port
   271→        )
   272→        
   273→        addr_info = self.server.sockets[0].getsockname()
   274→        actual_port = addr_info[1]
   275→        if __name__ == '__main__':
   276→            print(f"Insecure Sockets Layer server listening on {self.host}:{actual_port}")
   277→        
   278→        try:
   279→            await self.server.serve_forever()
   280→        except asyncio.CancelledError: