Isolate TCP message framing

server/tcp_transport.py

@@ -0,0 +1,55 @@
+from __future__ import annotations
+
+import socket
+
+from packet_codec import MAX_MESSAGE_BYTES
+
+
+class TcpFramingError(ValueError):
+    pass
+
+
+def frame_message(payload: bytes | bytearray | memoryview) -> bytes:
+    raw = bytes(payload)
+    if len(raw) > MAX_MESSAGE_BYTES:
+        raise TcpFramingError("TCP message exceeds maximum message size")
+    if b"\n" in raw or b"\r" in raw:
+        raise TcpFramingError("transport-neutral payload must not contain raw line delimiters")
+    return raw + b"\n"
+
+
+def send_message(connection: socket.socket, payload: bytes | bytearray | memoryview) -> None:
+    connection.sendall(frame_message(payload))
+
+
+class LineMessageBuffer:
+    def __init__(self) -> None:
+        self._buffer = bytearray()
+
+    @property
+    def buffered_bytes(self) -> int:
+        return len(self._buffer)
+
+    def clear(self) -> None:
+        self._buffer.clear()
+
+    def feed(self, chunk: bytes | bytearray | memoryview) -> list[bytes]:
+        raw = bytes(chunk)
+        if not raw:
+            return []
+        self._buffer.extend(raw)
+        messages: list[bytes] = []
+        while True:
+            newline = self._buffer.find(b"\n")
+            if newline < 0:
+                break
+            if newline > MAX_MESSAGE_BYTES:
+                raise TcpFramingError("TCP message exceeds maximum message size")
+            message = bytes(self._buffer[:newline])
+            del self._buffer[: newline + 1]
+            if message.endswith(b"\r"):
+                message = message[:-1]
+            messages.append(message)
+        if len(self._buffer) > MAX_MESSAGE_BYTES:
+            raise TcpFramingError("unterminated TCP message exceeds maximum message size")
+        return messages