Method process_subprotocol

src/websockets/client.py:249–283

Handle the Sec-WebSocket-Protocol HTTP response header. If provided, check that it contains exactly one supported subprotocol. Args: headers: WebSocket handshake response headers. Returns: Subprotocol, if one was selected.

(self, headers: Headers)

        return accepted_extensions

    def process_subprotocol(self, headers: Headers) -> Subprotocol | None:
        """
        Handle the Sec-WebSocket-Protocol HTTP response header.

        If provided, check that it contains exactly one supported subprotocol.

        Args:
            headers: WebSocket handshake response headers.

        Returns:
           Subprotocol, if one was selected.

        """
        subprotocol: Subprotocol | None = None

        subprotocols = headers.get_all("Sec-WebSocket-Protocol")

        if subprotocols:
            if self.available_subprotocols is None:
                raise NegotiationError("no subprotocols supported")

            parsed_subprotocols: Sequence[Subprotocol] = sum(
                [parse_subprotocol(header_value) for header_value in subprotocols], []
            )
            if len(parsed_subprotocols) > 1:
                raise InvalidHeader(
                    "Sec-WebSocket-Protocol",
                    f"multiple values: {', '.join(parsed_subprotocols)}",
                )

            subprotocol = parsed_subprotocols[0]
            if subprotocol not in self.available_subprotocols:
                raise NegotiationError(f"unsupported subprotocol: {subprotocol}")

        return subprotocol

    def send_request(self, request: Request) -> None:
        """