Function readWebSocketFrame

src/Server/WebTerminalRequestHandler.cpp:170–258

Read a single WebSocket frame from the socket. If deadline_ns is non-zero, abort when the monotonic clock exceeds it. `max_payload_size` caps the advertised payload length and is set tighter for pre-auth frames to prevent a single unauthenticated client from forcing the server to allocate up to 16 MiB before any credentials have been checked.

/// forcing the server to allocate up to 16 MiB before any credentials have
/// been checked.
WebSocketFrame readWebSocketFrame(Poco::Net::StreamSocket & socket, UInt64 deadline_ns = 0, uint64_t max_payload_size = 16 * 1024 * 1024)
{
    WebSocketFrame frame;
    uint8_t header[2];

    if (!readExact(socket, reinterpret_cast<char *>(header), 2, deadline_ns))
        return frame;

    frame.fin = (header[0] & 0x80) != 0;
    frame.opcode = header[0] & 0x0F;

    /// RSV1/RSV2/RSV3 must be zero (no extensions negotiated)
    if (header[0] & 0x70)
    {
        frame.protocol_error = true;
        return frame;
    }

    /// Reject reserved opcodes per RFC 6455 Section 5.2
    if ((frame.opcode >= 0x03 && frame.opcode <= 0x07) || frame.opcode >= 0x0B)
    {
        frame.protocol_error = true;
        return frame;
    }

    bool masked = (header[1] & 0x80) != 0;
    uint64_t payload_len = header[1] & 0x7F;

    /// RFC 6455: client-to-server frames MUST be masked
    if (!masked)
    {
        frame.protocol_error = true;
        return frame;
    }

    /// Control frames (opcode >= 0x08) must have FIN set and payload <= 125
    if (frame.opcode >= 0x08)
    {
        if (!frame.fin || payload_len > 125)
        {
            frame.protocol_error = true;
            return frame;
        }
    }

    if (payload_len == 126)
    {
        uint8_t ext[2];
        if (!readExact(socket, reinterpret_cast<char *>(ext), 2, deadline_ns))
            return frame;
        payload_len = (static_cast<uint64_t>(ext[0]) << 8) | ext[1];
    }
    else if (payload_len == 127)
    {
        uint8_t ext[8];
        if (!readExact(socket, reinterpret_cast<char *>(ext), 8, deadline_ns))
            return frame;
        payload_len = 0;