Websockets: send multi frames

[mikeduglas]

I did this

I want to send multiple frames (not fragments).
AFAIK 1st frame must not have CURLWS_CONT bit set and FIN bit aslo must be 0. All other frames must have CURLWS_CONT bit set, also last frame must have FIN bit set.

Now, in ws_packethead function, FIN bit is always set to 1 if CURLWS_CONT bit is not set. So the server gets only first frame and ignores all other frames.

I expected the following

curl/libcurl version

7.87.1-DEV

operating system

Windows 11

[mikeduglas]

Seems I found a bug in ws_packethead, see the comment inside the final "else" clause, now I'm able to send multi frame packets.

  if(!(flags & CURLWS_CONT)) {
    /* if not marked as continuing, assume this is the final fragment */
    firstbyte |= WSBIT_FIN | opcode;
    ws->ws.contfragment = FALSE;
    infof(data, "WS: if not marked as continuing, assume this is the final fragment");
  }
  else if(ws->ws.contfragment) {
    /* the previous fragment was not a final one and this isn't either, keep a
       CONT opcode and no FIN bit */
    firstbyte |= WSBIT_OPCODE_CONT;
    infof(data, "WS: the previous fragment was not a final one and this isn't either, keep a CONT opcode and no FIN bit");
  }
  else {
      firstbyte = opcode;   // <--- I added this line, otherwise 1st frame loses the opcode (TEXT or BINARY) and is always sent as continuation frame (firstbyte is 0 that means WSBIT_OPCODE_CONT )
      ws->ws.contfragment = TRUE;
    infof(data, "WS: ws->ws.contfragment = TRUE;");
  }

[mikeduglas]

Above solution is incomplete, last frame must be sent with CONT opcode, so here is the code that seems to work properly:

  if(!(flags & CURLWS_CONT)) {
    if (!ws->ws.contfragment)
      /* if not marked as continuing, assume this is the final fragment */
      firstbyte |= WSBIT_FIN | opcode;
    else
      /* if marked as continuing, assume this is the final fragment; keep a CONT opcode and set FIN bit */
      firstbyte |= WSBIT_FIN | WSBIT_OPCODE_CONT;
    ws->ws.contfragment = FALSE;
  }
  else if(ws->ws.contfragment) {
    /* the previous fragment was not a final one and this isn't either, keep a
       CONT opcode and no FIN bit */
    firstbyte |= WSBIT_OPCODE_CONT;
  }
  else {
      firstbyte = opcode;   // first frame: preserve opcode
      ws->ws.contfragment = TRUE;
  }

I am sending multi frames in this way:

send(frame1, CURLWS_BINARY | CURLWS_CONT) // sending as BINARY with FIN==0
send(frame2, CURLWS_BINARY | CURLWS_CONT) // sending as CONT with FIN==0
send(frame2, CURLWS_BINARY | CURLWS_CONT) // sending as CONT with FIN==0
...
send(lastframe, CURLWS_BINARY) // sending as CONT with FIN==1

[bagder]

Thanks for the patch @mikeduglas! Can you turn that into a proper PR or would you prefer I do it?

[mikeduglas]

@bagder Please do it yourself, I can't.