Websocket transport with native websockets

[sphaero]

Libzmq has (DRAFT) websocket transport support since quite some time. However this requires the jszmq js library. It would be great to support native websockets as well which currently does not work.

I haven't found the path in the code yet where it happens but websocket requests not talking ZWS are immediately dropped I guess.

Perhaps using a STREAM socket it should be easy to support native websockets. For example using the browser without the jszmq lib.

Has anyone worked on this? Any suggestions what should/could be done?

[somdoron]

You can use it directly from the browser, without jszmq, it should work. Two things you need to know is that zeromq only sends binary messages on the websocket, plus the first byte is the more flag. You can learn more how to use it here: https://github.com/zeromq/jszmq/blob/master/src/webSocketEndpoint.ts

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On Tue, Apr 1, 2025 at 1:39 PM Arnaud Loonstra ***@***.***> wrote: Libzmq has (DRAFT) websocket transport support since quite some time. However this requires the jszmq js library. It would be great to support native websockets as well which currently does not work. I haven't found the path in the code yet where it happens but websocket requests not talking ZWS are immediately dropped I guess. Perhaps using a STREAM socket it should be easy to support native websockets. For example using the browser without the jszmq lib. Has anyone worked on this? Any suggestions what should/could be done? — Reply to this email directly, view it on GitHub <#4781>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAUW75XWHRDM6PHN3FLJY4D2XJUHVAVCNFSM6AAAAAB2GRIDGSVHI2DSMVQWIX3LMV43ASLTON2WKOZSHE3DGMBTGU2TAMQ> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***> [image: sphaero]*sphaero* created an issue (zeromq/libzmq#4781) <#4781> Libzmq has (DRAFT) websocket transport support since quite some time. However this requires the jszmq js library. It would be great to support native websockets as well which currently does not work. I haven't found the path in the code yet where it happens but websocket requests not talking ZWS are immediately dropped I guess. Perhaps using a STREAM socket it should be easy to support native websockets. For example using the browser without the jszmq lib. Has anyone worked on this? Any suggestions what should/could be done? — Reply to this email directly, view it on GitHub <#4781>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAUW75XWHRDM6PHN3FLJY4D2XJUHVAVCNFSM6AAAAAB2GRIDGSVHI2DSMVQWIX3LMV43ASLTON2WKOZSHE3DGMBTGU2TAMQ> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[somdoron]

Actually, the protocol is also documented here:

https://rfc.zeromq.org/spec/45/

[sphaero]

Thanks for the pointers Doron. I've managed to use minimal browser code to connect to a 0mq socket. It's very rudimentary code so not well tested but at least it gets a message across. Using a PULL socket on the other side. Code at the bottom for reference.

Still I'd like to be able to connect a plain Websocket like we can do with a STREAM socket and a plain TCP socket. Sometimes I run into existing softwate that can only connect to a Websocket endpoint but I have no (or limited) control over what messages it sends. I'll look further into the libzmq implementation.

const socket = new WebSocket('ws://127.0.0.1:9000', ['ZWS2.0']);
socket.binaryType = "arraybuffer";

socket.onopen = () => {
  console.log('WebSocket connection established.');
  msg = createZwsMessage([
    "client-identity" // Frame 1 (ZMQ_SNDMORE)
  ]);
  socket.send(msg);
  

  msg = createZwsMessage([
    "Hello, ZeroMQ!"   // Frame 2 (final)
  ]);
  socket.send(msg);
};

socket.onmessage = (event) => {
  const receivedData = new Uint8Array(event.data);
  console.log(receivedData.toString());
  const more = receivedData[0] === 1;
  const msg = receivedData.slice(1);
  if (msg.length)
  {
      const receivedMessage = new TextDecoder().decode(msg);
      console.log('Received message:', receivedMessage);
  }
};

socket.onerror = (error) => {
  console.error('WebSocket error:', error);
};

socket.onclose = () => {
  console.log('WebSocket connection closed.');
};

function createZwsMessage(frames) {
  const encoder = new TextEncoder();
  const parts = [];

  frames.forEach((str, index) => {
    const data = encoder.encode(str);
    const hasMore = index < frames.length - 1;
    const flags = hasMore ? 0x01 : 0x00;  // ZWS_MORE flag

    const frame = new Uint8Array(1 + data.length);
    frame[0] = flags;
    frame.set(data, 1);

    parts.push(frame);
  });

  // Combine all parts into one ArrayBuffer
  const totalLength = parts.reduce((sum, part) => sum + part.length, 0);
  const message = new Uint8Array(totalLength);
  let offset = 0;
  for (const part of parts) {
    message.set(part, offset);
    offset += part.length;
  }

  return message.buffer; // Return as ArrayBuffer
}