send() return value of 0

[KrishnaPG]

The documentation of send method indicates:

Returns 1 for success, 2 for dropped due to backpressure limit, and 0 for built up backpressure that will drain over time.

When the return value is 0:

• does it mean the message has been added to the socket buffer queue (and will be sent soon), or should we call send again with the same message after the drain event?

I would like to retry the failed messages. Is this below approach correct? I am maintaining a retryQ[] to keep track of failed messages so that I can retry them after the drain event. It is not clear how to handle the return value 0.

const retryQ= [];

const sendNow = (ws, msg) => {
  const status = ws.send(msg, true, true);
  switch (status) {
    case 1:  // sent successfully, nothing to do
      return status;
    case 2: { // dropped due to backpressure, lets try again later after drain even
      retryQ.push(msg);
      return status;
    }
    case 0: { // built-up backpressure: what should be done????
      retryQ.push(msg);  //<<-- should we retry the message again or has it already been queued at socket?
      return status;
    }
  }
};

[e3dio]

 case 0: { // built-up backpressure: what should be done????

It is already in backpressure queue ready to send out, you don't need to do anything there. Only need to handle the dropped messages

[KrishnaPG]

Thank you @e3dio

[KrishnaPG]

One follow-up question on this case 0 (message in the backpressure queue) :

• how does the socket process the messages that are put in the backpressure queue, since Node.js is single-threaded? Are there threads in the C++ side that take care of these backpressure queued ones, or should something be done from the Node.js side to let the socket process them?

[uNetworkingAB]

it's the same as any other nodejs project. you do nothing special