fastify-sse

Easily send Server-Send-Events with Fastify.

This is based on github.com/mtharrison/susie

Install

npm install --save fastify-sse

Usage

Add it to you project with register and you are done!

You can now configure a new route, and call the new reply.sse() to send Events to browser.

When you have finished sending event, you could send an empty message, or if using stream and end of stream, an end event will be fired just before closing the connection. You could work with it browser side to prevent automatic reconnection.

// Register the plugin
fastify.register(require("fastify-sse"), (err) => {
    if (err) {
      throw err;
    }
});

// Define a new route in hapijs notation
fastify.route({
  method: "GET",
  url: "/sse-hapi",
  handler: (request, reply) => {
    let index;
    const options = {};

    // Send the first data
    reply.sse("sample data", options);
    
    // Send a new data every seconds for 10 seconds then close
    const interval = setInterval(() => {
      reply.sse({event: "test", data: index});
      if (!(index % 10)) {
        reply.sse();
        clearInterval(interval);
      }
    }, 1000);
  }
});

// Define a new route in express notation
fastify.get("/sse-express",(request, reply) => {
    let index;
    const options = {};

    // Send the first data
    reply.sse("sample data", options);
    
    // Send a new data every seconds for 10 seconds then close
    const interval = setInterval(() => {
      reply.sse({event: "test", data: index});
      if (!(index % 10)) {
        reply.sse();
        clearInterval(interval);
      }
    }, 1000);
  });

The options are used only for the first call, subsequent ignore it.

You could specify:

• strings that well be sent directly
• buffers that will be converted beck to strings, utf8 encoded
• objects that will be stringified with the use of "fast-safe-stringify"
• streams that are readables, and could deals with objectMode or not

Options

• idGenerator: generate the event id, defaulting to a number incrementing, from 1
• event: can be a string for the event name, or a function to compute the event name

idGenerator

It must be a function that will be called with the event in parameter, and must return a string that will be the id of the SSE, or it could be null if no id is needed.

Using a function:

reply.sse("message", {
  idGenerator: (event) => {
    // Retrieve the event name using the key myIdentifiant or use the timestamp if not exists …
    return event.myIdentifiant || (new Date()).getTime();
  }
});

It will transmit:

id: 1504624133267

data: message

Do not display id, so pass null:

reply.sse("message", {idGenerator: null});

It will transmit:

data: message

event

It could be:

• a function, called with the event in parameter and return a string that will be used, or a string if the event name doest not change. The event will be retrieved by the browser using .on("eventName", […]).
• nothing if you do not want a name, and events could be retrieved in the browser with the generic .on("message", […]).

reply.sse({myEventName: "myEvent", hello: "world"}, {
  event: (event) => {
    // Retrieve the event name using the key myEventName …
    const name = event.myEventName;
    // … delete it from the object …
    delete event.myEventName;
    // then return the name
    return name;
  }
});

It will transmit:

id: 1

event: MyEvent

data: {"hello":"world"}