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express-stream

Response streaming middleware for Express 4.

IMPORTANT: If you want your streamed responses to have GZIP enabled, please use the excellent express compression middleware. If you use compression as an app-wide middleware, express-stream will automatically take advantage of it.

Check out the demo app.

What is This?

express-stream exposes two middleware functions.

  • stream.pipe() is the least opinionated BigPipe implementation around and is ideal for client-side rendering
  • stream.stream() is ideal for server-side rendering

Both methods allow you to get content in front of your users as fast as possible by taking forms of latency that generally occur sequentially and making them occur in parallel.

Basic Client-Side Render/BigPipe Usage

//Requires
var express = require('express');
var ejs = require('ejs');
var stream = require('express-stream');
var superagent = require('superagent');

//App setup
var app = express();
app.set('views', './views');
app.set('view engine', 'ejs');

//Add the middleware to the desired routes
app.get('/', stream.pipe(), function (req, res) {
  res.stream('landing'); //Stream the landing page
  superagent
    .get(uri)
    .end(function (err, response){
      res.stream('landing-data', {response.body.data}); //Stream data to populate the landing page
      res.close();
    }
  );
});

This example would immediately stream 'landing' to the browser while the superagent call fetches the dynamic parts of the page. As soon as the superagent call resolves, it is streamed within a self-executing JavaScript block from which it injects some data into the already-rendered view.

Basic Server-Side Render Usage

//Requires
var express = require('express');
var ejs = require('ejs');
var stream = require('express-stream');

//App setup
var app = express();
app.set('views', './views');
app.set('view engine', 'ejs');

//App-wide streaming setup
stream.useAllAutoTags(true);
stream.streamBefore('pre-body-view');
stream.streamAfter('post-body-view');

//Add the middleware to the desired routes
app.get('/', stream.stream(), function (req, res) {
  res.stream('landing'); //This route will now stream
  res.close();
});

This example streams the pre-body-layout view as soon as the stream.stream() middleware is run, and then landing and post-body-layout as soon as res.render() is called.

API

A note about the API section

Because express-stream's two middleware functions patch express's res object differently, the API section is divided into two portions--one for each middleware function. Any functions you see within a section are only applicable when used with the middleware from the same portion of the API. stream.pipe()'s API is simpler so it's in a table. stream.stream()'s API is more complex so it's written out with examples.

stream.pipe()

Function Scope Description Arguments
stream.pipe() middleware This middleware function is written for client-side rendering. It can be used as a loose BigPipe implementation. N/A
res.stream(view, options) res When you use .pipe(), this funciton is added to the res object. It is the same as res.render() except that it does not close the HTTP connection and does not accept a callback Same as express
res.streamText(output) res Send a string of text to the client Output: Text output as a string
res.close() res Closes the connection when finished.

stream.stream()

.globalOptions(options)

App-wide API Call

Set an app-wide options object to be merged with the options param passed to all res.render() and res.stream() calls.

Arguments

  • options: type: object, default: {}

.streamBefore(view, options)

App-wide API Call

Set an app-wide view, or array of views, to stream as soon as the stream.stream() middleware is run. It's recommended that the views passed to .streamBefore() be used to open the <html> and <head> tags and list site-wide dependencies.

If view is an array, all other passed params will be ignored.

Arguments

  • view: type: string || array of strings || array of objects
  • options: same as express's options param

Examples

With view as a string

stream.streamBefore('global-head', {custom: data});

With view as an array of strings

stream.streamBefore(['global-head-one', 'global-head-two']);

With view as an array of objects

var globalHeadList = [
  {view: 'global-head-one', options: {custom: data}},
  {view: 'global-head-two'}
]
stream.streamBefore(globalHeadList);

.streamAfter(view, options)

App-wide API Call

Set an app-wide view, or array of views, to stream as soon as the res.render() call completes. It's recommended that the views passed to .streamAfter() be used to close the <body> and <html> tags.

If view is an array, all other passed params will be ignored.

Arguments

  • view: type: string || array of strings || array of objects
  • options: same as express's options param

Examples

With view as a string

stream.streamAfter('global-footer', {custom: data});

With view as an array of strings

stream.streamAfter(['global-footer-one', 'global-footer-two']);

With view as an array of objects

var globalHeadList = [
  {view: 'global-footer-one', options: {custom: data}},
  {view: 'global-footer-two'}
]
stream.streamAfter(globalHeadList);

.openHtmlOpenHead(view, options)

App-wide API Call

If view is true, this will simply stream a <!doctype html><html><head> string to the client. If view is a string, this will stream the associated view with optional options.

Arguments

  • view: boolean or string
  • options: same as express's options param

.closeHeadOpenBody(view, options)

App-wide API Call

If view is true, this will simply stream a </head><body> string to the client. If view is a string, this will stream the associated view with optional options.

Arguments

  • view: boolean or string
  • options: same as express's options param

.closeBodyCloseHtml(view, options)

App-wide API Call

If view is true, this will simply stream a </body></html> string to the client. If view is a string, this will stream the associated view with optional options.

Arguments

  • view: boolean or string
  • options: same as express's options param

.useAllAutoTags(val)

App-wide API Call

A convenience method to set the same boolean value for openHtmlOpenHead, closeHeadOpenBody, and closeBodyCloseHtml in a single call.

Arguments

  • val: boolean or string

.stream(headView, headOptions)

Middleware-only API Call

Set an optional route-specific view, or list of views, to be rendered after the .streamBefore() array and before any res.stream()/res.render() views. It's recommended that your .streamBefore() views not close the <head> tag so that route-specific blocking dependencies can be injected into the <head> here.

If headView is an array, all other passed params will be ignored.

Arguments

  • headView: type: string || array of strings || array of objects
  • headOptions: same as express's options param

Examples

With headView as a string

app.get('/stream-route', stream.stream('render-blocking-assets', {custom: data}), function (req, res){
  res.stream('stream-body');
  res.close();
});

With headView as an array of strings

app.get('/stream-route', stream.stream(['blocking-one', 'blocking-two']), function (req, res){
  res.stream('stream-body');
  res.close();
});

With headView as an array of objects

var blockingList = [
  {view: 'blocking-one', options: {custom: data}},
  {view: 'blocking-two'}
]
app.get('/stream-route', stream.stream(blockingList), function (req, res){
  res.stream('stream-body');
  res.close();
});

res.stream(view, options)

Route-specific API Call

Compiles and streams a view just like res.render(), but does not trigger the .streamAfter() array and does not close the connection.

Arguments

  • All arguments are identical to express's res.render() call expect that callback is missing.

res.streamText(text)

Route-specific API Call

Streams the provided text to the client.

Arguments

  • All arguments are identical to express's res.render() call excpet that callback is missing.

More!

Usage examples are coming. In the mean time, see this demo app.

Breaking Change History

1.0.0

  • stream.pipe() now only exposes res.stream(view, data), res.streamText(text), and res.close().
  • stream.stream()'s res.render(view, data) function is now res.stream(view, data).
  • Custom res.* functions no longer accept the callback param.