README.md

fetch-h2

HTTP/2 Fetch API implementation for Node.js (using Node.js' built-in http2 module). This module is intended to be solely for HTTP/2, handling HTTP/2 sessions transparently. For an HTTP/1(.1)-only alternative, you can use node-fetch.

The module tries to adhere to the Fetch API very closely, but extends it slightly to fit better into Node.js (e.g. using streams).

Regardless of whether you're actually interested in the Fetch API per se or not, as long as you want to handle HTTP/2 client requests in Node.js, this module is a lot easier and more natural to use than the native built-in http2 module which is low-level in comparison.

fetch-h2 supports cookies (per-context, see below), so when the server sends 'set-cookie' headers, they are saved and automatically re-sent, even after disconnect. They are however only persisted in-memory.

NOTE; HTTP/2 support was recently introduced in Node.js (version 8.4), and required node to be started with a flag --expose-http2 up to version 8.7 (this module won't work without it). From Node.js 8.8, the http2 module is available without any flag.

DISCLAIMER: This is an early project, don't expect everything to "just work".

Imports

This README uses the ES6/TypeScript import syntax, mainly because fetch-h2 is written in TypeScript (and also because ES6 modules will eventually arrive in Node.js). If you use pure JavaScript in Node.js today, you don't have modules support, just require instead, e.g:

const { fetch } = require( 'fetch-h2' );

fetch-h2 exports more than just fetch(), namely all necessary classes and functions for taking advantage of the Fetch API (and more).

import {
    context,
    fetch,
    disconnect,
    disconnectAll,
    onPush,
    Body,
    Headers,
    Request,
    Response,
    AbortError,
    TimeoutError,

    // TypeScript types:
    OnTrailers,
} from 'fetch-h2'

Apart from the obvious fetch, the functions context, disconnect, disconnectAll and onPush are described below, and the classes Body, Headers, Request and Response are part of the Fetch API. AbortError is the error thrown in case of an abort signal (this is also the error thrown in case of a timeout, which in fetch-h2 is internally implemented as an abort signal), TimeoutError is thrown if the request times out.

The OnTrailers is the type for the onTrailers callback.

Usage

Import fetch from fetch-h2 and use it like you would use fetch in the browser.

import { fetch } from 'fetch-h2'

const response = await fetch( url );
const responseText = await response.text( );

With HTTP/2, all requests to the same origin (domain name and port) share a single session (socket). In browsers, it is eventually disconnected, maybe. It's up to the implementation to handle disconnections. In fetch-h2, you can disconnect it manually, which is great e.g. when using fetch-h2 in unit tests.

Disconnect

Disconnect the session for a certain url (the session for the origin will be disconnected) using disconnect, and disconnect all sessions with disconnectAll. Read more on contexts below to understand what "all" really means...

import { disconnect, disconnectAll } from 'fetch-h2'

await disconnect( "http://mysite.com/foo" ); // "/foo" is ignored, but allowed
// or
await disconnectAll( );

Pushed requests

When the server pushes a request, this can be handled using the onPush handler. Registering an onPush handler is, just like the disconnection functions, per-context.

import { onPush } from 'fetch-h2'

onPush( async ( origin, request, getResponse ) =>
{
    if ( shouldReceivePush( request ) )
    {
        const response = await getResponse( );
        // do something with response...
    }
} );

Limitations

fetch-h2 has a few limitations, some purely technical, some more fundamental or perhaps philosophical, which you will find in the Fetch API but missing here.

• There is no automatic CORS handling, since you don't have the concept of web pages with cross-origin resource sharing. You have full control over your code, at least that's what fetch-h2 believes.
• The Body class/mixin doesn't support the formData() function. This can be added if someone really wants it - PR's are welcome.
• The Body class/mixin doesn't support the blob() function. This type of buffer doesn't exist in Node.js, use arrayBuffer() instead.
• Automatic redirection (3xx codes) are only supported for HEAD and GET requests. If e.g. a POST request gets a 3xx-code response and redirect is set to follow, the result is an error. Redirections for non-idempotent requests are only allowed if redirect is error or manual (which is the default). Note that the default for redirect is different among browsers (and even versions of them). The specs are non-obvious but seems to suggest manual initially, followed by follow. It's a good idea to explicitly set redirect and not depend on any default.
• The credentials option is currently not used. Cookies are always sent to the same origin, and not to others.
• The cache option is unused, as fetch-h2 has no built-in cache.
• The referrer and referrerPolicy are unused, as fetch-h2 operates outside the concept of "web pages".
• The integrity option is actually implemented but no validation is performed if the result body is read through the Node.js ReadableStream (using response.readable( )). The body is validated if arrayBuffer( ), json( ) or text( ) is used to read the body, in which case these functions will return a rejected promise if the validation fails.

Extensions

These are features in fetch-h2, that don't exist in the Fetch API. Some things are just very useful in a Node.js environment (like streams), some are due to the lack of a browser with all its responsibilities.

• When redirect is set to manual, the response is supposed to be empty and useless, with no status code or anything (according to spec). In fetch-h2, it's a normal useful Response object.
• The body that can be sent in a Request, and that is available on the Response, can be a Node.js ReadableStream. You can thereby stream data with a request, and stream the response body.
• The body that can be sent in a Request can be a Body object. It can also be a string or buffer.
• fetch() has an extra option, json that can be used instead of body to send an object that will be JSON stringified. The appropriate content-type will be set if it isn't already.
• fetch() has an extra option, timeout which is a timeout in milliseconds before the request should be aborted and the returned promise thereby rejected (with an TimeoutError).
• fetch() has an extra option, onTrailers (of the type OnTrailers) which is a callback that will receive trailing headers.
• The Request.clone() member function has an optional url argument.

Contexts

HTTP/2 expects a client implementation to not create new sockets (sessions) for every request, but instead re-use them - create new requests in the same session. This is also totally transparent in the Fetch API. It might be useful to control this, and create new "browser contexts", each with their own set of HTTP/2-sessions-per-origin. This is done through the context function.

This function returns an object which looks like the global fetch-h2 API, i.e. it will have the functions fetch, disconnect and disconnectAll.

import { context } from 'fetch-h2'

const ctx = context( /* options */ );

ctx.fetch( url | Request, init?: InitOpts );
ctx.disconnect( url );
ctx.disconnectAll( );
ctx.onPush( ... );

The global fetch, disconnect, disconnectAll and onPush functions are default-created from a context internally. They will therefore not interfere, and disconnect/disconnectAll/onPush only applies to its own context, be it a context created by you, or the default one from fetch-h2.

If you want one specific context in a file, why not destructure the return in one go?

import { context } from 'fetch-h2'
const { fetch, disconnect, disconnectAll, onPush } = context( );

Errors

When an error is thrown (or a promise is rejected), fetch-h2 will always provide proper error objects, i.e. instances of Error.

Circular redirection

If servers are redirecting a fetch operation in a way that causes a circular redirection, e.g. servers redirect A -> B -> C -> D -> B, fetch-h2 will detect this and fail the operation with an error. The error object will have a property urls which is an array of the urls that caused the loop (in this example it would be [ B, C, D ], as D would redirect to the head of this list again).

More examples

Fetch JSON

Using await and the Body.json() function we can easily get a JSON object from a response.

import { fetch } from 'fetch-h2'

const jsonData = await ( await fetch( url ) ).json( );

Post JSON

Use the json property instead of body to send an application/json body. This is an extension in fetch-h2, not existing in the Fetch API.

import { fetch } from 'fetch-h2'

const method = 'POST';
const json = { foo: 'bar' };
const response = await fetch( url, { method, json } );

Post anything

Similarly to posting JSON, posting a buffer, string or readable stream can be done through the body property.

import * as fs from 'fs'
import { fetch } from 'fetch-h2'

const method = 'POST';

const body = "some data";
const response = await fetch( url, { method, body } );

// or

const body = fs.readFileSync( 'my-file' );
const response = await fetch( url, { method, body } );

// or

const body = fs.createReadStream( 'my-file' );
const response = await fetch( url, { method, body } );