fetch-h2

What is fetch-h2?

The fetch-h2 npm package is a modern HTTP/2 client for Node.js, providing a fetch API compatible interface. It allows you to make HTTP/2 requests with ease, leveraging the benefits of HTTP/2 such as multiplexing, header compression, and server push.

What are fetch-h2's main functionalities?

Basic HTTP/2 GET Request

This feature allows you to make a basic HTTP/2 GET request to a specified URL and log the response body.

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

(async () => {
  const response = await fetch('https://example.com');
  const body = await response.text();
  console.log(body);
})();

HTTP/2 POST Request with JSON Body

This feature allows you to make an HTTP/2 POST request with a JSON body to a specified URL and log the JSON response.

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

(async () => {
  const response = await fetch('https://example.com/api', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ key: 'value' })
  });
  const json = await response.json();
  console.log(json);
})();

Handling HTTP/2 Server Push

This feature demonstrates how to handle server push in HTTP/2, where the server can send additional resources to the client without the client explicitly requesting them.

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

(async () => {
  const response = await fetch('https://example.com');
  response.on('push', (pushStream) => {
    pushStream.on('data', (chunk) => {
      console.log('Pushed data:', chunk.toString());
    });
  });
})();

Other packages similar to fetch-h2

http2

The http2 package is a core Node.js module that provides an implementation of the HTTP/2 protocol. It offers lower-level control over HTTP/2 connections compared to fetch-h2, which provides a higher-level, fetch-like API.

axios

Axios is a popular HTTP client for Node.js and the browser. While it primarily supports HTTP/1.1, it can be used with HTTP/2 by configuring it with an HTTP/2-compatible adapter. Axios provides a promise-based API similar to fetch-h2 but is more widely used and has a larger community.

node-fetch

Node-fetch is a lightweight module that brings the window.fetch API to Node.js. It supports HTTP/1.1 and can be extended to support HTTP/2 with additional configuration. Node-fetch is similar to fetch-h2 in providing a fetch-like API but does not natively support HTTP/2.

README

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.

By default, fetch-h2 will accept gzip and deflate encodings, and decode transparently. If you also want to allow Brotli (br), use the fetch-h2-br package.

NOTE; HTTP/2 support was 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. The API has changed and not settled until 10.x, and fetch-h2 requires 10.x.

Releases

Since 1.0.0, fetch-h2 requires Node.js 10.

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

    ContextOptions,
    DecodeFunction,
    Decoder,

    CookieJar,

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

Apart from the obvious fetch, the functions setup, 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 ContextOptions, DecodeFunction and Decoder types are described below.

The CookieJar class can be used to control cookie handling (e.g. to read the cookies manually).

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...
    }
} );

To unset the push handler (and ignore future pushes) when it has been set to a function previously, call onPush without any arguments.

import { onPush } from 'fetch-h2'

onPush( push_fun );
// ... later
onPush( ); // Reset push handling to ignore pushes from now

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 and validates unless 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.
• The response text() and arrayBuffer() has an optional argument allowIncomplete which defaults to false. If set to true these function will return incomplete bodies, i.e. "as much as was read" before the stream was prematurely closed (disconnected). If integrity checks are enabled, the functions will throw anyway if the body is incomplete.

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( );

Contexts can be configured with options when constructed. The default context can be configured using the setup( ) function, but if this function is used, call it only once, and before any usage of fetch-h2, or the result is undefined.

Context configuration

The options to setup( ) are the same as those to context( ) and is available as a TypeScript type ContextOptions.

// The options object
interface ContextOptions
{
    userAgent: string;
    overwriteUserAgent: boolean;
    accept: string;
    cookieJar: CookieJar;
    decoders: ReadonlyArray< Decoder >;
    session: SecureClientSessionOptions;
}

By specifying a userAgent string, this will be added to the built-in user-agent header. If defined, and overwriteUserAgent is true, the built-in user agent string will not be sent.

accept can be specified, which is the accept header. The default is:

application/json, text/*;0.9, */*;q=0.8

cookieJar can be set to a custom cookie jar, constructed as new CookieJar( ). CookieJar is a class exported by fetch-h2 and has three functions:

{
    setCookie( cookie: string | Cookie, url: string ): Promise< Cookie >;
    setCookies( cookies: ReadonlyArray< string | Cookie >, url: string ): Promise< Cookie >;
    getCookies( url: string ): Promise< ReadonlyArray< Cookie > >;
    reset( ); // Clears all cookies
}

where Cookie is a tough-cookie Cookie.

decoders can be an array of custom decoders, such as fetch-h2-br which adds Brotli content decoding support.

session can be used for lower-level Node.js settings. This is the options to http2::connect (including the net::connect and tls::connect options). Use this option to specify {rejectUnauthorized: false} if you want to allow unauthorized (e.g. self-signed) certificates.

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 } );