fetch-h2

Fetch API implementation for Node.js using the built-in http, https and http2 packages without any compatibility layer.

fetch-h2 handles HTTP/1(.1) and HTTP/2 connections transparently since 2.0. By default (although configurable) a url to http:// uses HTTP/1(.1) and for the very uncommon plain-text HTTP/2 (called h2c), http2:// can be provided. The library supports ALPN negotation, so https:// will use either HTTP/1(.1) or HTTP/2 depending on what the server supports. By default, HTTP/2 is preferred.

The library handles sessions transparently and re-uses sockets when possible.

fetch-h2 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 br, gzip and deflate encodings, and decodes transparently.

Releases

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

Since 2.0.0, fetch-h2 requires Node.js 10.4.

Since 2.4.0, fetch-h2 has full TLS SAN (Subject Alternative Name) support.

Since 3.0.0, fetch-h2 requires Node.js 12.

API

Imports

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,
    AbortController,
    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) and the AbortController provides a way to abort requests.

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 a 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 for the cloned Request.
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.
The Request class (options to fetch) has an extra property allowForbiddenHeaders, which defaults to false.
The Response class also has an extra property allowForbiddenHeaders, which defaults to false (or to the value of the Request if it was constructed through a fetch call, which is the common case).
The response object has an extra property httpVersion which is either 1 or 2 (numbers), depending on what was negotiated with the server.
The Headers class (e.g. retried by {response}.headers) has a toJSON function which converts the headers to a simple JavaScript object.

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 |
        PerOrigin< string >;
    overwriteUserAgent:
        boolean |
        PerOrigin< boolean >;
    accept:
        string |
        PerOrigin< string >;
    cookieJar:
        CookieJar;
    decoders:
        ReadonlyArray< Decoder > |
        PerOrigin< ReadonlyArray< Decoder > >;
    session:
        SecureClientSessionOptions |
        PerOrigin< SecureClientSessionOptions >;
    httpProtocol:
        HttpProtocols |
        PerOrigin< HttpProtocols >;
    httpsProtocols:
        ReadonlyArray< HttpProtocols > |
        PerOrigin< ReadonlyArray< HttpProtocols > >;
    http1:
        Partial< Http1Options > |
        PerOrigin< Partial< Http1Options > >;
}

where Http1Options is

interface Http1Options
{
	keepAlive: boolean | PerOrigin< boolean >;
	keepAliveMsecs: number | PerOrigin< number >;
	maxSockets: number | PerOrigin< number >;
	maxFreeSockets: number | PerOrigin< number >;
	timeout: void | number | PerOrigin< void | number >;
}

Per-origin configuration

Any of these options, except for the cookie jar, can be provided either as a value or as a callback function (PerOrigin) which takes the origin as argument and returns the value. A void return from that function, will use the built-in default.

User agent

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

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

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

Cookies

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.

Content encodings (compression)

By default, gzip and deflate are supported, and br (Brotli) if running on Node.js 11.7+.

decoders can be an array of custom decoders, such as fetch-h2-br which adds Brotli content decoding support for older versions of node (< 11.7).

Low-level session configuration

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.

Some of these fields are compatible with HTTP/1.1 too, such as rejectUnauthorized.

HTTP Protocols

The type HttpProtocols is "http1" | "http2".

The option httpProtocol can be set to either "http2" or "http1" (the default). This controls what links to http:// will use. Note that no web server will likely support HTTP/2 unencrypted.

httpsProtocol is an array of supported protocols to negotiate over https. It defaults to [ "http2", "http1" ], but can be swapped to prefer HTTP/1(.1) rather than HTTP/2, or to require one of them by only containing that protocol.

HTTP/1

HTTP/2 allows for multiple concurrent streams (requests) over the same session (socket). HTTP/1 has no such feature, so commonly, clients open a set of connections and re-use them to allow for concurrency.

The http1 options object can be used to configure this.

Keep-alive

http1.keepAlive defaults to true, to allow connections to linger so that they can be reused. The http1.keepAliveMsecs time (defaults to 1000ms, i.e. 1s) specifies the delay before keep-alive probing.

Sockets

http1.maxSockets defines the maximum sockets to allow per origin, and http1.maxFreeSockets the maximum number of lingering sockets, waiting to be re-used for new requests.

http1.timeout defines the HTTP/1 timeout.

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 } );

grantila/fetch-h2

grantila

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