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    6.0.1 • Public • Published


    CI NPM version Known Vulnerabilities Coverage Status js-standard-style

    Fastify plugin to forward the current HTTP request to another server. HTTP2 to HTTP is supported too.


    npm i fastify-reply-from

    Compatibility with fastify-multipart

    fastify-reply-from and fastify-multipart should not be registered as sibling plugins nor should they be registered in plugins which have a parent-child relationship.
    The two plugins are incompatible, in the sense that the behavior of fastify-reply-from might not be the expected one when the above-mentioned conditions are not respected.
    This is due to the fact that fastify-multipart consumes the multipart content by parsing it, hence this content is not forwarded to the target service by fastify-reply-from.
    However, the two plugins may be used within the same fastify instance, at the condition that they belong to disjoint branches of the fastify plugins hierarchy tree.


    The following example set up two Fastify servers and forward the request from one to the other:

    'use strict'
    const Fastify = require('fastify')
    const target = Fastify({
      logger: true
    target.get('/', (request, reply) => {
      reply.send('hello world')
    const proxy = Fastify({
      logger: true
    proxy.register(require('fastify-reply-from'), {
      base: 'http://localhost:3001/'
    proxy.get('/', (request, reply) => {
    target.listen(3001, (err) => {
      if (err) {
        throw err
      proxy.listen(3000, (err) => {
        if (err) {
          throw err


    Plugin options


    Set the base URL for all the forwarded requests. Will be required if http2 is set to true Note that every path will be discarded.

    Custom URL protocols unix+http: and unix+https: can be used to forward requests to a unix socket server by using querystring.escape(socketPath) as the hostname. This is not supported for http2 nor undici. To illustrate:

    const socketPath = require('querystring').escape('/run/http-daemon.socket')
    proxy.register(require('fastify-reply-from'), {
      base: 'unix+http://${socketPath}/'


    By default, undici will be used to perform the HTTP/1.1 requests. Enabling this flag should guarantee 20-50% more throughput.

    This flag could controls the settings of the undici client, like so:

    proxy.register(require('fastify-reply-from'), {
      base: 'http://localhost:3001/',
      // default settings
      undici: {
        connections: 128,
        pipelining: 1,
        keepAliveTimeout: 60 * 1000,
        tls: {
          rejectUnauthorized: false

    See undici own options for more configurations.


    Set the http option to true or to an Object to use Node's http.request will be used if you do not enable http2. To customize the request, you can pass in agentOptions and requestOptions. To illustrate:

    proxy.register(require('fastify-reply-from'), {
      base: 'http://localhost:3001/',
      http: {
        agentOptions: { // pass in any options from
          keepAliveMsecs: 10 * 60 * 1000
        requestOptions: { // pass in any options from
          timeout: 5000 // timeout in msecs, defaults to 10000 (10 seconds)

    You can also pass custom HTTP agents. If you pass the agents, then the http.agentOptions will be ignored. To illustrate:

    proxy.register(require('fastify-reply-from'), {
      base: 'http://localhost:3001/',
      http: {
        agents: {
          'http:': new http.Agent({ keepAliveMsecs: 10 * 60 * 1000 }), // pass in any options from
          'https:': new https.Agent({ keepAliveMsecs: 10 * 60 * 1000 })
        requestOptions: { // pass in any options from
          timeout: 5000 // timeout in msecs, defaults to 10000 (10 seconds)


    You can either set http2 to true or set the settings object to connect to a HTTP/2 server. The http2 settings object has the shape of:

    proxy.register(require('fastify-reply-from'), {
      base: 'http://localhost:3001/',
      http2: {
        sessionTimeout: 10000, // HTTP/2 session timeout in msecs, defaults to 60000 (1 minute)
        requestTimeout: 5000, // HTTP/2 request timeout in msecs, defaults to 10000 (10 seconds)
        sessionOptions: { // HTTP/2 session connect options, pass in any options from
          rejectUnauthorized: true
        requestTimeout: { // HTTP/2 request options, pass in any options from
          endStream: true


    The number of parsed URLs that will be cached. Default: 100.


    This option will disable the URL caching. This cache is dedicated to reduce the amount of URL object generation. Generating URLs is a main bottleneck of this module, please disable this cache with caution.


    An array of content types whose response body will be passed through JSON.stringify(). This only applies when a custom body is not passed in. Defaults to:



    On which methods should the connection be retried in case of socket hang up.
    Be aware that setting here not idempotent method may lead to unexpected results on target.

    By default: ['GET', 'HEAD', 'OPTIONS', 'TRACE' ]

    reply.from(source, [opts])

    The plugin decorates the Reply instance with a from method, which will reply to the original request from the desired source. The options allows to override any part of the request or response being sent or received to/from the source.

    Note: If base is specified in plugin options, the source here should not override the host/origin.

    onResponse(request, reply, res)

    Called when a HTTP response is received from the source. The default behavior is reply.send(res), which will be disabled if the option is specified.

    When replying with a body of a different length it is necessary to remove the content-length header.

      onResponse: (request, reply, res) => {
        reply.send('New body of different length');

    onError(reply, error)

    Called when a HTTP response is received with error from the source. The default behavior is reply.send(error), which will be disabled if the option is specified. It must reply the error.


    Called to rewrite the headers of the response, before them being copied over to the outer response. It must return the new headers object.

    rewriteRequestHeaders(originalReq, headers)

    Called to rewrite the headers of the request, before them being sent to the other server. It must return the new headers object.

    getUpstream(originalReq, base)

    Called to get upstream destination, before the request is being sent. Useful when you want to decide which target server to call based on the request data. Helpful for a gradual rollout of new services. It must return the upstream destination.


    Replaces the original querystring of the request with what is specified. This will be passed to querystring.stringify.


    Replaces the original request body with what is specified. Unless contentType is specified, the content will be passed through JSON.stringify(). Setting this option for GET, HEAD requests will throw an error "Rewriting the body when doing a {GET|HEAD} is not allowed".


    How many times it will try to pick another connection on socket hangup (ECONNRESET error).
    Useful when keeping the connection open (KeepAlive).
    This number should be a function of the number of connections and the number of instances of a target.

    By default: 0 (disabled)


    Override the 'Content-Type' header of the forwarded request, if we are already overriding the body.

    Combining with fastify-formbody

    formbody expects the body to be returned as a string and not an object. Use the contentTypesToEncode option to pass in ['application/x-www-form-urlencoded']

    HTTP & HTTP2 timeouts

    This library has:

    • timeout for http set by default. The default value is 10 seconds (10000).
    • requestTimeout & sessionTimeout for http2 set by default.
      • The default value for requestTimeout is 10 seconds (10000).
      • The default value for sessionTimeout is 60 seconds (60000).

    When a timeout happens, 504 Gateway Timeout will be returned to the client.


    • [ ] support overriding the body with a stream
    • [ ] forward the request id to the other peer might require some refactoring because we have to make the unique (see hyperid).
    • [ ] Support origin HTTP2 push
    • [x] benchmarks




    npm i fastify-reply-from

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