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@gzaripov/talkback v2.1.0

A node.js HTTP proxy that records and playbacks requests


Record and playback HTTP requests.
Talkback is a pure javascript standalone HTTP proxy. As long as you have node.js in your environment, you can run Talkback to record requests from applications written in any language/framework.
You can use it to accelerate your integration tests or running your application against mocked HTTP servers.

Read more about the reasoning behind talkback on 10Pines blog.

npm version Build Status


npm install talkback


Talkback is pretty easy to setup.
Define which host it will be proxying, which port it should listen to and where to find and save tapes.

When a request arrives to talkback, it will try to match it against a previously saved tape and quickly return the tape's response.
If no tape matches the request, it will forward it to the origin host, save the tape to disk for future uses and return the response.

const talkback = require("talkback");

const opts = {
  host: "",
  record: talkback.Options.RecordMode.NEW,
  port: 5544,
  path: "./my-tapes"
const server = talkback(opts);
server.start(() => console.log("Talkback Started"));


Returns an unstarted talkback server instance.


hostStringWhere to proxy unknown requests
portStringTalkback port8080
pathStringPath where to load and save tapes./tapes/
httpsObjectHTTPS server optionsDefaults
recordString \| FunctionSet record mode. More infoRecordMode.NEW
nameStringServer nameDefaults to host value
tapeNameGeneratorFunctionCustomize how a tape name is generated for new tapes.null
ignoreHeaders[String]List of headers to ignore when matching tapes. Useful when having dynamic headers like cookies or correlation ids['content-length', 'host]
ignoreQueryParams[String]List of query params to ignore when matching tapes. Useful when having dynamic query params like timestamps[]
ignoreBodyBooleanShould the request body be ignored when matching tapesfalse
bodyMatcherFunctionCustomize how a request's body is matched against saved tapes. More infonull
urlMatcherFunctionCustomize how a request's URL is matched against saved tapes. More infonull
responseDecoratorFunctionModify responses before they're returned. More infonull
fallbackModeString \| FunctionFallback mode for unknown requests when recording is disabled. More infoFallbackMode.NOT_FOUND
silentBooleanDisable requests information console messages in the middle of requestsfalse
summaryBooleanEnable exit summary of new and unused tapes at exit. More infotrue
debugBooleanEnable verbose debug informationfalse

HTTPS options

enabledBooleanEnables HTTPS serverfalse
keyPathStringPath to the key filenull
certPathStringPath to the cert filenull


Starts the HTTP server and if provided calls callback after the server has successfully started.


Stops the HTTP server.


Tapes can be freely edited to match new requests or return a different response than the original. They are loaded recursively from the path directory at startup.
They use the JSON5 format. JSON5 is an extensions to the JSON format that allows for very neat features like comments, trailing commas and keys without quotes.


All tapes have the following 3 properties:

  • meta: Stores metadata about the tape.
  • req: Request object. Used to match incoming requests against the tape.
  • res: Response object. The HTTP response that will be returned in case the tape matches a request.

You can freely edit any part of the tape, and even add your own properties to meta.
Since tapes are only loaded on startup, any changes to a tape requires a server restart to be applied.

File Name

New tapes will be created under the path directory with the name unnamed-n.json5, where n is the tape number.
Tapes can be renamed at will, for example to give some meaning to the scenario the tape represents.
If a custom tapeNameGenerator is provided, it will be called to produce an alternate file path under path that can be based on the tape contents. Note that the file extension .json5 will be appended automatically.

function nameGenerator(tapeNumber, tape) {
  // organize in folders by request method
  // e.g. tapes/GET/unnamed-1.json5
  //      tapes/GET/unnamed-3.json5
  //      tapes/POST/unnamed-2.json5
  return path.join(`${tape.req.method}`, `unnamed-${tapeNumber}`)

Request and Response body

If the content type of the request or response is considered human readable and uncompressed, the body will be saved in plain text.
Otherwise, the body will be saved as a Base64 string, allowing to save binary content.

Pretty Printing

If the request or response have a JSON content-type, their body will be pretty printed as an object in the tape for easier readability.
This means differences in formatting are ignored when comparing tapes, and any special formatting in the response will be lost.

Recording Modes

Talkback proxying and recording behavior can be controlled through the record option.
This option accepts either one of the possible recording modes to be used for all requests or a function that takes the request as a parameter and returns a valid recording mode.

There are 3 possible recording modes:

NEWIf no tape matches the request, proxy it and save the response to a tape
OVERWRITEAlways proxy the request and save the response to a tape, overwriting any existing one
DISABLEDIf a matching tape exists, return it. Otherwise, don't proxy the request and use fallbackMode for the response

The fallbackMode option lets you choose what do you want Talkback to do when recording is disabled and an unknown request arrives.
Same as with record, this option accepts either one of the possible modes values to be used for all requests or a function that takes the request as a parameter and returns a mode.

There are 2 possible fallback modes:

NOT_FOUNDLog an error and return a 404 response
PROXYProxy the request to host and return its response, but don't create a tape

It is recommended to disable recording when using talkback for test running. This way, there are no side-effects and broken tests fail faster.

Talkback exports constants for the different options values:

  const talkback = require("talkback")
  const opts = {
    record: talkback.Options.RecordMode.OVERWRITE,
    fallbackMode: talkback.Options.FallbackMode.PROXY

Custom request body matcher

By default, in order for a request to match against a saved tape, both request and tape need to have the exact same body.
There might be cases were this rule is too strict (for example, if your body contains time dependent bits) but enabling ignoreBody is too lax.

Talkback lets you pass a custom matching function as the bodyMatcher option.
The function will receive a saved tape and the current request, and it has to return whether they should be considered a match on their body.
Body matching is the last step when matching a tape. In order for this function to be called, everything else about the request should match the tape too (url, method, headers).
The bodyMatcher is not called if tape and request bodies are already the same.


function bodyMatcher(tape, req) {
    if (tape.meta.tag === "fake-post") {
      const tapeBody = JSON.parse(tape.req.body.toString());
      const reqBody = JSON.parse(req.body.toString());

      return tapeBody.username === reqBody.username;
    return false;

In this case we are adding our own tag property to the saved tape meta object. This way, we are only using the custom matching logic on some specific requests, and can even have different logic for different categories of requests.
Note that both the tape's and the request's bodies are Buffer objects.

Custom request URL matcher

Similar to the bodyMatcher, there's the urlMatcher option, which will let you customize how a request and a tape are matched on their URL.


function urlMatcher(tape, req) {
    if (tape.meta.tag === "user-info") {
      // Match if URL is of type /users/{username}
      return !!req.url.match(/\/users\/[a-zA-Z-0-9]+/);
    return false;

Custom response decorator

If you want to add a little bit of dynamism to the response coming from a matching existing tape or adjust the response that the proxied server returns, you can do so by using the responseDecorator option.
This can be useful for example if your response needs to contain an ID that gets sent on the request, or if your response has a time dependent field.

The function will receive a copy of the matching tape and the in-flight request object, and it has to return the modified tape. Note that since you're receiving a copy of the matching tape, modifications that you do to it won't persist between different requests.
Talkback will also update the Content-Length header if it was present in the original response.


We're going to hit an /auth endpoint, and update just the expiration field of the JSON response that was saved in the tape to be a day from now.

function responseDecorator(tape, req) {
  if (tape.meta.tag === "auth") {
    const tapeBody = JSON.parse(tape.res.body.toString())
    const expiration = new Date()
    expiration.setDate(expiration.getDate() + 1)
    const expirationEpoch = Math.floor(expiration.getTime() / 1000)
    tapeBody.expiration = expirationEpoch

    const newBody = JSON.stringify(tapeBody)
    tape.res.body = Buffer.from(newBody)
  return tape

In this example we are also adding our own tag property to the saved tape meta object. This way, we are only using the custom logic on some specific requests, and can even have different logic for different categories of requests.
Note that both the tape's and the request's bodies are Buffer objects and they should be kept as such.

Exit summary

If you are using Talkback for your test suite, you will probably have tons of different tapes after some time. It can be difficult to know if all of them are still required.
To help, when talkback exits, it will print a list of all the tapes that have NOT been used and a list of all the new tapes. If your test suite is green, you can safely delete anything that hasn't been used.

===== SUMMARY (My Server) =====
New tapes:
- unnamed-4.json5
Unused tapes:
- not-valid-request.json5
- user-profile.json5

This can be disabled with the summary option.




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