Record/inspect/replay fetch and WebSocket sessions

For offline testing

These implementations are not specific to @exodus/test and can be used separately

Zero-dependencies, bundleable

Replayers can run in V8 / JavaScriptCore / Hermes even with no network API implemented at all

import { fetchRecorder, fetchReplayer, WebSocketRecorder, WebSocketReplayer, prettyJSON } from '@exodus/replay'

Generated logs are human-readable

fetchRecorder(log[, { fetch }])

Returns a fetch implementation that appends all requests to the provided log array

log is expected to be an array and is mutated by appending new requests

If a base fetch implementation is not passed, global fetch is used as the base

That can be overriden, e.g. fetchRecorder(log, { fetch: require('node-fetch') })

fetchReplayer(log)

Returns a fetch implementation that replies with requests from the provided log array

Requests are served by "first matching" order and are discarded from an internal log clone

log is expected to be an array and is not mutated

WebSocketRecorder(log[, { WebSocket }])

Returns a WebSocket implementation that appends all sessions to the provided log array

log is expected to be an array and is mutated by appending new sessions

If a base WebSocket implementation is not passed, global WebSocket is used as the base

That can be overriden, e.g. WebSocketRecorder(log, { WebSocket: require('ws') })

WebSocketReplayer(log[, { interval = 0 }])

Returns a WebSocket implementation that replies with sessions from the provided log array

Sessions are served by "first matching" order and are discarded from an internal log clone

log is expected to be an array and is not mutated

Optionally, interval can be used to control replay speed:

• interval = 0 for immediate event firing without delays (default)

• interval = Infinity for event timing matching the original recording

• interval = number for delay between events of Math.min(number, recorededDelay)

prettyJSON(data, { width = 120 })

Use it to pretty-print logs: prettyJSON(log)

Like JSON.stringify(), but with pretty-printing for readability and ease if inspection

The output is parse-able with JSON.parse()

For simplicity, fitting into width is not guaranteed, but the output is stable between runs

Samples

fetch recording

{
  "request": {
    "resource": "https://jsonplaceholder.typicode.com/users/2",
    "options": { "headers": [["accept", "application/json"]] }
  },
  "status": 200,
  "statusText": "OK",
  "ok": true,
  "headers": [
    ...
    ["connection", "keep-alive"],
    ["content-encoding", "br"],
    ["content-type", "application/json; charset=utf-8"],
    ["date", "Sat, 03 Aug 2024 16:57:51 GMT"],
    ...
  ],
  "url": "https://jsonplaceholder.typicode.com/users/2",
  "redirected": false,
  "type": "basic",
  "bodyType": "json",
  "body": {
    "id": 2,
    "name": "Ervin Howell",
    "username": "Antonette",
    "email": "Shanna@melissa.tv",
    "address": {
      "street": "Victor Plains",
      "suite": "Suite 879",
      "city": "Wisokyburgh",
      "zipcode": "90566-7771",
      "geo": { "lat": "-43.9509", "lng": "-34.4618" }
    },
    "phone": "010-692-6593 x09125",
    "website": "anastasia.net",
    "company": {
      "name": "Deckow-Crist",
      "catchPhrase": "Proactive didactic contingency",
      "bs": "synergize scalable supply-chains"
    }
  }
}

WebSocket recording

{
  "url": "wss://javascript.info/article/websocket/demo/hello",
  "log": [
    { "type": "get readyState", "at": 24, "value": 0 },
    { "type": "open", "at": 426 },
    { "type": "get readyState", "at": 426, "value": 1 },
    { "type": "get bufferedAmount", "at": 427, "value": 0 },
    { "type": "send()", "at": 427, "data": "Hi there" },
    { "type": "get bufferedAmount", "at": 427, "value": 8 },
    { "type": "message", "at": 543, "data": "Hello from server, there!" },
    { "type": "close()", "at": 543 },
    { "type": "get readyState", "at": 543, "value": 2 },
    { "type": "close", "at": 661, "code": 1005, "reason": "", "wasClean": true },
    { "type": "get readyState", "at": 661, "value": 3 }
  ]
}