@opencode-ai/http-recorder

Record real Effect HTTP and WebSocket traffic once, then replay it from deterministic JSON cassettes.

Use it for provider integrations, retries, polling, multi-step flows, and any test where hand-written HTTP mocks hide too much of the real request shape.

Public beta. The API depends on Effect 4 beta and may change with Effect's unstable transport modules.

Install

bun add [email protected]
bun add -d @opencode-ai/http-recorder@beta @effect/vitest vitest

The package supports Node.js 22+ and Bun. It is not intended for browsers, workers, or Deno.

Effect 4.0.0-beta.74 has a known declaration error (SchemaErrorTypeId is missing). Until that upstream declaration is fixed, TypeScript consumers need:

{
  "compilerOptions": {
    "skipLibCheck": true
  }
}

Quick Start

import { assert, describe, it } from "@effect/vitest"
import { Effect, Schema } from "effect"
import { HttpClient, HttpClientRequest } from "effect/unstable/http"
import { HttpRecorder } from "@opencode-ai/http-recorder"

const User = Schema.Struct({
  id: Schema.Number,
  name: Schema.String,
})

const getUser = Effect.gen(function* () {
  const http = yield* HttpClient.HttpClient
  const response = yield* http.execute(HttpClientRequest.get("https://jsonplaceholder.typicode.com/users/1"))
  return yield* Schema.decodeUnknownEffect(User)(yield* response.json)
})

describe("getUser", () => {
  it.effect("loads a user", () =>
    Effect.gen(function* () {
      const user = yield* getUser

      assert.strictEqual(user.id, 1)
      assert.strictEqual(user.name, "Leanne Graham")
    }).pipe(Effect.provide(HttpRecorder.http("users/get-one"))),
  )
})

Run the test with Vitest. The first local run calls the real API and records:

bunx vitest run users.test.ts

test/fixtures/recordings/users/get-one.json

Later runs replay that cassette without contacting the upstream server. When CI=true, missing cassettes fail instead of recording.

flowchart TD
  Run[Run test] --> Recorded{Cassette recorded?}
  Recorded -->|Yes| Replay[Replay cassette]
  Recorded -->|No, local| Record[Call service and record cassette]
  Recorded -->|No, CI| Fail[Fail: cassette missing]

Application code does not need to know whether a response is live or replayed.

API

HttpRecorder.http(name, options?)
HttpRecorder.socket(name, options?)

That is the complete public API. http provides a fetch-backed recorded HttpClient. socket decorates a standard Effect Socket.Socket supplied beneath it.

WebSockets

WebSocket cassettes preserve one ordered transcript of client and server text or binary frames. Replay follows that chronology: server frames are released until the next recorded client frame, then replay waits for the application to send the matching frame before continuing.

import { assert, it } from "@effect/vitest"
import { NodeSocket } from "@effect/platform-node"
import { Effect, Layer } from "effect"
import { Socket } from "effect/unstable/socket"
import { HttpRecorder } from "@opencode-ai/http-recorder"

const echo = Effect.gen(function* () {
  const socket = yield* Socket.Socket
  const write = yield* socket.writer

  yield* socket.runString(
    (message) =>
      Effect.gen(function* () {
        assert.strictEqual(message, "hello")
        yield* write(new Socket.CloseEvent(1000))
      }),
    { onOpen: write("hello") },
  )
})

const recordedSocket = HttpRecorder.socket("echo/hello").pipe(
  Layer.provide(
    NodeSocket.layerWebSocket("wss://ws.postman-echo.com/raw", {
      closeCodeIsError: (code) => code !== 1000,
    }),
  ),
)

it.effect("exchanges WebSocket frames", () => echo.pipe(Effect.provide(recordedSocket)))

The application owns the WebSocket URL and protocols through normal Effect layer wiring. The recorder wraps that socket without duplicating its URL in recorder configuration. Provide separate socket layers for separate endpoints or concurrent connections.

Text frames use the same JSON-field and body redaction as HTTP bodies. Binary frames are stored losslessly as base64. Client and server frame kinds must match during replay.

Refresh A Cassette

Delete exactly the recordings you want to replace, then rerun their tests:

rm test/fixtures/recordings/users/get-one.json
bun run test users.test.ts

There is intentionally no public overwrite mode. Deletion makes the set of recordings being refreshed visible and reviewable.

Redaction

Secure defaults remove most headers and redact common credentials in headers, URLs, and JSON bodies. Extend those defaults at layer construction:

HttpRecorder.http("anthropic/messages", {
  redact: {
    headers: ["x-project-token"],
    allowRequestHeaders: ["anthropic-version"],
    queryParameters: ["session-id"],
    jsonFields: ["user_id"],
    url: (url) => url.replace(/\/accounts\/[^/]+/, "/accounts/{account}"),
    body: (body) => body.replaceAll(/usr_[a-z0-9]+/g, "usr_redacted"),
  },
})

Before writing, the recorder scans the complete cassette for common credential formats and values from credential-like environment variables. Unsafe cassettes fail without replacing an existing recording.

Redaction is defense in depth, not a substitute for review. Inspect cassette diffs before committing them.

Matching And Ordering

A cassette contains an ordered sequence of interactions. The first runtime request is checked against the first recorded request, the second against the second, and so on.

This strict ordering correctly models repeated identical requests whose responses change, including retries, polling, and cache tests. JSON object keys are canonicalized before matching.

Concurrent requests are recorded in request-start order even when their responses complete out of order.

Supply a custom equivalence rule when a request contains intentionally volatile data:

HttpRecorder.http("events/create", {
  match: (incoming, recorded) =>
    incoming.method === recorded.method && new URL(incoming.url).pathname === new URL(recorded.url).pathname,
})

Configuration

interface RecorderOptions {
  readonly directory?: string
  readonly metadata?: Record<string, unknown>
  readonly redact?: RedactOptions
  readonly match?: RequestMatcher
}

directory defaults to <cwd>/test/fixtures/recordings.

Cassettes

Cassettes are readable JSON files intended to be committed with your tests. HTTP interactions are stored in request order. WebSocket cassettes preserve the observed order of client and server frames. Text stays readable; binary bodies and frames are stored losslessly as base64.

Current Limits

• Responses are buffered while recording and replaying, so this beta is not suitable for tests that assert streaming timing, cancellation, or backpressure.
• WebSocket replay preserves frame chronology and content, not real network timing or backpressure.
• WebSocket V1 cassettes do not reproduce terminal close codes, close reasons, or transport failures. Failed and interrupted live runs are not recorded.
• WebSocket transcripts are retained in memory until the connection finishes; avoid using this beta for unbounded sessions.
• The package currently requires the exact Effect beta listed above.
• Cassette format version 1 has no migration tooling yet.

License

MIT