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Tutorial

Learn async APIs

Some API work can't finish while the client waits: a report that takes two minutes, a payment that settles an hour later, prices that keep changing. Async APIs split the request from the result, and that split is where their bugs live: results fetched too early, webhooks delivered twice, streams that never end.

The API testing course's async lesson covers the ideas in one page. These lessons go deeper, one pattern at a time. Every example was run against the jobs, webhook and streaming endpoints at https://api.testingapis.com, and the timings and responses shown are the ones they produced. For two-way connections, see the WebSocket tutorial. These endpoints need a free account; the examples and Send buttons work once you're signed in.

8 lessons3 levelsFree

Beginner

3 lessons

Why some work can't finish inside one request, and the job pattern most APIs use for it.

  1. 01Why APIs go asyncTimeouts, long work, and the four patterns that get around them.
  2. 02Polling a job: 202 Accepted done rightLocation, Retry-After, status fields, and a client that waits politely.
  3. 03Testing async jobsEvery state a job can end in, cancelling, early results and tests that don't sleep.

Intermediate

3 lessons

Webhooks from both sides: capturing them, checking their signatures, and surviving retries.

  1. 04Capturing webhooks with a binSee exactly what a webhook sender sends, and make the receiver fail on purpose.
  2. 05Verifying webhook signaturesThree signature formats, the raw body, timestamps, and comparing safely.
  3. 06Webhook delivery: retries, duplicates and orderAnswer fast, process once, and cope with events arriving twice or out of order.

Advanced

2 lessons

Responses that keep arriving: Server-Sent Events, NDJSON and chunked streams, and how to test them.

  1. 07Server-Sent EventsThe event format, EventSource, resuming with Last-Event-ID, and the reconnect loop.
  2. 08Streaming JSON and chunked responsesNDJSON line by line, arrays that arrive in pieces, and timeouts for slow bodies.