How to complete the challenge `GET /api/todos (406)`

By Alan RichardsonPublished 2021-07-17

Some APIs will report an error when asked for a return format that they do not support. Other APIs will respond with a default. The API Challenges will respond with a 406 status code. We can test for this by sending a GET request for all todos but pass in an 'accept' format that the system does not support.

GET /api/todos (406)

When we issue a request with an accept header, we are asking for a specific content format in the response. But... if we ask for a format that is not supported then the system may respond with a 406 'NOT ACCEPTABLE' status code.

Issue a GET request on the /api/todos end point with an Accept header of application/gzip to receive a response with a 406 'NOT ACCEPTABLE' status code.

GET request asks for a response with all the todo items
- e.g. GET /api/todos to get all the todo items
406 is a success code, in this case it means the accept header is not supported by the system
add the X-CHALLENGER header to track progress

Basic Instructions

Issue a GET request to end point "/api/todos"
- if running locally that endpoint would be
  - https://apichallenges.com/api/todos
The request should have an Accept header with the value application/gzip
The request should have an X-CHALLENGER header to track challenge completion
The response status code should be 406 when all the details are valid.
Check the body of the message has JSON formatted error message response
Check the content-type header in the response has application/json matching the response body

Some systems may simply ignore the 'accept' header and return the response in the default format.

Try it now

GET /api/todos with an unsupported Accept header to trigger 406

Example Request

> GET /api/todos HTTP/1.1
> Host: apichallenges.com
> User-Agent: insomnia/2021.2.2
> Accept: application/gzip
> X-CHALLENGER: x-challenger-guid

Example Response

< HTTP/1.1 406 Not Acceptable
< Connection: close
< Date: Sat, 17 Jul 2021 12:21:37 GMT
< Content-Type: application/json
< Access-Control-Allow-Origin: *
< Access-Control-Allow-Headers: *
< X-Challenger: x-challenger-guid
< Server: Jetty(9.4.z-SNAPSHOT)
< Via: 1.1 vegur

Example Response body:

{
  "errorMessages": [
    "Unrecognised Accept Type"
  ]
}

Overview Video

Watch on YouTube: "Solution to Get all Todos in usupported format"

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Lessons Learned

406 Not Acceptable proves the route exists but cannot produce the requested media type.
Unsupported Accept values are content negotiation failures, not missing-resource failures.
Negative negotiation tests help expose whether an API ignores client preferences.
Structured +json values still need explicit support and are not aliases for plain application/json.

Suggested Experiments

Change Accept: application/gzip to Accept: application/xml and compare 406 Not Acceptable with a successful representation.
Try Accept: application/json;q=0, application/xml;q=0 to see whether refusing all normal todo formats leaves the server with no acceptable representation.
Try Accept: application/problem+json or Accept: application/*+json and compare structured JSON rejection with plain application/json.

Experiment with this endpoint

How to complete the challenge GET /api/todos (406)