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# Caching

The cache is shared across all users. If two users run a query with the same requests—even with different auth tokens—the cached results are still returned.

  • Example¹: If you request such as /api/v1/episodes?duration=>3000000 and a second request with /api/v1/episodes?duration=>3000000, the API will define as equals and will return the cached data.
  • Example²: If you request such as /api/v1/episodes?episode_num=1 and a second request with /api/v1/episodes?episode_num=2, the API will define as different and will create a cache for each one.

You can identify if a result has been cached by checking the ETag header on the API response.

# ETag

The ETag (or entity tag) HTTP response header is an identifier for a specific version of a resource. It lets caches be more efficient and save bandwidth, as a web server does not need to resend a full response if the content was not changed.

  • Syntax
ETag: W/"<etag_value>"
ETag: "<etag_value>"
  • Example
ETag: "33a64df551425fcc55e4d42a148795d9f25f89d4"
ETag: W/"0815"

# If-None-Match

On receiving the request for XYZ along with 'If-None-Match' header, the server side logic checks whether XYZ needs a new copy of the resource by comparing the current value of the ETag identifier on the server side and the one which is received in the request header.

  • If request's If-None-Match is same as currently generated/assigned value of ETag on the server, then status code 304 (Not Modified) with the empty body is sent back and the browser uses cached copy of XYZ.
  • If request's If-None-Match value doesn't match the currently generated/assigned value of ETag for XYZ then server sends back the new content in the body along with status code 200.

The 'ETag' header with the new value is also included in the response. The browser uses the new XYZ and updates its cache with the new data.

# References