Using ETag
Understand how to implement and use ETag headers in Python REST APIs to enable clients to cache responses effectively, reduce unnecessary data transfers, and handle optimistic concurrency control. This lesson guides you through generating ETags, handling If-None-Match and If-Match headers, and using Flask to create endpoints that respond conditionally based on resource state.
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An ETag, abbreviated from entity tag, is a header part of the HTTP standard. It allows a client to make conditional requests using its cache, limiting bandwidth and usage of server resources.
When a client sends a request to a server, the latter can reply with a response including an ETag header. Common methods of ETag generation include using a collision-resistant hash function of the resource’s content, a hash of the last modification timestamp, or even just a revision number.
The below terminal demonstrates a server reply with an ETag header. Run the terminal provided below to see the etag header in http response from http://httpbin.org/etag.
If-None-Match header
An application can use the ETag value to decide whether the page should be downloaded again using an If-None-Match header, as shown in the terminal below.
If the ETag of the URL matches the value given in the If-None-Match header, the HTTP status code returned is 304 Not Modified, and no ...