Hi All, In the current cache mediator implementation, cache control headers and ETag haven't been considered when serving responses through the cache mediator. Basically, it caches all responses and responds with same headers for the subsequent requests. I am planning to improve the current cache mediator with the following features:
- Honor ETag header - Honor "no-cache" & "no-store" cache-control header. - Honor "max-age" cache-control header. - Add Age header based on "max-age" cache-control header when returning the cached response. *1. ETag support:* If ETag header is present in the response, subsequent requests need to be issued with the "If-None-Match" header(with ETag value) and if the requested resource is modified from the last response fetched time, a new modified response will be returned with new ETag. And this new response needs to be cached. If it is not modified, the server returns a "304 Not Modified" response. In that case, the cached response can be reused. Flow: - Cache mediator receives a request. - Check whether a cached response is available for the same request. - If it is available and ETag is present in the cached response, make a request with "If-None-Match" header with the ETag value. - If the server returns "304 Not Modified" response returns the cached response to the user. - If the server returns a new modified response(200 OK response) then cache the newly returned response. *2. Honor "no-cache" and "no-store" header* - If the "no-cache" header is present in the response it indicates that the returned response can’t be used to satisfy a subsequent request to the same URL without first checking with the server if the response has changed. So before responding with the cached response cache mediator should validate the response with ETag. This can be supported through the ETag support. - If the "no-store" header is present in the response, Cache mediator should not cache the returned response. *3. Honor "max-age" cache-control header* If the "max-age" header presents in the response it specifies the maximum time in seconds that the fetched response is allowed to be reused from the time of the request. So the response should be cached and reused within the max-age time limit. So the Cache mediator should honor max-age instead of timeout configuration if it is less than the timeout configuration. 4. *Include an ‘Age’ header with the response* Cache mediator should return the true TTL value of a response without altering the value of the cache-control max-age header returned by the back-end. Flow: - Calculate the TTL using response fetched time and max-age header - Set the Age header to the cached response before returning it to the user. [1]. https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/http-caching [2]. https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html Thanks, Keerthika. -- <dev-requ...@wso2.org> Keerthika Mahendralingam Software Engineer Mobile :+94 (0) 776 121144 <+94%2077%20612%201144> keerth...@wso2.com WSO2, Inc. lean . enterprise . middleware
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