Is it possible to cache POST methods in HTTP?

http post http-caching
flybywire picture flybywire · Mar 9, 2009 · Viewed 93.5k times · Source

With very simple caching semantics: if the parameters are the same (and the URL is the same, of course), then it's a hit. Is that possible? Recommended?

Answer

Diomidis Spinellis picture Diomidis Spinellis · Mar 9, 2009

The corresponding RFC 2616 in section 9.5 (POST) allows the caching of the response to a POST message, if you use the appropriate headers.

Responses to this method are not cacheable, unless the response includes appropriate Cache-Control or Expires header fields. However, the 303 (See Other) response can be used to direct the user agent to retrieve a cacheable resource.

Note that the same RFC states explicitly in section 13 (Caching in HTTP) that a cache must invalidate the corresponding entity after a POST request.

Some HTTP methods MUST cause a cache to invalidate an entity. This is either the entity referred to by the Request-URI, or by the Location or Content-Location headers (if present). These methods are:

  - PUT
  - DELETE
  - POST

It's not clear to me how these specifications can allow meaningful caching.

This is also reflected and further clarified in RFC 7231 (Section 4.3.3.), which obsoletes RFC 2616.

Responses to POST requests are only cacheable when they include
explicit freshness information (see Section 4.2.1 of [RFC7234]).
However, POST caching is not widely implemented. For cases where an origin server wishes the client to be able to cache the result of a POST in a way that can be reused by a later GET, the origin server MAY send a 200 (OK) response containing the result and a Content-Location header field that has the same value as the POST's effective request URI (Section 3.1.4.2).

According to this, the result of a cached POST (if this ability is indicated by the server) can be subsequently used for as the result of a GET request for the same URI.

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