How to make Post Cacheable?

Being cacheable is one of architectural constraints of REST. GET requests should be cachable by default – until special condition arises. Usually, browsers treat all GET requests cacheable. POST requests are not cacheable by default but can be made cacheable if either an Expires header or a Cache-Control header with a directive, to explicitly allows caching, is added to the response. Responses to PUT and DELETE requests are not cacheable at all.

There are two main HTTP response headers that we can use to control caching behavior:

Expires

The Expires HTTP header specifies an absolute expiry time for a cached representation. Beyond that time, a cached representation is considered stale and must be re-validated with the origin server. To indicate that a representation never expires, a service can include a time up to one year in the future.

Expires: Fri, 20 May 2016 19:20:49 IST

Cache-Control

The header value comprises one or more comma-separated directives. These directives determine whether a response is cacheable, and if so, by whom, and for how long e.g. max-age or s-maxage directives.

Cache-Control: max-age=3600

Cacheable responses (whether to a GET or to a POST request) should also include a validator — either an ETag or a Last-Modified header.

ETag

An ETag value is an opaque string token that a server associates with a resource to uniquely identify the state of the resource over its lifetime. When the resource changes, the ETag changes accordingly.

ETag: "abcd1234567n34jv"

Last-Modified

Whereas a response’s Date header indicates when the response was generated, the Last-Modified header indicates when the associated resource last changed. The Last-Modified value cannot be later than the Date value.

Source : https://restfulapi.net/caching/

So let’s say that the client sends a request for some metadata, and we want the client to cache it for 1 hour:

GET /customers/metadata HTTP/1.1
Host: api.example.com
Accept: application/json
Accept-Language: en

To do this, we just add the Cache-Control header to our response:

HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: max-age=3600
Content-Length: 88
Etag: "6d82cbb050ddc7fa9cbb659014546e59"

{
  "languageCodes": [
    {"da":"Danish"},
    {"no":"Norwegian"},
    {"en":"English"}
  ]
}

Source: https://www.kennethlange.com/boost-your-rest-api-with-http-caching/