How to cache http.Response in golang?

The easiest way is to use httputil.DumpResponse and http.ReadResponse.

See here for an example. (You have to copy the code onto your local machine and run it there, because the Playground doesn't allow I/O)

The first dumps your request as-received, optionally also dumping the body, to an in-memory []byte that you can then write to disk. Later you can read the response back from disk (or where ever you stored it) and wrap it in an bufio.Reader, which you pass to http.ReadResponse.

ReadResponse takes a *http.Request as second parameter that is used as the value for the Request field of the response. If nil is given, the returned Response will have GET request in it's Request field.

... Or use https://github.com/lox/httpcache. An RFC7234 compliant golang http.Handler for caching HTTP responses