Create http.Response instance with sample body string in golang

As suggested by Not_a_Golfer and JimB:

io.ReadCloser is an interface that is satisfied when a struct implements both the Read and the Close functions.

Fortunately, there is ioutil.NopCloser, which takes a io.Reader and wraps it in the nopCloser struct, which implements both Read and Close. However, its Close function does nothing as implied from the name.

Here is an example:

package main

import (
    "bytes"
    "fmt"
    "io/ioutil"
    "net/http"
)

func main() {
    t := http.Response{
        Body: ioutil.NopCloser(bytes.NewBufferString("Hello World")),
    }

    buff := bytes.NewBuffer(nil)
    t.Write(buff)

    fmt.Println(buff)
}

To play with the code, click here.

Further to the top answer, I have found that in order for the response to be treated as the genuine article by clients, it needs to be more fully formed. For a normal (200) response, I do the following:

body := "Hello world"
t := &http.Response{
  Status:        "200 OK",
  StatusCode:    200,
  Proto:         "HTTP/1.1",
  ProtoMajor:    1,
  ProtoMinor:    1,
  Body:          ioutil.NopCloser(bytes.NewBufferString(body)),
  ContentLength: int64(len(body)),
  Request:       req,
  Header:        make(http.Header, 0),
}

Then you can, for example, add headers (with a 401 status code, to ask for authorisation, say). req is the http.Request for which you are generating the response.