Http POST request with body Go - http

Question

I want to construct a HTTP POST request with a body using Go net/http library.
The function I am using to construct the http request is the following: docs
http.NewRequest(method string, url string, body io.Reader)
I came up with 2 solutions, but I am trying to see which one is more idiomatic and extensible to support different body configurations.
Solution #1
bytesObj := []byte(`{"key":"value"}`)
body := bytes.NewBuffer(bytesObj)
Solution #2
bodyMap := map[string]string{"key":"value"}
bodyBytes, _ := json.Marshal(bodyMap)
body := bytes.NewBuffer(bodyBytes)
Ideally, I will move the code to a helper function that way I can customize the construction of the body. The helper function will be something like
func constructBody(someArgument) io.Reader {
return bodyHere
}

Answer 1

If the body is already string, options #1 is more compelling to me.
If you are only working with a key -> value with only string, option #2 is better.
But this will become cumbersome when you have nested struct
But most of the time in my experience we are dealing with struct. I like to make the struct closer to where the http call happened.
func main() {
ctx := context.Background()
body := struct {
Key string `json:"key"`
}{
Key: "value",
}
out, err := json.Marshal(body)
if err != nil {
log.Fatal(err)
}
req, err := http.NewRequest("POST", "http://example.com", bytes.NewBuffer(out))
if err != nil {
log.Fatal(err)
}
req = req.WithContext(ctx)
http.DefaultClient.Do(req)
}
And if the struct is used in multiple places, you can make a package level struct.

Answer 2

To have it more reusable, you could create a jsonReaderFactory, which just takes a few lines of code:
func jsonReaderFactory(in interface{}) (io.Reader, error) {
buf := bytes.NewBuffer(nil)
enc := json.NewEncoder(buf)
err := enc.Encode(in)
if err != nil {
return nil, fmt.Errorf("creating reader: error encoding data: %s", err)
}
return buf, nil
}
Example on playground