How to Use ResponseWriter in Go

Use http.ResponseWriter as the first argument in your HTTP handler function to write status codes, headers, and the response body directly to the client.

func handler(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(http.StatusOK)
	w.Header().Set("Content-Type", "text/plain")
	w.Write([]byte("Hello, World!"))
}

1. Define a handler function accepting w http.ResponseWriter and r *http.Request.
2. Call w.WriteHeader(statusCode) to set the HTTP status before writing the body.
3. Use w.Header().Set(key, value) to add custom headers.
4. Write the response content using w.Write([]byte("content")).

The ResponseWriter is the tool your Go server uses to send data back to a web browser. Think of it as the return envelope where you write the message, set the postage (status code), and add labels (headers) before mailing it. You use it in every function that handles a web request to tell the user what happened.