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Return JSON body in HTTP response in Go (Golang)

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Overview

Write method of the ResponseWriter interface in net/http package can be used to set the JSON body in an HTTP response

In GO a response is represented by the ResponseWriter Interface.  Here is the link to the interface –

https://golang.org/pkg/net/http/#ResponseWriter

ResponseWriter interface is used by an HTTP handler to construct an HTTP response. It provides three functions to set the response parameters

Write function can be used to set the response body. It takes a slice of bytes as input. Also, there is a Header function. This function can be used to set the content type of the response body using the Content-Type header. For eg in the case of the JSON response body, we need to set the Content-Type header as “application/json”.

w.Header().Set("Content-Type", "application/json")

Also, note that WriteHeader function can be used to set the HTTP status code for the response

Example

Let’s see an example of sending http status code and JSON response body

Below is the program for the same

package main

import (
	"encoding/json"
	"log"
	"net/http"
)

func main() {
	handler := http.HandlerFunc(handleRequest)
	http.Handle("/example", handler)
	http.ListenAndServe(":8080", nil)
}

func handleRequest(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(http.StatusCreated)
	w.Header().Set("Content-Type", "application/json")
	resp := make(map[string]string)
	resp["message"] = "Status Created"
	jsonResp, err := json.Marshal(resp)
	if err != nil {
		log.Fatalf("Error happened in JSON marshal. Err: %s", err)
	}
	w.Write(jsonResp)
	return
}

In the above program, this is how we create a JSON response. We use the json.Marshal function to convert the map[string]string into json bytes.

resp := make(map[string]string)
resp["message"] = "Status Created"
jsonResp, err := json.Marshal(resp)
if err != nil {
	log.Fatalf("Error happened in JSON marshal. Err: %s", err)
}
w.Write(jsonResp)

It then uses the Write function to return the JSON response body. The above code returns the below JSON response body back in response

{"message":"Status Created"}

Also, we are using the WriteHeader function to specify the 201 http status code.

Run the above program. It will start a server on 8080 port on your local machine. Now make the below curl call to the server

curl -v -X POST http://localhost:8080/example

Below will be the output

* Connected to localhost (::1) port 8080 (#0)
> POST /example HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.54.0
> Accept: */*
> 
< HTTP/1.1 201 Created
< Date: Sat, 10 Jul 2021 10:40:33 GMT
< Content-Length: 28
< Content-Type: text/plain; charset=utf-8
< 
* Connection #0 to host localhost left intact
{"message":"Status Created"}

As you can see from the output, it will correctly return the 201 status code along with the JSON body.

Also, check out our Golang advance tutorial Series - Golang Advance Tutorial