Return 400 (Bad Request) Status Code in http response in Go (Golang)

Overview

net/http package of golang provides the status code constants which could be used to return different status codes- https://golang.org/src/net/http/status.go

The same can also be used to return the 400 (Bad Request) HTTP status code.  The HTTP 400 status code is defined by the below constant

In this article, we will also see how to return a JSON body along with the 400 (Bad Request) Status Code

Program

Below is the program for the same

package main

import (
	"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.StatusBadRequest)
	return
}

Here we are using the WriteHeader function to specify the 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/1.1 400 Bad Request
< Date: Sat, 10 Jul 2021 05:50:32 GMT
< Content-Length: 0
< 
* Connection #0 to host localhost left intact

As you can see from the output, it will correctly return the 400 status code. If we also want to return the JSON error body, then below is the code 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.StatusBadRequest)
	w.Header().Set("Content-Type", "application/json")
	resp := make(map[string]string)
	resp["message"] = "Bad Request"
	jsonResp, err := json.Marshal(resp)
	if err != nil {
		log.Fatalf("Error happened in JSON marshal. Err: %s", err)
	}
	w.Write(jsonResp)
	return
}

The above code returns the below JSON request body back in response

{"message":"Bad Request"}

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/1.1 400 Bad Request
< Date: Sat, 10 Jul 2021 05:58:42 GMT
< Content-Length: 25
< Content-Type: text/plain; charset=utf-8
< 
* Connection #0 to host localhost left intact
{"message":"Bad Request"}

As you can see from the output, it correctly returns the 400 status code along with the body.

You can also directly pass 400 to the WriteHeader function to send the 400 response.

w.WriteHeader(400)

This also works correctly. Try it out.

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