Return 404 (Resource Not Found) Status Code in http response in Go (Golang)

Overview

http package of golang provides the status code constant 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 404 (Resource Not Found) http status code. The http 404 status code is defined by the below constant

http.StatusNotFound

In this article, we will also see how to return a JSON body along with the 404 (Resource Not Found) http status code

Program

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.StatusNotFound)
	w.Header().Set("Content-Type", "application/json")
	resp := make(map[string]string)
	resp["message"] = "Resource Not Found"
	jsonResp, err := json.Marshal(resp)
	if err != nil {
		log.Fatalf("Error happened in JSON marshal. Err: %s", err)
	}
	w.Write(jsonResp)
	return
}

Here we are using the WriteHeader function to specify the 404 http status code and uses the Write function to also return the response bodyThe above code returns the below JSON request body back in response

{"message":"Resource Not Found"}

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/1.1 404 Not Found
< Date: Sat, 10 Jul 2021 06:18:12 GMT
< Content-Length: 32
< Content-Type: text/plain; charset=utf-8
< 
* Connection #0 to host localhost left intact
{"message":"Resource Not Found"}

As you can see from the output, it correctly returns the 404 status code along with the body.

You can also directly pass 404 to the WriteHeader function to send the 404 response.

w.WriteHeader(404)

This also works correctly. Try it out.

net/http package of golang also provides a "NotFound" handler that could be used to return a 404 for a particular API every time.

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

This handler function return 404 status and below response body

404 page not found

Below is the simple program for the same

package main

import (
	"net/http"
)

func main() {
	http.HandleFunc("/example", http.NotFound)
	http.ListenAndServe(":8080", nil)
}

In the above program, we simply specified the NotFound handler for localhost:8080/example API as below

http.HandleFunc("/example", http.NotFound)

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

* Connected to localhost (::1) port 8080 (#0)
> POST /example HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.54.0
> Accept: */*
> 
< HTTP/1.1 404 Not Found
< Content-Type: text/plain; charset=utf-8
< X-Content-Type-Options: nosniff
< Date: Sat, 10 Jul 2021 06:23:41 GMT
< Content-Length: 19
< 
404 page not found
* Connection #0 to host localhost left intact

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