Configure CORS for a Go backend

#go #programming #tutorial

According to mozilla.org, Cross-Origin Resource Sharing (CORS) is an HTTP-header based mechanism that allows a server to indicate any origins (domain, scheme, or port) other than its own from which a browser should permit loading resources.

When writing a backend for your app using golang in the local environment you can perform requests to your APIs without the need to configure CORS, but once you deploy the backend you will require CORS or else you will face errors communicating with the backend.

This tutorial will help you fix this error in a go backend that uses gin framework.

We will first download and install the cors middleware using the following line

go get github.com/gin-contrib/cors

Then now import to your main.go file

import "github.com/gin-contrib/cors"

Now let's add cors middleware

Add the following code in the main.go file

func main() {
    r := gin.Default()
    config := cors.DefaultConfig()
    config.AllowAllOrigins = true
    config.AllowMethods = []string{"POST", "GET", "PUT", "OPTIONS"}
    config.AllowHeaders = []string{"Origin", "Content-Type", "Authorization", "Accept", "User-Agent", "Cache-Control", "Pragma"}
    config.ExposeHeaders = []string{"Content-Length"}
    config.AllowCredentials = true
    config.MaxAge = 12 * time.Hour

    r.Use(cors.New(config))
}

Your main.go file should now look like below now;

package main

import (
    "time"

    "github.com/gin-contrib/cors"
    "github.com/gin-gonic/gin"
    "github.com/username/appname/controllers"
)

func init() {
    //initialize app
}

func main() {
    r := gin.Default()
    config := cors.DefaultConfig()
    config.AllowAllOrigins = true
    config.AllowMethods = []string{"POST", "GET", "PUT", "OPTIONS"}
    config.AllowHeaders = []string{"Origin", "Content-Type", "Authorization", "Accept", "User-Agent", "Cache-Control", "Pragma"}
    config.ExposeHeaders = []string{"Content-Length"}
    config.AllowCredentials = true
    config.MaxAge = 12 * time.Hour

    r.Use(cors.New(config))

        //Add endpoints here
    r.POST("/ping/", controllers.Pong)

    r.Run()
}

You can now deploy and run your go backend successfully on a serverless platform like railway easily and CORS error should be fixed now.

Have any questions?

Top comments (3)

Ushakov Michael • Jun 12 '23

Nice article, but we also made some research and could automatically set CORS headers when register new routes in router but actually for gorilla/mux not for gin, you could see our article about auto CORS setting: dev.to/evillord666/auto-cors-prefl...

Benard Mseti • Jun 13 '23

Thank you for your feedback and for sharing your article. I appreciate your input and the effort you put into your research.

While my article focused specifically on CORS in the context of the Gin framework, it's great to see that you have explored the topic in relation to gorilla/mux. Different frameworks often have their own unique approaches and solutions.

I will definitely take a look at your article to learn more about auto CORS setting with gorilla/mux. Thank you for bringing it to my attention, and I'm glad we can exchange knowledge on this.