Enable Cross Domain XMLHttpRequest Request in Go Server


Howto

To enable cross-domain XHR requests in servers, we need to set the following header in request response:

Access-Control-Allow-Origin: *

The above header says all requests from any other domain are allowed.

To set the Access-Control-Allow-Origin header in Go server via standard net/http package, we can use the following code in request handler:

func myHandler(w http.ResponseWriter, r *http.Request) {
      // allow all XHR requests from other domains
      w.Header().Set("Access-Control-Allow-Origin", "*")
}

Just one line of code to make your Go server enable Cross-Origin Resource Sharing (CORS).

Complete Example

The following is complete sample code for servers supporting CORS and running on Google App Engine Go Standard Environment

serverjson.go | repository | view raw
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package servejson

import (
	"fmt"
	"net/http"
)

func init() {
	http.HandleFunc("/", servejson)
}

func servejson(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Access-Control-Allow-Origin", "*")
	fmt.Fprint(w, `{"a":"b","c":"d"}`)
}
app.yaml | repository | view raw
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runtime: go
api_version: go1

handlers:
  - url: /.*
    script: _go_app
Makefile | repository | view raw
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export PATH := $(PATH):$(realpath ../../../../../go_appengine/)
PROJECT_DIR=$(CURDIR)
PROJECT_ID=golden-operator-130720
PROJECT_VERSION=blogexample

default:
	@echo "\033[92mRun development web server ...\033[0m"
	@goapp serve

fmt:
	@echo "\033[92mGo fmt source code ...\033[0m"
	@goapp fmt *.go

deploy:
	goapp deploy -application ${PROJECT_ID} -version ${PROJECT_VERSION} ${PROJECT_DIR}
	@echo "\033[92mDeployed URL: http://${PROJECT_VERSION}.${PROJECT_ID}.appspot.com/\033[0m"

Tested on:

  • Google App Engine Go 1.6

References:

[1]
[2]Setting HTTP headers in Golang - Stack Overflow