Issuing HTTP(S) Requests

Region ID

The REGION_ID is an abbreviated code that Google assigns based on the region you select when you create your app. The code does not correspond to a country or province, even though some region IDs may appear similar to commonly used country and province codes. Including REGION_ID.r in App Engine URLs is optional for existing apps and will soon be required for all new apps.

To ensure a smooth transition, we are slowly updating App Engine to use region IDs. If we haven't updated your Google Cloud project yet, you won't see a region ID for your app. Since the ID is optional for existing apps, you don't need to update URLs or make other changes once the region ID is available for your existing apps.

Learn more about region IDs.

This page describes how to issue HTTP(S) requests from your App Engine app.

For details on request size limits and which headers are sent in a URL Fetch request, see Outbound Requests.

Issuing an HTTP request

To issue an outbound HTTP request, use the http package as usual, but create your client using urlfetch.Client. urlfetch.Client returns an *http.Client that uses urlfetch.Transport, which is an implementation of the http.RoundTripper interface that makes requests using the URL Fetch API.

The following snippet demonstrates how to perform a basic HTTP GET request:

import (
	"fmt"
	"net/http"

	"google.golang.org/appengine"
	"google.golang.org/appengine/urlfetch"
)

func handler(w http.ResponseWriter, r *http.Request) {
	ctx := appengine.NewContext(r)
	client := urlfetch.Client(ctx)
	resp, err := client.Get("https://www.google.com/")
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	fmt.Fprintf(w, "HTTP GET returned status %v", resp.Status)
}

Issuing an HTTPS request

In the Go API, you do not need to explicitly secure your request. The underlying URL Fetch service validates the certificate of the host it is contacting by default, and rejects requests if the certificate does not match.

Disabling host certificate validation

To disable automatic host certificate validation, you can manually create a Transport and set AllowInvalidServerCertificate to true.

Issuing a request to another App Engine app

When issuing a request to another App Engine app, your App Engine app must assert its identity by adding the header X-Appengine-Inbound-Appid to the request.

What's next

Learn about the URL Fetch service, such as the headers that are sent in a URL Fetch request in Outbound Requests.