Now that you've created your Go application on App Engine, let's extend it to search the public Google+ stream for gopher photos.

In order to make a Google+ API call, you first need to import the Google API Client Library for Go.

The Google API Client Library is located at code.google.com/p/google-api-go-client . By convention Go packages are named after their repository URLs, and are installed by the go tool in the $GOPATH directory.

1. Download the google-api-go-client package for Google+ API:

   /path/to/google_appengine/go get -v -d code.google.com/p/google-api-go-client/plus/v1
   

2. Go to the Google Developers Console and create a new project named goplus .
3. In the APIs and Auth pane, activate Google+ API .
4. In the Registered Apps pane, select the name of your app. If your app isn't registered, click Register App .

5. If you haven't done so already, create your application's API key by clicking Create new Key under Public API access . Next, look for your API key in the Key for browser applications or Key for server applications sections.

6. In the goplus directory, create a file named config.go with the following content, and replace YOUR_API_KEY with the api key you just generated.

   package goplus
   
   // apiKey is the Google API key of the project copied from the Google API Console.
   var apiKey = "YOUR_API_KEY"
   
   

7. In the goplus directory, create a file named gopher.go with the following content:

   package goplus
   
   import (
   	"net/http"
   
   	// Import appengine urlfetch package, that is needed to make http call to the api
   	"appengine"
   	"appengine/urlfetch"
   
   	// Import google api go client library
   	"code.google.com/p/google-api-go-client/googleapi/transport"
   	// Import Google+ package, the package will be named "plus"
   	"code.google.com/p/google-api-go-client/plus/v1"
   )
   
   // gopherFallback is the official gopher URL (in case we don't find any in the Google+ stream)
   const gopherFallback = "http://golang.org/doc/gopher/gophercolor.png"
   
   // init is called before the application start
   func init() {
   	// Register a handler for /gopher URLs.
   	http.HandleFunc("/gopher", gopher)
   }
   
   // gopher is an HTTP handler that searches Google+ for an activity
   // with a Gopher photo and redirects to the image thumbnail.
   func gopher(w http.ResponseWriter, r *http.Request) {
   	// Create appengine context, needed to do urlfetch call
   	c := appengine.NewContext(r)
   
   	// Create a new http client, supplying the API key we
   	// generated to identify our application, and the urlfetch
   	// transport necessary to make HTTP calls on App Engine
   	transport := &transport.APIKey{
   		Key:       apiKey,
   		Transport: &urlfetch.Transport{Context: c}}
   	client := &http.Client{Transport: transport}
   
   	// Create the plus service object with which we can make an API call
   	service, err := plus.New(client)
   	if err != nil {
   		// error creating the Google+ client
   		http.Error(w, err.Error(), http.StatusInternalServerError)
   		return
   	}
   
   	// Search the stream for "gopher" related activities
   	result, err := service.Activities.Search("#gopher").Do()
   	if err != nil {
   		// error searching Google+ for gopher
   		http.Error(w, err.Error(), http.StatusInternalServerError)
   		return
   	}
   
   	// Iterate through the activities search result until we find a photo or album attachment
   	for _, item := range result.Items {
   		for _, att := range item.Object.Attachments {
   			switch att.ObjectType {
   			case "photo":
   				// Redirect to the gopher thumbnail
   				http.Redirect(w, r, att.Image.Url, 302)
   				return
   			case "album":
   				http.Redirect(w, r, att.Thumbnails[0].Image.Url, 302)
   				return
   			}
   		}
   	}
   	// Fallback on the official gopher if we didn't find any gophers in the stream
   	http.Redirect(w, r, gopherFallback, http.StatusFound)
   }
   
   

   The gopher function does several things:

   1. Set up a plus service using the developer key,
   2. Call the Search method with the keyword "gopher",
   3. Scan the result, looking for a photo or album attachment, and
   4. Redirect the client to the first image URL found.

   The google-api-go-client provides a set of Go types with methods for interacting with the Google+ API as you would with any native package. These types are generated automatically using the Google APIs Discovery Service .

8. Visit http://localhost:8080/gopher in your browser.

You should be redirected to the most recent Gopher-related picture posted on Google+.

Next step: Deploy to App Engine