title: App Engine Backend with Google Cloud Messaging connection fails building release version with proguard
body: <p>I have an android app using GCM and an app backend in google app engine. Everything works fine in debug mode. In my IntentService "RegistrationIntentService" I get the token calling</p>
  
  <pre><code>InstanceID instanceID = InstanceID.getInstance(this);
            String token = instanceID.getToken(SENDER_ID,
                          GoogleCloudMessaging.INSTANCE_ID_SCOPE, null);
  sendRegistrationToServer(token);//send to app engine
  </code></pre>
  
  <p>and I pass it to app engine backend with</p>
  
  <pre><code>private void sendRegistrationToServer(String token) {
      //
      if (regService == null) {
          Registration.Builder builder = new Registration.Builder(AndroidHttp.newCompatibleTransport(), new AndroidJsonFactory(), null)
                  .setRootUrl("https://android-app-backend.appspot.com/_ah/api/");
                 //where android-app-backend corresponds to my own Project ID
  
          regService = builder.build();
      }
  
      try {
          regService.register(token).execute();
      } catch (IOException e) {
          e.printStackTrace();
      }
  }
  </code></pre>
  
  <p>It works fine also if a generate a signed APK disabling proguard</p>
  
  <pre><code>(minifyEnabled false)
  </code></pre>
  
  <p>but if I generate the APK enabling proguard I can get the token(registration id),but I cannot store it in the cloud.
  The android application log tells me</p>
  
  <pre><code>D/libc﹕ Forward DNS query to netd(h=*****************.appspot.com s=^)
  W/System.err   com.google.api.client.googleapis.json.GoogleJsonResponseException:
  404 Not Found
  W/System.err﹕ Not Found
  W/System.err﹕ at  com.google.api.client.googleapis.services.json.AbstractGoogleJsonClientRequest.newExceptionOnError(Unknown Source)
  W/System.err﹕ at com.google.api.client.googleapis.services.json.AbstractGoogleJsonClientRequest.newExceptionOnError(Unknown Source)
  W/System.err﹕ at com.google.api.client.googleapis.services.AbstractGoogleClientRequest$1.interceptResponse(Unknown Source)
  W/System.err﹕ at com.google.api.client.http.HttpRequest.execute(Unknown Source)
  W/System.err﹕ at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(Unknown Source)
  W/System.err﹕ at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(Unknown Source)
  W/System.err﹕ at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.execute(Unknown Source)
  W/System.err﹕ at com.example.android.RegistrationIntentService.a(Unknown Source)
  W/System.err﹕ at com.example.android.RegistrationIntentService.onHandleIntent(Unknown Source)
  W/System.err﹕ at android.app.IntentService$ServiceHandler.handleMessage(IntentService.java:65)
  W/System.err﹕ at android.os.Handler.dispatchMessage(Handler.java:99)
  W/System.err﹕ at android.os.Looper.loop(Looper.java:137)
  W/System.err﹕ at android.os.HandlerThread.run(HandlerThread.java:60)
  </code></pre>
  
  <p>My proguard file is the default file 'proguard-android.txt'.</p>
  
  <p>How can I fix that issue?</p>