Implement backend discovery.

The mechanism is the following:

Each android libary that provides a backend needs to implement a
`BackendFactory` and register it in its manifest. Runtime will
discover it via manifest and create the backend via the factory,
providing `CreationContext` to it.

Author: vkryachko

transport/transport-backend-cct/src/main/AndroidManifest.xml

@@ -14,8 +14,18 @@
 
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="com.google.android.datatransport.backend.cct">
-  <!--Although the *SdkVersion is captured in gradle build files, this is required for non gradle builds-->
-  <!--<uses-sdk android:minSdkVersion="14"/>-->
+    <!--Although the *SdkVersion is captured in gradle build files, this is required for non gradle builds-->
+    <!--<uses-sdk android:minSdkVersion="14"/>-->
 
-  <uses-permission android:name="android.permission.INTERNET" />
+    <uses-permission android:name="android.permission.INTERNET" />
+
+    <application>
+        <service
+            android:name="com.google.android.datatransport.runtime.backends.TransportBackendDiscovery"
+            android:exported="false">
+            <meta-data
+                android:name="backend:com.google.android.datatransport.cct.CctBackendFactory"
+                android:value="cct" />
+        </service>
+    </application>
 </manifest>

transport/transport-backend-cct/src/main/java/com/google/android/datatransport/cct/CctBackendFactory.java

@@ -0,0 +1,51 @@
+// Copyright 2018 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.android.datatransport.cct;
+
+import android.support.annotation.Keep;
+import android.support.annotation.VisibleForTesting;
+import com.google.android.datatransport.runtime.backends.BackendFactory;
+import com.google.android.datatransport.runtime.backends.CreationContext;
+import com.google.android.datatransport.runtime.backends.TransportBackend;
+
+@Keep
+public class CctBackendFactory implements BackendFactory {
+  private static final String URL = mergeStrings("hts/pa.ogepscmlgbth", "tp:/lygolai.o/o/ac");
+
+  @Override
+  public TransportBackend create(CreationContext creationContext) {
+    return new CctTransportBackend(
+        URL, creationContext.getWallClock(), creationContext.getMonotonicClock());
+  }
+
+  @VisibleForTesting
+  static String mergeStrings(String part1, String part2) {
+    int sizeDiff = part1.length() - part2.length();
+    if (sizeDiff < 0 || sizeDiff > 1) {
+      throw new IllegalArgumentException("Invalid input received");
+    }
+
+    StringBuilder url = new StringBuilder(part1.length() + part2.length());
+
+    for (int i = 0; i < part1.length(); i++) {
+      url.append(part1.charAt(i));
+      if (part2.length() > i) {
+        url.append(part2.charAt(i));
+      }
+    }
+
+    return url.toString();
+  }
+}

transport/transport-backend-cct/src/main/java/com/google/android/datatransport/cct/GoogleTransportBackend.java renamed to transport/transport-backend-cct/src/main/java/com/google/android/datatransport/cct/CctTransportBackend.java

@@ -15,22 +15,19 @@
 package com.google.android.datatransport.cct;
 
 import android.os.Build;
-import android.support.annotation.VisibleForTesting;
 import com.google.android.datatransport.cct.proto.AndroidClientInfo;
 import com.google.android.datatransport.cct.proto.BatchedLogRequest;
 import com.google.android.datatransport.cct.proto.ClientInfo;
 import com.google.android.datatransport.cct.proto.LogEvent;
 import com.google.android.datatransport.cct.proto.LogRequest;
 import com.google.android.datatransport.cct.proto.LogResponse;
 import com.google.android.datatransport.cct.proto.QosTierConfiguration;
-import com.google.android.datatransport.runtime.BackendRequest;
-import com.google.android.datatransport.runtime.BackendResponse;
-import com.google.android.datatransport.runtime.BackendResponse.Status;
 import com.google.android.datatransport.runtime.EventInternal;
-import com.google.android.datatransport.runtime.TransportBackend;
+import com.google.android.datatransport.runtime.backends.BackendRequest;
+import com.google.android.datatransport.runtime.backends.BackendResponse;
+import com.google.android.datatransport.runtime.backends.BackendResponse.Status;
+import com.google.android.datatransport.runtime.backends.TransportBackend;
 import com.google.android.datatransport.runtime.time.Clock;
-import com.google.android.datatransport.runtime.time.UptimeClock;
-import com.google.android.datatransport.runtime.time.WallTimeClock;
 import com.google.protobuf.ByteString;
 import com.google.protobuf.InvalidProtocolBufferException;
 import java.io.ByteArrayOutputStream;
@@ -50,9 +47,9 @@
 import java.util.logging.Logger;
 import java.util.zip.GZIPOutputStream;
 
-public class GoogleTransportBackend implements TransportBackend {
+final class CctTransportBackend implements TransportBackend {
 
-  private static final Logger LOGGER = Logger.getLogger(GoogleTransportBackend.class.getName());
+  private static final Logger LOGGER = Logger.getLogger(CctTransportBackend.class.getName());
   private static final int CONNECTION_TIME_OUT = 30000;
   private static final int READ_TIME_OUT = 40000;
   private static final String CONTENT_ENCODING_HEADER_KEY = "Content-Encoding";
@@ -80,17 +77,12 @@ private static URL parseUrlOrThrow(String url) {
     }
   }
 
-  @VisibleForTesting
-  GoogleTransportBackend(String url, Clock wallTimeClock, Clock uptimeClock) {
+  CctTransportBackend(String url, Clock wallTimeClock, Clock uptimeClock) {
     this.endPoint = parseUrlOrThrow(url);
     this.uptimeClock = uptimeClock;
     this.wallTimeClock = wallTimeClock;
   }
 
-  public GoogleTransportBackend() {
-    this("https://play.googleapis.com/log/batch", new WallTimeClock(), new UptimeClock());
-  }
-
   @Override
   public EventInternal decorate(EventInternal eventInternal) {
     return eventInternal

transport/transport-backend-cct/src/test/java/com/google/android/datatransport/cct/CctBackendFactoryTest.java

@@ -0,0 +1,47 @@
+// Copyright 2018 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.android.datatransport.cct;
+
+import static com.google.common.truth.Truth.assertThat;
+import static org.junit.Assert.assertThrows;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class CctBackendFactoryTest {
+  @Test
+  public void mergeStrings_whenPartsAreUnequalLength() {
+    String part1 = "hts/eapecm";
+    String part2 = "tp:/xml.o";
+    assertThat(CctBackendFactory.mergeStrings(part1, part2)).isEqualTo("https://example.com");
+  }
+
+  @Test
+  public void mergeStrings_whenPartsAreEqualLength() {
+    String part1 = "hts/eape.o";
+    String part2 = "tp:/xmlscm";
+    assertThat(CctBackendFactory.mergeStrings(part1, part2)).isEqualTo("https://examples.com");
+  }
+
+  @Test
+  public void mergeStrings_whenPart2IsLongerThanPart1() {
+    String part1 = "135";
+    String part2 = "2467";
+    assertThrows(
+        IllegalArgumentException.class, () -> CctBackendFactory.mergeStrings(part1, part2));
+  }
+}

transport/transport-backend-cct/src/test/java/com/google/android/datatransport/cct/GoogleTransportBackendTest.java renamed to transport/transport-backend-cct/src/test/java/com/google/android/datatransport/cct/CctTransportBackendTest.java

@@ -26,22 +26,22 @@
 import com.github.tomakehurst.wiremock.junit.WireMockRule;
 import com.google.android.datatransport.Priority;
 import com.google.android.datatransport.cct.proto.LogResponse;
-import com.google.android.datatransport.runtime.BackendRequest;
-import com.google.android.datatransport.runtime.BackendResponse;
-import com.google.android.datatransport.runtime.BackendResponse.Status;
 import com.google.android.datatransport.runtime.EventInternal;
+import com.google.android.datatransport.runtime.backends.BackendRequest;
+import com.google.android.datatransport.runtime.backends.BackendResponse;
+import com.google.android.datatransport.runtime.backends.BackendResponse.Status;
 import java.util.Collections;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.robolectric.RobolectricTestRunner;
 
 @RunWith(RobolectricTestRunner.class)
-public class GoogleTransportBackendTest {
+public class CctTransportBackendTest {
 
   private static String TEST_ENDPOINT = "http://localhost:8999/api";
-  private static GoogleTransportBackend BACKEND =
-      new GoogleTransportBackend(TEST_ENDPOINT, () -> 3, () -> 1);
+  private static CctTransportBackend BACKEND =
+      new CctTransportBackend(TEST_ENDPOINT, () -> 3, () -> 1);
   private static String TRANSPORT_NAME = "3";
 
   @Rule public WireMockRule wireMockRule = new WireMockRule(8999);

transport/transport-backend-cct/transport-backend-cct.gradle

@@ -76,6 +76,7 @@ dependencies {
     //Android compatible version of Apache httpclient.
     testImplementation 'org.apache.httpcomponents:httpclient-android:4.3.5.1'
     testImplementation 'org.robolectric:robolectric:4.2'
+    testImplementation 'junit:junit:4.13-beta-2'
 
     androidTestImplementation 'com.android.support.test:runner:1.0.2'
     implementation 'com.android.support:support-annotations:28.0.0'

transport/transport-runtime/gradle.properties

@@ -12,4 +12,5 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-version=16.0.0
+version=16.0.0
+android.enableUnitTestBinaryResources=true

transport/transport-runtime/src/main/AndroidManifest.xml

@@ -14,6 +14,12 @@
 
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="com.google.android.datatransport.runtime">
-  <!--Although the *SdkVersion is captured in gradle build files, this is required for non gradle builds-->
-  <!--<uses-sdk android:minSdkVersion="14"/>-->
+    <!--Although the *SdkVersion is captured in gradle build files, this is required for non gradle builds-->
+    <!--<uses-sdk android:minSdkVersion="14"/>-->
+
+    <application>
+        <service
+            android:name=".backends.TransportBackendDiscovery"
+            android:exported="false" />
+    </application>
 </manifest>

transport/transport-runtime/src/main/java/com/google/android/datatransport/runtime/BackendRegistry.java

@@ -39,7 +39,6 @@ public class TransportRuntime implements TransportInternal {
 
   private static volatile TransportRuntimeComponent INSTANCE = null;
 
-  private final BackendRegistry backendRegistry;
   private final Clock eventClock;
   private final Clock uptimeClock;
   private final Scheduler scheduler;
@@ -48,13 +47,11 @@ public class TransportRuntime implements TransportInternal {
 
   @Inject
   TransportRuntime(
-      BackendRegistry backendRegistry,
       @WallTime Clock eventClock,
       @Monotonic Clock uptimeClock,
       Scheduler scheduler,
       SynchronizationGuard guard,
       Uploader uploader) {
-    this.backendRegistry = backendRegistry;
     this.eventClock = eventClock;
     this.uptimeClock = uptimeClock;
     this.scheduler = scheduler;
@@ -92,11 +89,6 @@ public static TransportRuntime getInstance() {
     return localRef.getTransportRuntime();
   }
 
-  /** Register a {@link TransportBackend}. */
-  public void register(String name, TransportBackend backend) {
-    backendRegistry.register(name, backend);
-  }
-
   /** Returns a {@link TransportFactory} for a given {@code backendName}. */
   public TransportFactory newFactory(String backendName) {
     return new TransportFactoryImpl(backendName, this);

transport/transport-runtime/src/main/java/com/google/android/datatransport/runtime/TransportRuntime.java

@@ -16,6 +16,7 @@
 
 import android.content.Context;
 import android.os.Build;
+import com.google.android.datatransport.runtime.backends.BackendRegistry;
 import com.google.android.datatransport.runtime.scheduling.ImmediateScheduler;
 import com.google.android.datatransport.runtime.scheduling.Scheduler;
 import com.google.android.datatransport.runtime.scheduling.jobscheduling.AlarmManagerScheduler;

transport/transport-runtime/src/main/java/com/google/android/datatransport/runtime/TransportRuntimeModule.java

@@ -0,0 +1,20 @@
+// Copyright 2018 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.android.datatransport.runtime.backends;
+
+/** Used by backend discovery to create {@link TransportBackend}s. */
+public interface BackendFactory {
+  TransportBackend create(CreationContext creationContext);
+}