FIS getAuthToken implementation.

firebase-installations-interop/src/main/java/com/google/firebase/installations/FirebaseInstallationsApi.java

@@ -31,7 +31,7 @@ public interface FirebaseInstallationsApi {
   Task<String> getId();
 
   /** Async function that returns a auth token(public key) of this Firebase app installation. */
-  Task<InstallationTokenResult> getAuthToken(boolean forceRefresh);
+  Task<String> getAuthToken(boolean forceRefresh);
 
   /**
    * Async function that deletes this Firebase app installation from Firebase backend. This call

firebase-installations/src/androidTest/java/com/google/firebase/installations/FirebaseInstallationsInstrumentedTest.java

@@ -38,6 +38,7 @@
 import com.google.firebase.installations.remote.FirebaseInstallationServiceClient;
 import com.google.firebase.installations.remote.FirebaseInstallationServiceException;
 import com.google.firebase.installations.remote.InstallationResponse;
+import com.google.firebase.installations.remote.InstallationTokenResult;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.SynchronousQueue;

firebase-installations/src/main/java/com/google/firebase/installations/FirebaseInstallations.java

@@ -29,6 +29,7 @@
 import com.google.firebase.installations.remote.FirebaseInstallationServiceClient;
 import com.google.firebase.installations.remote.FirebaseInstallationServiceException;
 import com.google.firebase.installations.remote.InstallationResponse;
+import com.google.firebase.installations.remote.InstallationTokenResult;
 import java.util.concurrent.Executor;
 import java.util.concurrent.SynchronousQueue;
 import java.util.concurrent.ThreadPoolExecutor;
@@ -54,6 +55,8 @@ public class FirebaseInstallations implements FirebaseInstallationsApi {
   private final Clock clock;
   private final Utils utils;
 
+  private static final long TOKEN_EXPIRATION_BUFFER = 3600L;
+
   /** package private constructor. */
   FirebaseInstallations(FirebaseApp firebaseApp) {
     this(
@@ -115,11 +118,17 @@ public Task<String> getId() {
         .onSuccessTask(this::registerFidIfNecessary);
   }
 
-  /** Returns a auth token(public key) of this Firebase app installation. */
+  /**
+   * Returns a valid authentication token for the Firebase installation. Generates a new token if
+   * one doesn't exist, is expired or about to expire.
+   *
+   * <p>Should only be called if the Firebase Installation is registered.
+   */
   @NonNull
   @Override
-  public Task<InstallationTokenResult> getAuthToken(boolean forceRefresh) {
-    return Tasks.forResult(InstallationTokenResult.builder().build());
+  public Task<String> getAuthToken(final boolean forceRefresh) {
+    return Tasks.call(executor, this::getId)
+        .continueWith(call(() -> refreshAuthTokenIfNecessary(forceRefresh)));
   }
 
   /**
@@ -169,6 +178,16 @@ private static <F, T> Continuation<F, T> orElse(@NonNull Supplier<T> supplier) {
     };
   }
 
+  @NonNull
+  private static <F, T> Continuation<F, T> call(@NonNull Supplier<T> supplier) {
+    return t -> {
+      if (!t.isComplete()) {
+        Tasks.await(t);
+      }
+      return supplier.get();
+    };
+  }
+
   private PersistedFidEntry createAndPersistNewFid() throws FirebaseInstallationsException {
     String fid = utils.createRandomFid();
     persistFid(fid);
@@ -214,7 +233,7 @@ private void updatePersistedFidWithPendingStatus(String fid) {
   private Void registerAndSaveFid(PersistedFidEntry persistedFidEntry)
       throws FirebaseInstallationsException {
     try {
-      long creationTime = TimeUnit.MILLISECONDS.toSeconds(clock.currentTimeMillis());
+      long creationTime = currentTime();
 
       InstallationResponse installationResponse =
           serviceClient.createFirebaseInstallation(
@@ -244,6 +263,79 @@ private Void registerAndSaveFid(PersistedFidEntry persistedFidEntry)
     }
     return null;
   }
+
+  private String refreshAuthTokenIfNecessary(boolean forceRefresh)
+      throws FirebaseInstallationsException {
+
+    PersistedFidEntry persistedFidEntry = persistedFid.readPersistedFidEntryValue();
+
+    if (persistedFidEntry == null) {
+      throw new FirebaseInstallationsException(
+          "Failed to create Firebase Installation.",
+          FirebaseInstallationsException.Status.SDK_INTERNAL_ERROR);
+    }
+
+    return forceRefresh
+        ? fetchAuthTokenFromServer(persistedFidEntry)
+        : getPersistedAuthToken(persistedFidEntry);
+  }
+
+  private String getPersistedAuthToken(PersistedFidEntry persistedFidEntry)
+      throws FirebaseInstallationsException {
+    if (!isPersistedFidRegistered(persistedFidEntry)) {
+      throw new FirebaseInstallationsException(
+          "Firebase Installation is not registered.",
+          FirebaseInstallationsException.Status.SDK_INTERNAL_ERROR);
+    }
+
+    return isAuthTokenExpired(persistedFidEntry)
+        ? fetchAuthTokenFromServer(persistedFidEntry)
+        : persistedFidEntry.getAuthToken();
+  }
+
+  private boolean isPersistedFidRegistered(PersistedFidEntry persistedFidEntry) {
+    return persistedFidEntry != null
+        && persistedFidEntry.getRegistrationStatus() == RegistrationStatus.REGISTERED;
+  }
+
+  /** Calls the FIS servers to generate an auth token for this Firebase installation. */
+  private String fetchAuthTokenFromServer(PersistedFidEntry persistedFidEntry)
+      throws FirebaseInstallationsException {
+    try {
+      long creationTime = currentTime();
+      InstallationTokenResult tokenResult =
+          serviceClient.generateAuthToken(
+              /*apiKey= */ firebaseApp.getOptions().getApiKey(),
+              /*fid= */ persistedFidEntry.getFirebaseInstallationId(),
+              /*projectID= */ firebaseApp.getOptions().getProjectId(),
+              /*refreshToken= */ persistedFidEntry.getRefreshToken());
+
+      persistedFid.insertOrUpdatePersistedFidEntry(
+          PersistedFidEntry.builder()
+              .setFirebaseInstallationId(persistedFidEntry.getFirebaseInstallationId())
+              .setRegistrationStatus(RegistrationStatus.REGISTERED)
+              .setAuthToken(tokenResult.getToken())
+              .setRefreshToken(persistedFidEntry.getRefreshToken())
+              .setExpiresInSecs(tokenResult.getTokenExpirationTimestampMillis())
+              .setTokenCreationEpochInSecs(creationTime)
+              .build());
+
+      return tokenResult.getToken();
+    } catch (FirebaseInstallationServiceException exception) {
+      throw new FirebaseInstallationsException(
+          "Failed to generate auth token for a Firebase Installation.",
+          FirebaseInstallationsException.Status.SDK_INTERNAL_ERROR);
+    }
+  }
+
+  private boolean isAuthTokenExpired(PersistedFidEntry persistedFidEntry) {
+    return (persistedFidEntry.getTokenCreationEpochInSecs() + persistedFidEntry.getExpiresInSecs()
+        < currentTime() + TOKEN_EXPIRATION_BUFFER);
+  }
+
+  private long currentTime() {
+    return TimeUnit.MILLISECONDS.toSeconds(clock.currentTimeMillis());
+  }
 }
 
 interface Supplier<T> {

firebase-installations/src/main/java/com/google/firebase/installations/remote/FirebaseInstallationServiceClient.java

@@ -16,7 +16,6 @@
 
 import android.util.JsonReader;
 import androidx.annotation.NonNull;
-import com.google.firebase.installations.InstallationTokenResult;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.net.URL;

firebase-installations/src/main/java/com/google/firebase/installations/remote/InstallationResponse.java

@@ -16,7 +16,6 @@
 
 import androidx.annotation.NonNull;
 import com.google.auto.value.AutoValue;
-import com.google.firebase.installations.InstallationTokenResult;
 
 @AutoValue
 public abstract class InstallationResponse {

firebase-installations/src/main/java/com/google/firebase/installations/remote/InstallationTokenResult.java

@@ -0,0 +1,54 @@
+// Copyright 2019 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.firebase.installations.remote;
+
+import androidx.annotation.NonNull;
+import com.google.auto.value.AutoValue;
+
+/** This class represents a set of values describing a FIS Auth Token Result. */
+@AutoValue
+public abstract class InstallationTokenResult {
+
+  /** A new FIS Auth-Token, created for this Firebase Installation. */
+  @NonNull
+  public abstract String getToken();
+  /**
+   * The amount of time, in milliseconds, before the auth-token expires for this Firebase
+   * Installation.
+   */
+  @NonNull
+  public abstract long getTokenExpirationTimestampMillis();
+
+  @NonNull
+  public abstract Builder toBuilder();
+
+  /** Returns a default Builder object to create an InstallationResponse object */
+  @NonNull
+  public static InstallationTokenResult.Builder builder() {
+    return new AutoValue_InstallationTokenResult.Builder();
+  }
+
+  @AutoValue.Builder
+  public abstract static class Builder {
+    @NonNull
+    public abstract Builder setToken(@NonNull String value);
+
+    @NonNull
+    public abstract Builder setTokenExpirationTimestampMillis(@NonNull long value);
+
+    @NonNull
+    public abstract InstallationTokenResult build();
+  }
+}