Added precondition format checks for App-Id and Api-Key (firebase#1470)

* Added precondition format checks for App-Id and Api-Key

* Make Firebase Project id/number mandatory. GCM sender ID can no longer replace it.

* code formatting

Author: ChaoqunCHEN

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

@@ -146,14 +146,22 @@ private void preConditionChecks() {
     Preconditions.checkNotEmpty(getApplicationId());
     Preconditions.checkNotEmpty(getProjectIdentifier());
     Preconditions.checkNotEmpty(getApiKey());
+    Preconditions.checkArgument(
+        Utils.isValidAppIdFormat(getApplicationId()),
+        "Please set your Application ID. A valid Firebase App ID is required to communicate "
+            + "with Firebase server APIs: It identifies your application with Firebase."
+            + "Please refer to https://firebase.google.com/support/privacy/init-options.");
+    Preconditions.checkArgument(
+        Utils.isValidApiKeyFormat(getApiKey()),
+        "Please set a valid API key. A Firebase API key is required to communicate with "
+            + "Firebase server APIs: It authenticates your project with Google."
+            + "Please refer to https://firebase.google.com/support/privacy/init-options.");
   }
 
   /** Returns the Project Id or Project Number for the Firebase Project. */
   @Nullable
   String getProjectIdentifier() {
-    return TextUtils.isEmpty(firebaseApp.getOptions().getProjectId())
-        ? firebaseApp.getOptions().getGcmSenderId()
-        : firebaseApp.getOptions().getProjectId();
+    return firebaseApp.getOptions().getProjectId();
   }
 
   /**

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

@@ -15,12 +15,16 @@
 package com.google.firebase.installations;
 
 import android.text.TextUtils;
+import androidx.annotation.Nullable;
 import com.google.firebase.installations.local.PersistedInstallationEntry;
 import java.util.concurrent.TimeUnit;
+import java.util.regex.Pattern;
 
 /** Util methods used for {@link FirebaseInstallations} */
 class Utils {
   public static final long AUTH_TOKEN_EXPIRATION_BUFFER_IN_SECS = TimeUnit.HOURS.toSeconds(1);
+  private static final String APP_ID_IDENTIFICATION_SUBSTRING = ":";
+  private static final Pattern API_KEY_FORMAT = Pattern.compile("\\AA[\\w-]{38}\\z");
 
   /**
    * Checks if the FIS Auth token is expired or going to expire in next 1 hour {@link
@@ -41,4 +45,12 @@ public boolean isAuthTokenExpired(PersistedInstallationEntry entry) {
   public long currentTimeInSecs() {
     return TimeUnit.MILLISECONDS.toSeconds(System.currentTimeMillis());
   }
+
+  static boolean isValidAppIdFormat(@Nullable String appId) {
+    return appId.contains(APP_ID_IDENTIFICATION_SUBSTRING);
+  }
+
+  static boolean isValidApiKeyFormat(@Nullable String apiKey) {
+    return API_KEY_FORMAT.matcher(apiKey).matches();
+  }
 }