Fail Firestore client if we can't establish SSL connection

firebase-firestore/CHANGELOG.md

@@ -1,4 +1,8 @@
 # Unreleased
+- [changed] Instead of failing silently, Firestore now crashes the client app
+  if it fails to load SSL Ciphers. To avoid these crashes, you must bundle 
+  Conscrypt to support non-GMSCore devices on Android KitKat or JellyBean (see
+  https://github.com/grpc/grpc-java/blob/master/SECURITY.md#tls-on-android).
 
 # 20.1.0
 - [changed] SSL and gRPC initialization now happens on a separate thread, which

firebase-firestore/src/main/java/com/google/firebase/firestore/remote/AbstractStream.java

@@ -14,6 +14,7 @@
 
 package com.google.firebase.firestore.remote;
 
+import static com.google.firebase.firestore.remote.Datastore.SSL_DEPENDENCY_ERROR_MESSAGE;
 import static com.google.firebase.firestore.util.Assert.hardAssert;
 
 import androidx.annotation.Nullable;
@@ -24,6 +25,7 @@
 import com.google.firebase.firestore.util.AsyncQueue.TimerId;
 import com.google.firebase.firestore.util.ExponentialBackoff;
 import com.google.firebase.firestore.util.Logger;
+import com.google.firebase.firestore.util.Util;
 import io.grpc.ClientCall;
 import io.grpc.Metadata;
 import io.grpc.MethodDescriptor;
@@ -269,6 +271,13 @@ private void close(State finalState, Status status) {
         "Can't provide an error when not in an error state.");
     workerQueue.verifyIsCurrentThread();
 
+    if (Datastore.isSslHandshakeError(status)) {
+      // The Android device is missing required SSL Ciphers. This error is non-recoverable and must
+      // be addressed by the app developer (see https://bit.ly/2XFpdma).
+      Util.crashMainThread(
+          new IllegalStateException(SSL_DEPENDENCY_ERROR_MESSAGE, status.getCause()));
+    }
+
     // Cancel any outstanding timers (they're guaranteed not to execute).
     cancelIdleCheck();
     this.backoff.cancel();

firebase-firestore/src/main/java/com/google/firebase/firestore/remote/Datastore.java

@@ -15,6 +15,7 @@
 package com.google.firebase.firestore.remote;
 
 import android.content.Context;
+import android.os.Build;
 import com.google.android.gms.tasks.Task;
 import com.google.firebase.firestore.FirebaseFirestoreException;
 import com.google.firebase.firestore.auth.CredentialsProvider;
@@ -31,13 +32,15 @@
 import com.google.firestore.v1.CommitResponse;
 import com.google.firestore.v1.FirestoreGrpc;
 import io.grpc.Status;
+import java.net.ConnectException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import javax.net.ssl.SSLHandshakeException;
 
 /**
  * Datastore represents a proxy for the remote server, hiding details of the RPC layer. It:
@@ -54,6 +57,16 @@
  */
 public class Datastore {
 
+  /**
+   * Error message to surface when Firestore fails to establish an SSL connection. A failed SSL
+   * connection likely indicates that the developer needs to provide an updated OpenSSL stack as
+   * part of their app's dependencies.
+   */
+  static final String SSL_DEPENDENCY_ERROR_MESSAGE =
+      "The Firestore SDK failed to establish a secure connection. This is likely a problem with "
+          + "your app, rather than with Firestore itself. See https://bit.ly/2XFpdma for "
+          + "instructions on how to enable TLS on Android 4.x devices.";
+
   /** Set of lowercase, white-listed headers for logging purposes. */
   static final Set<String> WHITE_LISTED_HEADERS =
       new HashSet<>(
@@ -208,6 +221,22 @@ public static boolean isPermanentError(Status status) {
     }
   }
 
+  /**
+   * Determine whether the given status maps to the error that GRPC-Java throws when an Android
+   * device is missing required SSL Ciphers.
+   *
+   * <p>This error is non-recoverable and must be addressed by the app developer.
+   */
+  public static boolean isSslHandshakeError(Status status) {
+    Status.Code code = status.getCode();
+    Throwable t = status.getCause();
+
+    return Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP
+        && code.equals(Status.Code.UNAVAILABLE)
+        && (t instanceof SSLHandshakeException
+            || (t instanceof ConnectException && t.getMessage().contains("EHOSTUNREACH")));
+  }
+
   /**
    * Determines whether the given status has an error code that represents a permanent error when
    * received in response to a write operation.

firebase-firestore/src/main/java/com/google/firebase/firestore/remote/FirestoreChannel.java

@@ -199,7 +199,7 @@ public void onClose(Status status, Metadata trailers) {
                       if (status.isOk()) {
                         tcs.setResult(results);
                       } else {
-                        tcs.setException(Util.exceptionFromStatus(status));
+                        tcs.setException(exceptionFromStatus(status));
                       }
                     }
                   },
@@ -244,7 +244,7 @@ public void onClose(Status status, Metadata trailers) {
                                   Code.INTERNAL));
                         }
                       } else {
-                        tcs.setException(Util.exceptionFromStatus(status));
+                        tcs.setException(exceptionFromStatus(status));
                       }
                     }
                   },
@@ -262,6 +262,17 @@ public void onClose(Status status, Metadata trailers) {
     return tcs.getTask();
   }
 
+  private FirebaseFirestoreException exceptionFromStatus(Status status) {
+    if (Datastore.isSslHandshakeError(status)) {
+      return new FirebaseFirestoreException(
+          Datastore.SSL_DEPENDENCY_ERROR_MESSAGE,
+          Code.fromValue(status.getCode().value()),
+          status.getCause());
+    }
+
+    return Util.exceptionFromStatus(status);
+  }
+
   public void invalidateToken() {
     credentialsProvider.invalidateToken();
   }

firebase-firestore/src/main/java/com/google/firebase/firestore/util/Util.java

@@ -14,6 +14,8 @@
 
 package com.google.firebase.firestore.util;
 
+import android.os.Handler;
+import android.os.Looper;
 import androidx.annotation.Nullable;
 import com.google.android.gms.tasks.Continuation;
 import com.google.cloud.datastore.core.number.NumberComparisonHelper;
@@ -211,4 +213,13 @@ public static String toDebugString(ByteString bytes) {
   public static String typeName(@Nullable Object obj) {
     return obj == null ? "null" : obj.getClass().getName();
   }
+
+  /** Raises an exception on Android's UI Thread and crashes the end user's app. */
+  public static void crashMainThread(RuntimeException exception) {
+    new Handler(Looper.getMainLooper())
+        .post(
+            () -> {
+              throw exception;
+            });
+  }
 }