gRPC Cronet Transport

EXPERIMENTAL: gRPC's Cronet transport is an experimental API, and is not yet integrated with our build system. Using Cronet with gRPC requires manually integrating the Cronet libraries and the gRPC code in this directory into your Android application.

This code enables using the Chromium networking stack (Cronet) as the transport layer for gRPC on Android. This lets your Android app make RPCs using the same networking stack as used in the Chrome browser.

Some advantages of using Cronet with gRPC:

• Bundles an OpenSSL implementation, enabling TLS connections even on older versions of Android without additional configuration
• Robust to Android network connectivity changes
• Support for QUIC

Cronet jars are not currently available on Maven. The instructions at https://github.com/GoogleChrome/cronet-sample/blob/master/README.md describe how to manually download the Cronet binaries and add them to your Android application. You will also need to copy the gRPC source files contained in this directory into your application's code, as we do not currently provide a grpc-cronet dependency.

To use Cronet, you must have the ACCESS_NETWORK_STATE permission set in AndroidManifest.xml:

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

Once the above steps are completed, you can create a gRPC Cronet channel as follows:

import io.grpc.cronet.CronetChannelBuilder;
import org.chromium.net.ExperimentalCronetEngine;

...

ExperimentalCronetEngine engine =
    new ExperimentalCronetEngine.Builder(context /* Android Context */).build();
ManagedChannel channel = CronetChannelBuilder.forAddress("localhost", 8080, engine).build();