Pushy

A Java library for sending APNs (iOS/OS X) push notifications

Latest release

Pushy v0.8 - August 19, 2016

Older releases can be found at the GitHub project page.

Support

If you have questions about using Pushy, please feel free to join us on the Pushy mailing list. For bug reports and feature requests, please open issues at our GitHub project page. Many common questions are also answered on the Pushy wiki.

Pushy is a Java library for sending APNs (iOS, OS X, and Safari) push notifications. It is written and maintained by the engineers at Turo.

Pushy sends push notifications using Apple’s HTTP/2-based APNs protocol. It distinguishes itself from other push notification libraries with a focus on thorough documentation, asynchronous operation, and design for industrial-scale operation; with Pushy, it’s easy and efficient to maintain multiple parallel connections to the APNs gateway to send large numbers of notifications to many different applications (“topics”).

We believe that Pushy is already the best tool for sending APNs push notifications from Java applications, and we hope you’ll help us make it even better via bug reports and pull requests. If you have questions about using Pushy, please join us on the Pushy mailing list or take a look at the wiki. Thanks!

Getting Pushy

If you use Maven, you can add Pushy to your project by adding the following dependency declaration to your POM:

<dependency>
    <groupId>com.relayrides</groupId>
    <artifactId>pushy</artifactId>
    <version>0.8</version>
</dependency>

If you don’t use Maven (or something else that understands Maven dependencies, like Gradle), you can download Pushy as a .jar file and add it to your project directly. You’ll also need to make sure you have Pushy’s runtime dependencies on your classpath. They are:

Pushy itself requires Java 7 or newer to build and run.

Sending push notifications

Before you can get started with Pushy, you’ll need to do some provisioning work with Apple to register your app and get the required certificates. For details on this process, please see the Provisioning and Development section of Apple’s official documentation. Please note that there are some caveats, particularly under Mac OS X 10.11 (El Capitan).

Once you’ve registered your app and have the requisite certificates, the first thing you’ll need to do to start sending push notifications with Pushy is to create an ApnsClient. Clients need a certificate and private key to authenticate with the APNs server. The most common way to store the certificate and key is in a password-protected PKCS#12 file (you’ll wind up with a password-protected .p12 file if you follow Apple’s instructions at the time of this writing):

final ApnsClient apnsClient = new ApnsClientBuilder()
        .setClientCredentials(new File("/path/to/certificate.p12"), "p12-file-password")
        .build();

Once you’ve created a client, you can connect it to the APNs gateway. Note that this process is asynchronous; the client will return a Future right away, but you’ll need to wait for it to complete before you can send any notifications. Note that this is a Netty Future, which is an extension of the Java Future interface that allows callers to add listeners and adds methods for checking the status of the Future.

final Future<Void> connectFuture = apnsClient.connect(ApnsClient.DEVELOPMENT_APNS_HOST);
connectFuture.await();

Once the client has finished connecting to the APNs server, you can begin sending push notifications. At a minimum, push notifications need a destination token, a topic, and a payload.

final SimpleApnsPushNotification pushNotification;

{
    final ApnsPayloadBuilder payloadBuilder = new ApnsPayloadBuilder();
    payloadBuilder.setAlertBody("Example!");

    final String payload = payloadBuilder.buildWithDefaultMaximumLength();
    final String token = TokenUtil.sanitizeTokenString("<efc7492 bdbd8209>");

    pushNotification = new SimpleApnsPushNotification(token, "com.example.myApp", payload);
}

Like connecting, sending notifications is an asynchronous process. You’ll get a Future immediately, but will need to wait for the Future to complete before you’ll know whether the notification was accepted or rejected by the APNs gateway.

final Future<PushNotificationResponse<SimpleApnsPushNotification>> sendNotificationFuture =
        apnsClient.sendNotification(pushNotification);

The Future will complete in one of three circumstances:

  1. The gateway accepts the notification and will attempt to deliver it to the destination device.
  2. The gateway rejects the notification; this should be considered a permanent failure, and the notification should not be sent again. Additionally, the APNs gateway may indicate a timestamp at which the destination token became invalid. If that happens, you should stop trying to send any notification to that token unless the token has been re-registered since that timestamp.
  3. The Future fails with an exception. This should generally be considered a temporary failure, and callers should try to send the notification again when the problem has been resolved. In particular, the Future may fail with a ClientNotConnectedException, in which case callers may wait for the connection to be restored automatically by waiting for the Future returned by ApnsClient#getReconnectionFuture().

An example:

try {
    final PushNotificationResponse<SimpleApnsPushNotification> pushNotificationResponse =
            sendNotificationFuture.get();

    if (pushNotificationResponse.isAccepted()) {
        System.out.println("Push notification accepted by APNs gateway.");
    } else {
        System.out.println("Notification rejected by the APNs gateway: " +
                pushNotificationResponse.getRejectionReason());

        if (pushNotificationResponse.getTokenInvalidationTimestamp() != null) {
            System.out.println("\t…and the token is invalid as of " +
                pushNotificationResponse.getTokenInvalidationTimestamp());
        }
    }
} catch (final ExecutionException e) {
    System.err.println("Failed to send push notification.");
    e.printStackTrace();

    if (e.getCause() instanceof ClientNotConnectedException) {
        System.out.println("Waiting for client to reconnect…");
        apnsClient.getReconnectionFuture().await();
        System.out.println("Reconnected.");
    }
}

Again, it’s important to note that the returned Future supports listeners; waiting for each individual push notification is inefficient in practice, and most users will be better serverd by adding a listener to the Future instead of blocking until it completes.

Finally, when your application is shutting down, you’ll want to disconnect any active clients:

final Future<Void> disconnectFuture = apnsClient.disconnect();
disconnectFuture.await();

When shutting down, clients will wait for all sent-but-not-acknowledged notifications to receive a reply from the server. Notifications that have been passed to sendNotification but not yet sent to the server (i.e. notifications waiting in an internal queue) will fail immediately when disconnecting. Callers should generally make sure that all sent notifications have been acknowledged by the server before shutting down.

System requirements

Pushy works with Java 7 and newer, but has some additional dependencies depending on the environment in which it is running.

The APNs protocol is built on top of the HTTP/2 protocol. HTTP/2 is a relatively new protocol, and relies on some new developments that aren’t yet wide-spread in the Java world. In particular:

  1. HTTP/2 depends on ALPN, a TLS extension for protocol negotiation. No version of Java has native ALPN support at this time. The ALPN requirement may be met either by using a native SSL provider or by using Jetty’s ALPN implementation under Java 7 or 8.
  2. The HTTP/2 specification requires the use of ciphers that weren’t introduced in Java until Java 8. Using a native SSL provider is the best way to meet this requirement under Java 7. A native SSL provider isn’t a requirement under Java 8, but may still yield performance gains.

Generally speaking, a native SSL provider is the best way to fulfill the system requirements imposed by HTTP/2 because installation is fairly straightforward, it works for Java 7 onward and generally offers better SSL performance than the JDK SSL provider.

Using a native SSL provider

Using a native SSL provider (like OpenSSL, BoringSSL, or LibreSSL) via netty-tcnative fulfills the ALPN and cipher suite requirements imposed by HTTP/2 under all supported versions of Java. To use a native SSL provider, you’ll need to add netty-tcnative as a dependency to your project. The netty-tcnative wiki provides detailed instructions, but in short, you’ll need to add one additional platform-specific dependency to your project; we recommend using a statically-linked “uber jar” flavor for supported operating systems/CPU architectures (currently linux-x86_64, osx-x86_64, and windows-x86_64). This approach will meet all requirements imposed by HTTP/2 under Java 7 and 8.

To add the netty-tcnative uber-jar, you’ll just need to add the following dependency (if you’re using Maven):

<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-tcnative-boringssl-static</artifactId>
    <version>1.1.33.Fork19</version>
</dependency>

Otherwise, you may add the jar to your classpath by the means of your choice.

Please note that Pushy requires netty-tcnative 1.1.33.Fork19 or newer. Additionally, you’ll need alpn-api as a runtime dependency for your project. If you’re managing dependencies manually, you’ll just need to make sure the latest version of alpn-api is available on your classpath.

Using Jetty’s ALPN implementation

As an alternative to a native SSL provider, Jetty’s ALPN implementation. Please note that if you’re not using Oracle JDK 8 or newer (or if you’re using a JDK other than Oracle’s), you’ll need to meet the cipher suite requirement separately; you may do so either by using a native SSL provider (which also fulfills the ALPN requirement) or by using another cryptography provider (which is beyond the scope of this document).

Using Jetty’s ALPN implementation is somewhat more complicated than using a native SSL provider. You’ll need to choose a version of alpn-boot specific to the version (down to the update!) of the JDK you’re using, and then add it to your boot class path (note that this is not the same as your regular classpath). Detailed instructions are provided by Jetty. If you choose to use the alpn-boot approach instead of a native SSL provider, we strongly recommend using jetty-alpn-agent, which will automatically choose the correct version of alpn-boot for your JRE.

Metrics

Pushy includes an interface for monitoring metrics that provide insight into clients’ behavior and performance. You can write your own implementation of the ApnsClientMetricsListener interface to record and report metrics. We also provide a metrics listener that uses the Dropwizard Metrics library as a separate module. To begin receiving metrics, set a listener when building a new client:

final ApnsClient apnsClient = new ApnsClientBuilder()
        .setClientCredentials(new File("/path/to/certificate.p12"), "p12-file-password")
        .setMetricsListener(new MyCustomMetricsListener())
        .build();

Please note that the metric-handling methods in your listener implementation should never call blocking code. It’s appropriate to increment counters directly in the handler methods, but calls to databases or remote monitoring endpoints should be dispatched to separate threads.

Using a proxy

If you need to use a proxy for outbound connections, you may specify a ProxyHandlerFactory when building your ApnsClient instance. Concrete implementations of ProxyHandlerFactory are provided for HTTP, SOCKS4, and SOCKS5 proxies.

An example:

final ApnsClient apnsClient = new ApnsClientBuilder()
        .setClientCredentials(new File("/path/to/certificate.p12"), "p12-file-password")
        .setProxyHandlerFactory(new Socks5ProxyHandlerFactory(
            new InetSocketAddress("my.proxy.com", 1080), "username", "password"))
        .build();

final Future<Void> connectFuture = apnsClient.connect(ApnsClient.DEVELOPMENT_APNS_HOST);
connectFuture.await();

Logging

Pushy uses SLF4J for logging. If you’re not already familiar with it, SLF4J is a facade that allows users to choose which logging library to use at deploy time by adding a specific “binding” to the classpath. To avoid making the choice for you, Pushy itself does not depend on any SLF4J bindings; you’ll need to add one on your own (either by adding it as a dependency in your own project or by installing it directly). If you have no SLF4J bindings on your classpath, you’ll probably see a warning that looks something like this:

SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.

For more information, see the SLF4J user manual.

Pushy uses logging levels as follows:

Level Events logged
error Serious, unrecoverable errors; recoverable errors that likely indicate a bug in Pushy
warn Serious, but recoverable errors; errors that may indicate a bug in caller’s code
info Important lifecycle events
debug Minor lifecycle events; expected exceptions
trace Individual IO operations

Using Pushy in an application container

If you plan to use Pushy inside an application container (like Tomcat), you may have to take some additional steps and should be aware of some limitations detailed on the “Using Pushy in an application continer” wiki page.

License and status

Pushy is available under the MIT License.

The current version of Pushy is 0.8. We consider it to be fully functional (and use it in production!), but the public API may change significantly before a 1.0 release.