How to write an Apple Push Notification Provider in C#?

Question

Apple really had bad documentation about how the provider connects and communicates to their service (at the time of writing - 2009). I am confused about the protocol. How is this done in C#?

Answer 1

Working code example:

int port = 2195;
String hostname = "gateway.sandbox.push.apple.com";

//load certificate
string certificatePath = @"cert.p12";
string certificatePassword = "";
X509Certificate2 clientCertificate = new X509Certificate2(certificatePath, certificatePassword);
X509Certificate2Collection certificatesCollection = new X509Certificate2Collection(clientCertificate);

TcpClient client = new TcpClient(hostname, port);
SslStream sslStream = new SslStream(
        client.GetStream(),
        false,
        new RemoteCertificateValidationCallback(ValidateServerCertificate),
        null
);

try
{
    sslStream.AuthenticateAsClient(hostname, certificatesCollection, SslProtocols.Tls, true);
}
catch (AuthenticationException ex)
{
    client.Close();
    return;
}

// Encode a test message into a byte array.
MemoryStream memoryStream = new MemoryStream();
BinaryWriter writer = new BinaryWriter(memoryStream);

writer.Write((byte)0);  //The command
writer.Write((byte)0);  //The first byte of the deviceId length (big-endian first byte)
writer.Write((byte)32); //The deviceId length (big-endian second byte)

String deviceId = "DEVICEIDGOESHERE";
writer.Write(ToByteArray(deviceId.ToUpper()));

String payload = "{\"aps\":{\"alert\":\"I like spoons also\",\"badge\":14}}";

writer.Write((byte)0); //First byte of payload length; (big-endian first byte)
writer.Write((byte)payload.Length); //payload length (big-endian second byte)

byte[] b1 = System.Text.Encoding.UTF8.GetBytes(payload);
writer.Write(b1);
writer.Flush();

byte[] array = memoryStream.ToArray();
sslStream.Write(array);
sslStream.Flush();

// Close the client connection.
client.Close();

Answer 2

I hope this is relevant (slightly), but I have just successfully created one for Java, so conceptually quite similar to C# (except perhaps the SSL stuff, but that shouldn't be too hard to modify. Below is a sample message payload and crypto setup:

    int port = 2195;
    String hostname = "gateway.sandbox.push.apple.com";


    char []passwKey = "<keystorePassword>".toCharArray();
    KeyStore ts = KeyStore.getInstance("PKCS12");
    ts.load(new FileInputStream("/path/to/apn_keystore/cert.p12"), passwKey);

    KeyManagerFactory tmf = KeyManagerFactory.getInstance("SunX509");
    tmf.init(ts,passwKey);
    SSLContext sslContext = SSLContext.getInstance("TLS");
    sslContext.init(tmf.getKeyManagers(), null, null);
    SSLSocketFactory factory =sslContext.getSocketFactory();
    SSLSocket socket = (SSLSocket) factory.createSocket(hostname,port); // Create the ServerSocket
    String[] suites = socket.getSupportedCipherSuites();
    socket.setEnabledCipherSuites(suites);
    //start handshake

    socket.startHandshake();


    // Create streams to securely send and receive data to the server
    InputStream in = socket.getInputStream();
    OutputStream out = socket.getOutputStream();



    // Read from in and write to out...
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    baos.write(0); //The command
    System.out.println("First byte Current size: " + baos.size());

    baos.write(0); //The first byte of the deviceId length    
    baos.write(32); //The deviceId length

    System.out.println("Second byte Current size: " + baos.size());

    String deviceId = "<heaxdecimal representation of deviceId";
    baos.write(hexStringToByteArray(deviceId.toUpperCase()));
    System.out.println("Device ID: Current size: " + baos.size());


    String payload = "{\"aps\":{\"alert\":\"I like spoons also\",\"badge\":14}}";
    System.out.println("Sending payload: " + payload);
    baos.write(0); //First byte of payload length;
    baos.write(payload.length());
    baos.write(payload.getBytes());

    out.write(baos.toByteArray());
    out.flush();

    System.out.println("Closing socket..");
    // Close the socket
    in.close();
    out.close();

}

Once again, not C#, but at least closer than the poor ObjC sample that Apple provides.