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Jetty/Feature/NPN



Introduction

The Jetty project provides an implementation of the Next Protocol Negotiation TLS Extension (NPN) for OpenJDK 7 or greater.

Jetty's NPN implementation, although hosted under the umbrella of the Jetty project, is independent of Jetty (the Servlet Container), and can be reused in any other Java network server.

Feature

JVM Startup Usage

In order to enable NPN support, you need to start the JVM with:

java -Xbootclasspath/p:<path_to_npn_boot_jar> ...

where path_to_npn_boot_jar is the path on file system for the NPN Boot jar file, for example one at the following Maven coordinates org.mortbay.jetty.npn:npn-boot.

API Usage

Applications needs to interact with the negotiation of the next protocol performed by the NPN TLS extension. For example, server applications need to know whether the client supports NPN, and client applications needs to know the list of protocols supported by the server, and so on.

In order to provide this interaction, Jetty's NPN implementation provides an API to applications, hosted at Maven coordinates org.eclipse.jetty.npn:npn-api. This dependency needs to be declared as "provided", because it is already included in the npn-boot jar (see section above) and therefore will be available in the boot classpath.

The API is composed of a single class, org.eclipse.jetty.npn.NextProtoNego, and applications need to register instances of SSLSocket or SSLEngine with a ClientProvider or ServerProvider (depending on whether the application is a client or server application). Refer to NextProtoNego javadocs and to the examples below for further details about client and server provider methods.

Client Example

SSLContext sslContext = ...;
SSLSocket sslSocket = (SSLSocket)context.getSocketFactory()
        .createSocket("localhost", server.getLocalPort());
 
NextProtoNego.put(sslSocket, new NextProtoNego.ClientProvider()
{
    @Override
    public boolean supports()
    {
        return true;
    }
 
    @Override
    public void unsupported()
    {
    }
 
    @Override
    public String selectProtocol(List<String> protocols)
    {
        return protocols.get(0);
    }
});

The NextProtoNego.ClientProvider methods supports(), unsupported() and selectProtocol(List<String>) will be called by the NPN implementation, so that the client application can, respectively, decide whether to support NPN, whether the server supports NPN, and select one of the protocols supported by the server.

The example for SSLEngine is identical, and you just need to replace the SSLSocket instance with a SSLEngine instance.

Server Example

SSLSocket sslSocket = ...;
NextProtoNego.put(sslSocket, new NextProtoNego.ServerProvider()
{
    @Override
    public void unsupported()
    {
    }
 
    @Override
    public List<String> protocols()
    {
        return Arrays.asList("http/1.1");
    }
 
    @Override
    public void protocolSelected(String protocol)
    {
        System.out.println("Protocol Selected is: " + protocol);
    }
});

The NextProtoNego.ServerProvider methods unsupported(), protocols() and protocolSelected(String) will be called by the NPN implementation, so that the server application can, respectively, know whether the client supports NPN, provide the list of protocols supported by the server, and know what is the protocol chosen by the client.

Implementation Details

The NPN implementation relies on modification of few OpenJDK classes and on few new classes that needs to live in the sun.security.ssl package. These classes are released under the same GPLv2+exception license of OpenJDK.

The NextProtoNego class is released under same license as the classes of the Jetty project.

Usage in Unit Tests

It is possible to write and run unit tests that make use of the NPN implementation. The solution that we used with Maven is to specify an additional command line argument to the Surefire plugin:

<project ...>
 
  <properties>
    <npn-version>7.6.2.v20120308</npn-version>
  </properties>
 
  <build>
    <plugins>
      <plugin>
        <artifactId>maven-surefire-plugin</artifactId>
        <configuration>
          <argLine>-Xbootclasspath/p:${settings.localRepository}/org/mortbay/jetty/npn/npn-boot/${npn-version}/npn-boot-${npn-version}.jar</argLine>
        </configuration>
      </plugin>
 
      ...
 
    </plugins>
  </build>
 
  ...
 
</project>