Apache Felix HTTP Service

This is an implementation of the HTTP Whiteboard Service as described in chapter 140 of the OSGi Compendium (R7) in combination with an implementation of the HTTP Service Specification as described in chapter 102 of the OSGi Compendium. The goal is to provide a standard and simplified way to register servlets, listeners, filters, and resources in a servlet container, to managed them in servlet contexts, and to associate them with URIs. Complete set of features:

• Standard OSGi Http Service implementation
• Standard OSGi Http Whiteboard implementation
• Run either with Jetty or inside your own application server using the servlet bridge
• Correctly versioned Servlet API.

Installing

The Apache Felix HTTP Service project includes several bundles.

• org.apache.felix.http.servlet-api - Provides the Servlet API (versions 2.6, 3.0, and 3.1 of the Servlet specification)
• org.apache.felix.http.api - Provides the OSGi APIs for the Http Whiteboard and Http Service.
• org.apache.felix.http.jetty - Implementation that is embedding Jetty server (currently Jetty 9, requiring Java 8). This bundle includes the http.api bundle.
• org.apache.felix.http.sslfilter - Servlet filter for handling SSL termination.
• org.apache.felix.http.bridge - Implementation that uses the host application server (bridged mode). Must be used with the proxy (see below)
• org.apache.felix.http.cometd - Adds Comet/Ajax Push functionality to the HTTP Service implementation.
• org.apache.felix.http.proxy - Proxy that is needed inside WAR when deployed inside an application server.

Note that as of version 3.x, the Servlet APIs are no longer packaged with the implementation bundles! If you are migrating from lower versions, be sure to add the org.apache.felix.http.servlet-api (or any other compatible Serlvet API bundle) to your classpath and deployment!

Installing additional bundles for the optional HTTP/2 support with jetty

The jetty implementation uses the OSGi ServiceLoader mediator technique to find certain pluggable components that are required for HTTP/2 support. Your OSGi runtime must first have the bundles needed for OSGi ServiceLoader support deployed. Background information about the OSGi ServiceLoader integration is discussed here

Deploying the following set of bundles would be one way to enable the ServiceLoader mediator support:

• org.apache.aries.spifly:org.apache.aries.spifly.dynamic.bundle:1.3.0
• org.apache.aries:org.apache.aries.util:1.1.3
• org.ow2.asm:asm:8.0.1
• org.ow2.asm:asm-analysis:8.0.1
• org.ow2.asm:asm-commons:8.0.1
• org.ow2.asm:asm-tree:8.0.1
• org.ow2.asm:asm-util:8.0.1

Next, depending on your server environment you must choose only one of the following sets of additional bundles to deploy as described in the jetty documentation

1. For java 9 or later:

   • org.eclipse.jetty.alpn:alpn-api:1.1.3.v20160715
   • org.eclipse.jetty:jetty-alpn-java-server:${jetty.version}

2. For java 8:

   • org.eclipse.jetty:jetty-alpn-openjdk8-server:${jetty.version}

   • For java 8 versions earlier than 1.8.0_252 download and add -Xbootclasspath/p:/path_to_file_here/alpn-boot-8.1.13.v20181017.jar as an argument to the java process and then deploy the following bundle:

     • org.eclipse.jetty.osgi:jetty-osgi-alpn:${jetty.version}

   • For java 8 version 1.8.0_252 or later skip the bootclasspath argument and deploy the following bundle instead:

     • org.eclipse.jetty.alpn:alpn-api:1.1.3.v20160715

Using the OSGi Http Whiteboard

The OSGi whiteboard implementation simplifies the task of registering servlets, filters, resources, listeners, and servlet contexts. For a complete introduction, please refer to the OSGi R7 Compendium or Enterprise specification.

For a short introduction: Such a whiteboard service can be registered by exporting it as a service, making it no longer necessary to track and use the HttpService directly. The whiteboard implementation detects all javax.servlet.Servlet and javax.servlet.Filter services with the right service properties. Let us illustrate the usage by registering a servlet:

public class Activator implements BundleActivator {
    private ServiceRegistration registration;

    public void start(BundleContext context) throws Exception {
        Hashtable props = new Hashtable();
        props.put("osgi.http.whiteboard.servlet.pattern", "/hello");
        props.put("servlet.init.message", "Hello World!");

        this.registration = context.registerService(Servlet.class.getName(), new HelloWorldServlet(), props);
    }

    public void stop(BundleContext context) throws Exception {
        this.registration.unregister();
    }
}

To ensure the HTTP whiteboard service picks up your servlet and filter correctly, your service registration must provide several service properties.

Servlet service properties

• osgi.http.whiteboard.servlet.pattern - defines the servlet pattern to register the servlet under, should be a path as defined in the Servlet specification.
• osgi.http.whiteboard.context.select - Filter expression to select the servlet context (optional).
• servlet.init.* - these properties (sans the servlet.init. prefix) are made available throught the ServletConfig object of your servlet. This allows you to supply your servlet initialization parameters as you would normally do in the web descriptor (web.xml).

Filter service properties

• osgi.http.whiteboard.filter.regex - The regular expression pattern to register filter with.
• osgi.http.whiteboard.context.select - Filter expression to select the servlet context (optional).
• service.ranking - an integer value that allows you to specify where in the filter chain the filter should be registered. Higher rankings will be placed first in the chain, that is, filter chains are sorted in descending order. If omitted, a ranking of zero (0) is used.
• filter.init.* - these properties (sans the filter.init. prefix) are made available throught the FilterConfig object of your filter. This allows you to supply your filter initialization parameters as you would normally do in the web descriptor (web.xml).

ServletContextHelper service properties

• osgi.http.whiteboard.context.name - the identifier of the registered HTTP context to be referenced by a servlet or filter service
• osgi.http.whiteboard.context.path - The path of the servlet context.

Using the HttpService

In general the Http Service is regarded legacy and the OSGi Http Whiteboard should be used instead. If you still want to use the Http Service, this is a brief introduction. The main components provided by the Apache Felix HTTP Service bundle are:

• HttpService - Service used to dynamically register resources and servlets;
• HttpContext - Additional (optional) component to handle authentication, resource and mime type mappings.

Servlets created for the OSGi HTTP service don't need to have any reference to the OSGi specification (they only need to conform to the Servlet specification), like in the example:

public class HelloWorld extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("Hello World");		
    }
}

To register a servlet and map it to a URI, you need to retrieve the HttpService and call its registerServlet method. For this example, a ServiceTracker is used to ensure that the registration occurs when a HttpService actually is available, and a deregistration occurs when the HttpService becomes unavailable. Alternatively, you can use more high-level dependency management libraries, like Declarative Services, Felix Dependency Manager, or Felix HTTP whiteboard service (see below).

public class Activator implements BundleActivator {
    private ServiceTracker httpTracker;

    public void start(BundleContext context) throws Exception {
        httpTracker = new ServiceTracker(context, HttpService.class.getName(), null) {
          public void removedService(ServiceReference reference, Object service) {
            // HTTP service is no longer available, unregister our servlet...
            try {
               ((HttpService) service).unregister("/hello");
            } catch (IllegalArgumentException exception) {
               // Ignore; servlet registration probably failed earlier on...
            }
          }

          public Object addingService(ServiceReference reference) {
            // HTTP service is available, register our servlet...
            HttpService httpService = (HttpService) this.context.getService(reference);
            try {
              httpService.registerServlet("/hello", new HelloWorld(), null, null);
            } catch (Exception exception) {
              exception.printStackTrace();
            }
            return httpService;
          }
        };
        // start tracking all HTTP services...
        httpTracker.open();
    }

    public void stop(BundleContext context) throws Exception {
        // stop tracking all HTTP services...
        httpTracker.close();
    }
}

In the same way, you can unregister a servlet (for instance, in the removedMethod method in the former example) by calling the HttpService.unregister method.

As you notice in the example above, the registerServlet method accepts four parameters:

• the servlet alias;
• the Servlet instance;
• an additional configuration Dictionary;
• a HttpContext.

The servlet alias must begin with a slash and must not end with a slash. When a request is processed, the HTTP Service will try to exact match the requested URI with a registered servlet. If not existent, it will remove the last ‘/’ in the URI and everything that follows, and try to match the remaining part, and so on.

An additional configuration Map can be optionally specified; if present, all the parameters contained will be copied in the ServletContext object.

Finally, an HttpContext object can be optionally specified to handle authentication, mime type and resource mapping. The HttpContext interface is quite simple:

public interface HttpContext {
    /** Returns the mime type of the specified resource */
    String getMimeType(java.lang.String name);

    /** Returns the URL to retrieve the specified resource */
    URL getResource(java.lang.String name);

    /** Manages security for the specified request */
    boolean handleSecurity(HttpServletRequest request, HttpServletResponse response);
}

The use of a custom HttpContext is typical when you want to serve static contents with the HTTP Service. Let's first see an example of resource registration without HttpContext:

public class Activator implements BundleActivator {
    private ServiceTracker httpTracker;

    public void start(BundleContext context) throws Exception {
        httpTracker = new ServiceTracker(context, HttpService.class.getName(), null) {
          public void removedService(ServiceReference reference, Object service) {
            // HTTP service is no longer available, unregister our resources...
            try {
               ((HttpService) service).unregister("/static");
            } catch (IllegalArgumentException exception) {
               // Ignore; servlet registration probably failed earlier on...
            }
          }

          public Object addingService(ServiceReference reference) {
            // HTTP service is available, register our resources...
            HttpService httpService = (HttpService) this.context.getService(reference);
            try {
              httpService.registerResources("/static", "/etc/www", null);
            } catch (Exception exception) {
              exception.printStackTrace();
            }
            return httpService;
          }
      };
      // start tracking all HTTP services...
      httpTracker.open();
    }

    public void stop(BundleContext context) throws Exception {
      // stop tracking all HTTP services...
      httpTracker.close();
    }
}

As a result of the httpService.registerResources("/static", "/etc/www", null) code, all the files available under /etc/www will be exposed under /static (e.g. http://localhost:8080/static/001.jpg will render the /etc/www/001.jpg). However, the example above can be simplistic in practice; the HttpContext object is the solution to customize the resource handling.

For instance, you can set the define more complex URI to file mappings overriding the HttpContext.getResource method, or the correct MIME type implementing the method HttpContext.getMimeType like in the example:

//....
public String getMimeType(String file) {
    if (file.endsWith(".jpg") {
        return "image/jpeg";  
    } else if (file.endsWith(".png")) {
        return "image/png";  
    } else {  
        return "text/html";  
    }
}
//....

If you implement a customised HttpContext object, don't forget to specify it as third parameter of the registerResources method invocation:

// ....
public Object addingService(ServiceReference reference) {
    // HTTP service is available, register our resources...
    HttpService httpService = (HttpService) this.context.getService(reference);
    try {
        // explicitly use our own context as 3rd parameter...
        httpService.registerResources("/static", "/etc/www", new MyHttpContext());
    } catch (Exception exception) {
        exception.printStackTrace();
    }
    return httpService;
}
// ....

Using the Servlet Bridge

The servlet bridge is used if you want to use the HTTP service inside a WAR deployed on a 3rd part applicaiton server. A little setup is needed for this to work:

1. deploy org.apache.felix.http.proxy jar file inside the web application (WEB-INF/lib);
2. in a startup listener (like ServletContextListener) set the BundleContext as a servlet context attribute (see example;
3. define org.apache.felix.http.proxy.ProxyServlet inside your web.xml and register it to serve on all requests /* (see example;
4. define org.apache.felix.http.proxy.ProxyListener as a <listener> in your web.xml to allow HTTP session related events to be forwarded (see the section of Servlet API Event forwarding below and example;
5. be sure to add javax.servlet;javax.servlet.http;version=2.6 to OSGi system packages (org.osgi.framework.system.packages);
6. deploy org.apache.felix.http.bridge (or org.apache.felix.http.bundle) inside the OSGi framework.

A detailed example can be found here.

Using the SSL filter

This filter provides you means to transparently handle SSL termination proxies, allowing your servlets and filters to work like they were accessed directly through HTTPS. This filter is useful when deploying applications in large datacenters where frontend load-balancers distribute the load among several servers in the same datacenter by stripping the SSL encryption.

The SSL filter can be configured to let it detect whether the request was originating from an SSL connection. There are several non-standard request headers in use:

In case a client connected using a certificate, this certificate can be forwarded as well by the SSL filter. Several non-standard request headers are used for this:

Note: instead of deploying the SSL filter bundle, you can also set the org.apache.felix.proxy.load.balancer.connection.enable property to true in order to achieve the same effect.

Configuration Properties

The service can both be configured using OSGi environment properties and using Configuration Admin. The service PID for this service is "org.apache.felix.http". If you use both methods, Configuration Admin takes precedence. The following properties can be used (some legacy property names still exist but are not documented here on purpose):

All-in-one-bundle configuration properties

Additionally, the all-in-one bundle uses the following environment properties (no support for Configuration Admin):

Multiple Servers

It is possible to configure several Http Services, each running on a different port. The first service can be configured as outlined above using the service PID for "org.apache.felix.http". Additional servers can be configured through OSGi factory configurations using "org.apache.felix.http" as the factory PID. The properties for the configuration are outlined as above.

The default server using the PID "org.apache.felix.http" can be disabled by specifying a negative port and then all servers can be used through factory configurations.

CometD configuration properties

The CometD bundle supports the following configuration options, using the PID org.apache.felix.http.cometd or through environment properties:

SSL filter configuration properties

The SSL-filter bundle supports the following configuration options, using the PID org.apache.felix.http.sslfilter.SslFilter (no fallback to environment properties!):

HTTP port settings

As of HTTP Jetty version 2.2.2, it is possible to assign a free port for HTTP or HTTPS automatically, based on certain rules, for example, a range between 8000 and 9000. The syntax is based on the version ranges, as described in the OSGi specification. The following forms are supported:

• * or 0: binds to the first available port;
• 8000: binds to port 8000, failing if this port is already taken;
• [8000,9000]: binds to a free port in the range 8000 (inclusive) and 9000 (inclusive);
• [8000,9000): binds to a free port in the range 8000 (inclusive) and 9000 (exclusive);
• (8000,9000]: binds to a free port in the range 8000 (exclusive) and 9000 (inclusive);
• (8000,9000): binds to a free port in the range 8000 (exclusive) and 9000 (exclusive);
• [,9000): binds to a free port in the range 1 (inclusive) and 9000 (exclusive);
• [8000,): binds to a free port in the range 8000 (inclusive) and 65535 (exclusive).

Note that picking a port is not performed atomically and multiple instances can try to bind to the same port at the same time.

Servlet API Events

The Servlet API defines a number of EventListener interfaces to catch servlet or filter related events. As of HTTP Service 2.1.0 most events generated by the servlet container are forwarded to interested service. To be registered to receive events services must be registered with the respective EventListener interface:

Of the defined EventListener interfaces in the Servlet API, the javax.servlet.ServletContextListener events are currently not support (but will be in the near future). For one thing they do not make much sense in an OSGi environment. On the other hand they are hard to capture and propagate. For example in a bridged environment the contextInitialized event may be sent before the framework and any of the contained bundles are actually ready to act. Likewise the contextDestroyed event may come to late.

Servlet Context Notes

ServletContext instances are managed internally by the Http Service implementation. For each HttpContext instance used to register one or more servlets and/or resources a corresponding ServletContext instance is created. These ServletContext instances is partly based on the single ServletContext instance received from the Servlet Container --- either embedded Jetty or some external Servlet Container when using the Http Service Bridge --- and partly based on the provided HttpContext instance:

Examples

A set of simple examples illustrating the various features are available.

• Whiteboard sample: https://github.com/apache/felix-dev/tree/master/http/samples/whiteboard
• Servlet bridge sample: https://github.com/apache/felix-dev/tree/master/http/samples/bridge/
• CometD sample: https://github.com/apache/felix-dev/tree/master/http/samples/cometd/

Maven Artifacts

This is a list of the most recent artifacts at the time of writing this document. There might already be never versions available:

<dependency>
    <groupId>org.apache.felix</groupId>
    <artifactId>org.apache.felix.http.servlet-api</artifactId>
    <version>1.1.2</version>
</dependency>
<dependency>
    <groupId>org.apache.felix</groupId>
    <artifactId>org.apache.felix.http.jetty</artifactId>
    <version>4.0.14</version>
</dependency>
<dependency>
    <groupId>org.apache.felix</groupId>
    <artifactId>org.apache.felix.http.bridge</artifactId>
    <version>4.0.8</version>
</dependency>
<dependency>
    <groupId>org.apache.felix</groupId>
    <artifactId>org.apache.felix.http.cometd</artifactId>
    <version>2.3.2</version>
</dependency>
<dependency>
    <groupId>org.apache.felix</groupId>
    <artifactId>org.apache.felix.http.proxy</artifactId>
    <version>3.0.6</version>
</dependency>
<dependency>
    <groupId>org.apache.felix</groupId>
    <artifactId>org.apache.felix.http.sslfilter</artifactId>
    <version>1.2.6</version>
</dependency>