Smack/documentation/providers.md

Provider Architecture: Stanza Extensions and Custom IQ's

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Introduction

The Smack provider architecture is a system for plugging in custom XML parsing of packet extensions and IQ packets. The standard Smack Extensions are built using the provider architecture. There are two types of providers:

• IQProvider -- parses IQ requests into Java objects.
• Extension Provider -- parses XML sub-documents attached to packets into ExtensionElement instances. By default, Smack only knows how to process a few standard packets and sub-packets that are in a few namespaces such as:
  • jabber:iq:auth
  • jabber:iq:roster
  • jabber:iq:register

There are many more IQ types and extensions that are part of XMPP standards, and of course an endless number that can be added as custom extensions. To support this, an extensible parsing mechanism is provided via Smack and user build providers.

Whenever a packet extension is found in a packet, parsing will be passed to the correct provider. Each provider must extend the ExtensionElementProvider abstract class. Each extension provider is responsible for parsing the raw XML stream, via the Smack's XmlPullParser interface, to construct an object.

You can also create an introspection provider (provider.IntrospectionProvider.PacketExtensionIntrospectionProvider). Here, bean introspection is used to try to automatically set the properties of the class using the values in the packet extension sub-element.

When no extension provider is registered for an element name and namespace combination, Smack will store all top-level elements of the sub-packet in the StandardExtensionElement object and then attach it to the packet.

Management of these providers is accomplished via the ProviderManager class. There are multiple ways to add providers to the manager.

• Call addXXProvider methods - You can call the appropriate add methods directly.

ProviderManager.addIQProvider("element", "namespace", new MyIQProvider());
ProviderManager.addExtensionProvider("element", "namespace", new MyExtProvider());

• Add a loader - You can add a ProviderLoader which will inject a means of loading multiple providers (both types) into the manager. This is the mechanism used by Smack to load from the Smack specific file format (via ProviderFileLoader). Implementers can provide the means to load providers from any source they wish, or simply reuse the ProviderFileLoader to load from their own provider files.

  ProviderManager.addLoader(new ProviderFileLoader(FileUtils.getStreamForUrl("classpath:com/myco/provider/myco_custom.providers", null)));

• VM Argument - You can add a provider file via the VM argument smack.provider.file. This will load the file at the specified URL during startup when Smack initializes. This also assumes the default configuration, since it requires that the VmArgInitializer was part of the startup configuration.

-Dsmack.provider.file=classpath:com/myco/provider/myco_custom.providers

or

-Dsmack.provider.file=file:///c:/myco/provider/myco_custom.providers

IQ Providers

The IQ provider class must extend the IQProvider abstract class. Each IQProvider is responsible for parsing the raw XML stream to create an IQ instance.

You can also create an introspection provider (provider.IntrospectionProvider.IQIntrospectionProvider). Which uses bean introspection to try to automatically set properties of the IQ instance using the values found in the IQ packet XML. For example, an XMPP time packet resembles the following:

Introspection

Time Stanza

<iq type='result' to='joe@example.com' from='mary@example.com' id='time_1'>
	<query xmlns='jabber:iq:time'>
		<utc>20020910T17:58:35</utc>
		<tz>MDT</tz>
		<display>Tue Sep 10 12:58:35 2002</display>
	</query>
</iq>

Time IQ Class

class Time extends IQ {
	private Date utc;
	private TimeZone timeZone;
	private String display;

	@Override
	public String getChildElementXML() {
		return null;
	}

	public void setUtc(String utcString) {
		try {
			utc = StringUtils.parseDate(utcString);
		} catch (ParseException e) {
		}
	}

	public void setTimeZone(String zone) {
		timeZone = TimeZone.getTimeZone(zone);
	}

	public void setDisplay(String timeDisplay) {
		display = timeDisplay;
	}
}

Time Provider

public class TimeProvider extends IQIntrospectionProvider<Time> {

    public TimeProvider() {
        super(Time.class);
    }

}

The introspection service will automatically try to convert the String value from the XML into a boolean, int, long, float, double, or Class depending on the type the IQ instance expects.

Custom IQProvider example

Let's assume you want to write a provider for a new, unsupported IQ in Smack.

Custom IQ

<iq type='set' from='juliet@capulet.example/balcony' to='romeo@montage.example'>
  <myiq xmlns='example:iq:foo' token='secret'>
    <user age='42'>John Doe</user>
    <location>New York</location>
  </myiq>
</iq>

Custom IQ Provider

public class MyIQProvider extends IQProvider<MyIQ> {

  @Override
  public MyIQ parse(XmlPullParser parser, int initialDepth) throws XmlPullParserException, IOException {
    // Define the data we are trying to collect with sane defaults
    int age = -1;
    String user = null;
    String location = null;

    // Start parsing loop
    outerloop: while(true) {
      XmlPullParser.Event eventType = parser.next();
      switch(eventType) {
      case START_ELEMENT:
        String elementName = parser.getName();
        switch (elementName) {
        case "user":
          age = ParserUtils.getIntegerAttribute(parser, "age");
          user = parser.nextText();
          break;
        case "location"
          location = parser.nextText();
          break;
        }
        break;
      case END_ELEMENT:
        // Abort condition: if the are on a end tag (closing element) of the same depth
        if (parser.getDepth() == initialDepth) {
          break outerloop;
        }
        break;
      default:
        // Catch all for incomplete switch (MissingCasesInEnumSwitch) statement.
        break;
      }
    }

    // Construct the IQ instance at the end of parsing, when all data has been collected
    return new MyIQ(user, age, location);
  }
}

DiscoItemsProvider

Disco Items Stanza

<iq type='result' from='shakespeare.lit' to='romeo@montague.net/orchard' id='items1'>
   <query xmlns='http://jabber.org/protocol/disco#items'>
	   <item jid='people.shakespeare.lit' name='Directory of Characters'/>
	   <item jid='plays.shakespeare.lit' name='Play-Specific Chatrooms'/>
	   <item jid='mim.shakespeare.lit' name='Gateway to Marlowe IM'/>
	   <item jid='words.shakespeare.lit' name='Shakespearean Lexicon'/>
	   <item jid='globe.shakespeare.lit' name='Calendar of Performances'/>
	   <item jid='headlines.shakespeare.lit' name='Latest Shakespearean News'/>
	   <item jid='catalog.shakespeare.lit' name='Buy Shakespeare Stuff!'/>
	   <item jid='en2fr.shakespeare.lit' name='French Translation Service'/>
   </query>
</iq>

Disco Items IQProvider

public class DiscoverItemsProvider implements IQProvider<DiscoverItems> {

	public DiscoverItems parseIQ(XmlPullParser parser, int initialDepth) throw XmlPullParserException, IOException {
		DiscoverItems discoverItems = new DiscoverItems();
		DiscoverItems.Item item;
		String jid = "";
		String name = "";
		String action = "";
		String node = "";
		discoverItems.setNode(parser.getAttributeValue("", "node"));
		outerloop: while (true) {
			XmlPullParser.Event eventType = parser.next();
			switch (eventType) {
			case START_ELEMENT:
				String elementName = parser.getName();
				switch (elementName) {
				case "item":
					// Initialize the variables from the parsed XML
					jid = parser.getAttributeValue("", "jid");
					name = parser.getAttributeValue("", "name");
					node = parser.getAttributeValue("", "node");
					action = parser.getAttributeValue("", "action");
					break;
				}
				break;
			case END_ELEMENT:
				String elementName = parser.getName();
				switch (elementName) {
				case "item":
					// Create a new Item and add it to DiscoverItems.
					item = new DiscoverItems.Item(jid);
					item.setName(name);
					item.setNode(node);
					item.setAction(action);
					discoverItems.addItem(item);
					break;
				case "query":
				    if (parser.getDepth() == initialDepth) {
						break outerloop;
					}
					break;
				}
			}
		}
		return discoverItems;
	}
}

Extension Providers

Stanza extension providers are responsible for parsing packet extensions, which are child elements in a custom namespace of IQ, message and presence packets.

Pubsub Subscription Stanza

<iq type='result' from='pubsub.shakespeare.lit' to='francisco@denmark.lit/barracks' id='sub1'>
   <pubsub xmlns='http://jabber.org/protocol/pubsub'>
	   <subscription node='princely_musings' jid='francisco@denmark.lit' subscription='unconfigured'>
		   <subscribe-options>
			   <required/>
		   </subscribe-options>
	   </subscription>
   </pubsub>
</iq>

Subscription PacketExtensionProvider Implementation

public class SubscriptionProvider extends ExtensionElementProvider<ExtensionElement> {
	public ExtensionElement parse(XmlPullParser parser) throws Exception {
		String jid = parser.getAttributeValue(null, "jid");
		String nodeId = parser.getAttributeValue(null, "node");
		String subId = parser.getAttributeValue(null, "subid");
		String state = parser.getAttributeValue(null, "subscription");
		boolean isRequired = false;

		XmlPullParser.Event tag = parser.next();

		if ((tag == XmlPullParser.START_ELEMENT) && parser.getName().equals("subscribe-options")) {
			tag = parser.next();

			if ((tag == XmlPullParser.START_ELEMENT) && parser.getName().equals("required"))
				isRequired = true;

			while (parser.next() != XmlPullParser.END_ELEMENT && parser.getName() != "subscribe-options");
		}
		while (parser.getEventType() != XmlPullParser.END_ELEMENT) parser.next();
		return new Subscription(jid, nodeId, subId, state == null ? null : Subscription.State.valueOf(state), isRequired);
	}
}

Provider file format

This is the format for a provider file which can be parsed by the ProviderFileLoader.

<?xml version="1.0"?>
<smackProviders>
<iqProvider>
	<elementName>query</elementName>
	<namespace>jabber:iq:time</namespace>
	<className>org.jivesoftware.smack.packet.Time</className>
</iqProvider>

<iqProvider>
	<elementName>query</elementName>
	<namespace>http://jabber.org/protocol/disco#items</namespace>
	<className>org.jivesoftware.smackx.provider.DiscoverItemsProvider</className>
</iqProvider>

<extensionProvider>
	<elementName>subscription</elementName>
	<namespace>http://jabber.org/protocol/pubsub</namespace>
	<className>org.jivesoftware.smackx.pubsub.provider.SubscriptionProvider</className>
</extensionProvider>
</smackProviders>

Each provider is associated with an element name and a namespace. If multiple provider entries attempt to register to handle the same namespace, the last entry added to the ProviderManager will overwrite any other that was loaded before it.

Copyright (C) Jive Software 2002-2008