Overview

Smack is a library for client-to-server XMPP connections to perform real-time communications and data exchange. This includes, but is not limited to, instant messaging and group chat. More generically speaking, it allows you to easily exchange data in various ways: For example fire-and-forget, publish-subscribe, between human and non-human endpoints. The use cases include M2M, IoT, and many more.

Smack is a pure Java library, open-source and highly modular. It runs on Android and Java SE. The API strives to be easy to use but yet powerful.

Key Advantages

{@code
AbstractXMPPConnection connection = new XMPPTCPConnection("mtucker", "password", "jabber.org");
connection.connect().login();

Message message = connection.getStanzaFactory()
   .buildMessageStanza()
   .to("jsmith@igniterealtime.org")
   .setBody("Howdy! How are you?")
   .build();

connection.sendStanza(message);

connection.disconnect();
}

Smack doesn't force you to code at the protcol level of XMPP. The library provides intelligent higher level constructs, often called {@link org.jivesoftware.smack.Manager}, which let you program more efficiently. Other examples of those constructs are the Chat and Roster classes.

Smack comes with APIs for easy machine-to-machine communication. You can set any number of properties on each message, including properties that are Java objects.

License

Smack is open-source and most parts are under the Apache License 2.0, which means you can incorporate Smack into your commercial or non-commercial applications. Some parts of Smack may be under a different open-source license. Please refer to the individual subprojects for their license statement.

Note that the Apache License 2.0 requires that the contents of a NOICE text file are shown "…within a display generated by the Derivative Works, if and wherever such third-party notices normally appear.". Smack comes with such a NOTICE file. The content of Smack's NOTICE file can conveniently be retrieved using {@link org.jivesoftware.smack.Smack#getNoticeStream}.

About XMPP

XMPP (eXtensible Messaging and Presence Protocol) is an open protocol standardized by the Internet Engineering Task Force (IETF) and supported and extended by the XMPP Standards Foundation (XSF).

Smack Modules

Smack is meant to be easily embedded into any existing Java application. The library ships as several modules to provide more flexibility over which features applications require.

• smack-core -- provides core XMPP functionality. All XMPP features that are part of the XMPP RFCs are included.
• smack-im -- provides functionality defined in RFC 6121 (XMPP-IM), like the Roster.
• {@link org.jivesoftware.smack.tcp smack-tcp} -- support for XMPP over TCP. Includes XMPPTCPConnection class, which you usually want to use
• smack-extensions -- support for many of the extensions (XEPs) defined by the XMPP Standards Foundation, including multi-user chat, file transfer, user search, etc. The extensions are documented in the [extensions manual](extensions/index.md).
• smack-experimental -- support for experimental extensions (XEPs) defined by the XMPP Standards Foundation. The API and functionality of those extensions should be considered as unstable.
• smack-legacy -- support for legacy extensions (XEPs) defined by the XMPP Standards Foundation.
• smack-bosh -- support for BOSH (XEP-0124). This code should be considered as beta.
• smack-resolver-minidns -- support for resolving DNS SRV records with the help of MiniDNS. Ideal for platforms that do not support the javax.naming API. Also supports [DNSSEC](dnssec.md) TODO: Fix link.
• smack-resolver-dnsjava -- support for resolving DNS SRV records with the help of dnsjava.
• smack-resolver-javax -- support for resolving DNS SRV records with the javax namespace API.
• smack-debug -- an enhanced GUI debugger for protocol traffic. It will automatically be used when found in the classpath and when [debugging](debugging.md) is enabled.

Main API Entry Points

• {@link org.jivesoftware.smack.XMPPConnection}
• {@link org.jivesoftware.smack.tcp.XMPPTCPConnection}
• {@link org.jivesoftware.smack.roster.Roster}

Smack Extensions

Since the X in XMPP stands for eXstensible, Smack comes with many built-in extensions for XMPP. Click

{@link org.jivesoftware.smackx}

for an overview of all supporteted XMPP extensions of Smack.

• {@link org.jivesoftware.smackx.muc.MultiUserChat Multi-User Chat (XEP-0045)}
• {@link org.jivesoftware.smackx.carbons.CarbonManager Message Carbons (XEP-0289)}
• {@link org.jivesoftware.smackx.omemo OMEMO (XEP-0384)}

Configuration

Smack has an initialization process that involves 2 phases.

• Initializing system properties - Initializing all the system properties accessible through the class **SmackConfiguration**. These properties are retrieved by the _getXXX_ methods on that class.
• Initializing startup classes - Initializing any classes meant to be active at startup by instantiating the class, and then calling the _initialize_ method on that class if it extends **SmackInitializer**. If it does not extend this interface, then initialization will have to take place in a static block of code which is automatically executed when the class is loaded.

Initialization is accomplished via a configuration file. By default, Smack will load the one embedded in the Smack jar at _org.jivesoftware.smack/smack- config.xml_. This particular configuration contains a list of initializer classes to load. All manager type classes that need to be initialized are contained in this list of initializers.