Corso di Applicazioni Telematiche

Transcription

1 XMPP Extensible Messaging and Presence Protocol Corso di Applicazioni Telematiche A.A Prof. Simon Pietro Romano Università degli Studi di Napoli Federico II Facoltà di Ingegneria

2 XMPP: extensible Messaging and Presence Protocol Formerly known as Jabber Jeremie Miller began the project in 1998 first release in May 2000 The project's main product was jabberd XML-based Extensible to other features Open open standard open source implementations open system

3 XMPP: extensible Messaging and Presence Protocol Standardization IETF XMPP Working Group (2002) RFC 3920: Core features RFC 3921: Instant Messaging and Presence

4 RFC 3920: Overview and Architecture is a protocol for streaming Extensible Markup Language (XML) elements in order to exchange structured information in close to real time between any two network endpoints Architecture s2s XMPP XMPP XMPP XMPP XMPP XMPP servers Client Server Server Manage TCP connections route messages No-XMPP Foreign server-to-server (5269) XMPP messagi Gateway Client ng XMPP XMPP clients network connect to server (5222) multiple resources simultaneously Gateway translates XMPP into the protocol used by a foreign (non-xmpp) messaging system XMPP No-XMPP XMPP Client Foreign Messaging Client

5 RFC 3920: Addressing Scheme All XMPP entities are uniquely addressable JID (Jabber Identifier) [ node "@" ] domain [ "/" resource ] domain identifier: FQDN / address-literal FQDN (Fully Qualified Domain Name ): (sub-domain_1)". (sub- domain) address-literal: IPv4address / IPv6address usually represents servers or gateways (REQUIRED) node identifier a simple string usually represents a client (OPTIONAL) resource identifier usually represents a specific session, connection or object belonging to the entity associated with a node identifier (OPTIONAL).

6 JID: examples domain meetecho.com 6

7 XML example XML-based communication

8 RFC 3920: XML Stream XML Stream container for the exchange of XML Stanzas between any two entities over a network start <stream> tag with appropriate attributes and namespace end </stream> tag the stream enables unidirectional communication qualified by the default namespace for the stream jabber:client (client and server ) jabber:server (server-to-server)

9 Stream example 1. Client initiates stream to server <?xml version='1.0'?> <stream:stream to='example.com' xmlns='jabber:client' xmlns:stream=' version='1.0'> 2. Server responds by sending a stream tag to client <?xml version='1.0'?> <stream:stream from='example.com' id='someid' xmlns='jabber:client' xmlns:stream=' version='1.0'> encryption, authentication, and resource binding 9

10 Encryption: use of TLS Method for securing the stream Transport Layer Security (TLS) protocol "STARTTLS" extension namespace name 'urn:ietf:params:xml:ns:xmpp-tls 3. Server sends the STARTTLS extension to client <stream:features> <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'> <required/> </starttls> <mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'> <mechanism>digest-md5</mechanism> <mechanism>plain</mechanism> </mechanisms> </stream:features> 10

11 Use of TLS (2) 4. Client sends the STARTTLS command to server <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/> 5. Server informs client that it is allowed to proceed <proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/> 6. Client and server attempt to complete TLS negotiation over the existing TCP connection 7. If TLS negotiation is successful, client initiates a new stream to server 8. Server responds by sending a stream header to client along with any available stream features 9. Client continues with SASL negotiation 11

12 RFC 3920: XML Stanza XML Stanza discrete semantic unit of structured information that is sent over an XML stream exists at the direct child level of the root exists at the direct child level of the root <stream> element

13 XMPP stanzas defined stanzas are: <message> entity pushes information to another entity <presence> availaibility information <iq> info/query request-response mechanism qualified by the default namespace for the stream Common Attributes to, from, type, id, xml:lang <message type='chat' <body>art thou not Romeo, and a Montague?</body> </message> 13

14 RFC 3921: Instant Messaging and Presence Describes extensions to and applications of the core features XMPP that provide the basic instant messaging (IM) and presence functionality Requirements Requirements Exchange messages with other users Exchange presence information with other users Manage subscriptions to and from other users Manage items in a contact list (in XMPP this is called a "roster") Block communications to or from specific other users

15 RFC 3921: Message Syntax Possible values of types for Message packets chat: sent in the context of a one-to-one chat groupchat: sent in the context of a multi-user chat Child Elements <subject/> contains the topic of the message <body/> the textual content of the message <thread/> identifier that is used for tracking a conversation thread <message to='romeo@ex.net' from='juliet@exm.com/balcony' type='chat' xml:lang='en'> <subject>the balcony scene!</subject> <subject xml:lang= it'>la scena del balcone!</subject> <body>wherefore art thou, Romeo?</body> <body xml:lang= it'>perché sei tu, Romeo?</body> </message>

16 RFC 3921: Presence Syntax Possible values of types for Presence packets subscribe: the sender wishes to subscribe to the recipient's presence unavailable: signals that the entity is no longer available probe: request for an entity's current presence Child Elements <show/> specifies the particular availability status away, chat, dnd = "Do Not Disturb and xa = "extended Away" <status/> a description of availability status <priority/> the priority level of the resource [-128, +127] <presence xml:lang='en'> <show>dnd</show> <status>wooing Rupert</status> <priority>1</priority> </presence>

17 RFC 3921: IQ Syntax Extended namespace defines all data contained within the child element Possible values of types for IQ packets get set result Use case: retrieving One's Roster on Login 'jabber:iq:roster' namespace <iq type='get' id='roster_1'> <query xmlns='jabber:iq:roster'/> </iq> <iq type='result' id='roster_1'> <query xmlns='jabber:iq:roster'> <item name='romeo subscription='both'> <group>friends</group> </item> </query> </iq>

18 XEP: XMPP Extension Protocol XEP-0166: Jingle Is a pure XMPP signalling protocol Designed to interwork with SIP Initiating and managing media sessions between two XMPP entities negotiation occurs over the XMPP "channel" media is exchanged outside the XMPP using RTP, UDP. How it works: File transfer Romeo Juliet session-initiate ack session-accept ack MEDIA SESSION session-terminate ack

19 XEP: XMPP Extension Protocol XEP-0166: Jingle Is a pure XMPP signalling protocol id='jingle1' to= juliet@shakespeare.lit/castle' Designed to interwork with SIP type='set'> Initiating and managing media sessions between two XMPP entities action='session-initiate' initiator= romeo@shakespeare.lit/castle' negotiation sid='851ba2'> occurs over the XMPP "channel" <content creator='initiator' name='a-file-offer'> <description media is exchanged xmlns='urn:xmpp:tmp:jingle:apps:file-transfer'> outside the XMPP using RTP, UDP. <offer> How it works: File transfer <iq from= romeo@shakespeare.lit/castle' <jingle xmlns='urn:xmpp:tmp:jingle' <file xmlns=' name='test.txt' size='1022' hash='552da c69ae5d2141d3766b1' date=' t02:56:15z'> Romeo <desc>this is a test. If this were a real file...</desc> transfer' </content> </jingle> </iq> Juliet session-initiate ack </file> </offer> </description> <transport xmlns='urn:xmpp:tmp:jingle:transports:bytestreams'/> session-accept ack MEDIA SESSION session-terminate ack

20 XEP: XMPP Extension Protocol XEP-0166: Jingle Is a pure XMPP signalling protocol Designed to interwork with SIP Initiating and managing media sessions between two XMPP entities negotiation occurs over the XMPP "channel" media is exchanged outside the XMPP using RTP, UDP. How it works: File transfer Romeo Juliet session-initiate ack session-accept ack <iq from= juliet@shakespeare.lit/castle' MEDIA SESSION id='jingle1' to= romeo@shakespeare.lit/castle' session-terminate type='result'/> ack

21 XEP-0167: Jingle Audio via RTP This document specifies an application format for negotiating Jingle audio sessions, where the media is exchanged over the Realtime Transport Protocol Mapping to Session Description Protocol m=<media> <port> <transport> <fmt list> In the context of Jingle audio sessions <media> = audio <port> is the preferred port <transport> is whatever profile is negotiated <fmt list> is the payload-type ID static payload-type: dynamic payload-type <payload-type id='96' name='speex' clockrate='16000' ptime='40'> <parameter name='vbr' value='on'/> <parameter name='cng' value='on'/> </payload-type> <payload-type id="13" name="cn"/> m=audio 9999 RTP/AVP 13 m=audio 9999 RTP/AVP 96 a=rtpmap:96 speex/16000

22 Strengths Decentralization anyone can run his own XMPP server there is no central master server Open standards No royalties are required to implement support of these specifications History Multiple implementations of the XMPP standards exist for clients, servers, components, and code libraries Security XMPP servers may be isolated from the public Jabber network (e.g., on a company intranet) Flexibility Custom functionality can be built on top of XMPP

23 Weaknesses Presence data overhead With typically over 70% of XMPP inter-server traffic being presence data, and close to 60% of it being redundantly transmitted No binary data The way XMPP is encoded as a single long XML document makes it impossible to deliver unmodified binary data File transfers are therefore arranged to happen using external protocols like HTTP If unavoidable, XMPP also provides in-band file transfers by encoding all data using base64 Other binary data like encrypted conversations or graphic icons are embedded using the same method.

24 Demo scenario XMPP Client XMPP Client XMPP clienttoserver.xml XMPP Server XMPP Server 24

25 Open source XMPP servers chime (Java) DJabberd (Perl) ejabberd (Erlang) Home page and Community Site jabberd14 (C) jabberd2 (C) Openfire (Wildfire) (Java) OpenIM (Java) Pretzel (Python) psyced (LPC) Tigase (Java) WPJabber (C) xmppd.py (Python)

26 and free clients Bombus J2ME (MIDP2.0)/WinCE Bombusmod J2ME (MIDP2.0) Coccinella Cross-platform Tcl/Tk Exodus Windows Gabber Linux/Unix GTK+ Gajim Cross-platform GTK+ GOIM Cross-platform Eclipse Rich Client Platform Spark Cross-platform Java Gossip Linux/Unix GTK+ Jabbim Cross-platform PyQt Jabbin Cross-platform Qt MCabber Cross-platform (ncurses) Mobber J2ME (MIDP1.0) MOO-XMPP MOO Psi Cross-platform Qt Tapioca Tkabber Cross-platform Tcl/Tk Wija Java

27 References XMPP Working Group Charter RFC 3920 XMPP: Core RFC 3921 XMPP: Instant Messaging and Presence XEP-0166: Jingle

28 Domande? 28