goffi goffi

Let's talk XMPP - episode 4 - group conversations

This article was initially published in French, and it got some interest, so we started to translate the whole series in English. If you can read French, you can follow the whole series there: http://www.goffi.org/tag/parlons_xmpp

The translation to English was done thanks to: Poulet , Éfrit , Paco , mbarbarosa , Weyfonk and Chteufleur . The whole series is under CC By-SA , and any help would be appreciated to help with the translation of next articles.
(Follow the corresponding link to read the previous episodes).

In the software development field, and much in the libre software, group’s discussions are really common, mostly with IRC (Internet Relay chat).
This venerable protocol do what we ask it and XMPP is strongly inspired by it. Let’s see that closely.

Group’s discussions used nowadays are called MUC (Multi-User Chat) and are defined by XEP-0045. This one standardizes and extends the first solution called Groupchat. As all that comes from IRC, I’ll explain as they come the major differences between them.

It is possible to acces a chat room located on any server from any server (again, while it is not explicitly prohibited). Chat rooms do, as the users, have a jid, which has the pattern chat_room_name@service. For example, that of Salut à Toi is sat@chat.jabberfr.org:  “sat” is the chat room’s name, “chat.jabberfr.org” the service.

The resource is used for occupants of the chat room: sat@chat.jabberfr.org/goffi corresponds to the occupant “goffi” in the chat room sat@chat.jabberfr.org. Ah little detail that I forgot in previous articles: everything is unicode in XMPP, including jid. So you can use arabic or russian nickname. But beware: some unicode characters are strongly similar, therefore it is possible to get 2 words graphically similar mixed up, we name it “homoglyphs”. For example “gοffⅰ” looks like “goffi” but it uses different characters. This issue is mentioned in a unicode technical report: http://www.unicode.org/reports/tr36/. Also, do not rely exclusively on a nickname to identify someone (espcially that it is possible that it can be reused by someone else between two sessions).

The nickname is linked to the chat room and not to the service. You can have a nick “toto” in a chat room and “titi” in another one, and someone else can have “titi” on a third chat room. This is a big difference with IRC where we have only one nickname on a server that will be used in every chat room (channel on IRC).

To go in or go out a chat room, or to change nickname, we send an available (or not) presence directly to chat_room@example.net/desired_nick, but this is normaly managed by your client.

It is also possible to write directly to all chat room’s occupants (under the hood this is a “groupchat” message that is sent to the chat room’s bare jid), or to have a private chat with a member (we write to the full jid of the recipient).

A chat room can be public or hidden (it will not appear in the chat room list), not anonymous or semi-anonymous (in the first case everyone can see the occupant’s real jid, in the second case only moderators and administrators can), persistent or temporary, open or accessible only by white list or can be protected by password, moderated or not.

All those parameters are normally defined at the creation of the chat room, or they can be modified after with the suitable option of your client (on Gajim: right click on chat room tab => Manage Room => Configure Room). According to the service you use, you can configure more or less things, for example limit the occupant’s maximal number.

A feature often implemented is the history or “back log”: when you get in a chat room, the service sends you the last X messages, allowing you to understand the context of the current conversation.

Also, if a public archive of the chat room is kept (we say “logged” chat room), the service must warn you (it’s mandatory in the XEP), this is another good point compared to IRC. For sure, one has to remember that anyone in the room can keep a log and could publish it without your consent.

So far, so good, but a great strength of IRC is its simplicity: no need to create an account, you just have to pick a nick (unique), with a server, and that’s it! So, you won’t be disapointed, XMPP has exactly the same thing with connections called “anonymous”. No anonymity in terms of Tor here, but rather the possibility to get a temporary account, with a jid more or less random, for the connection time. This comes built-in but it must often be explicitly enabled in the server configuration, and most of the time, anonymous connections are limited to the local network, no communication with other servers (to avoid spam).

If you want to chat as with IRC in a simple and intuitive way, and if you like the console, I would strongly recommend Poezio which is an excellent XMPP client that is easy to use: initially, without changing the configuration, you will be anonymously connected to the MUC service of Poezio. It is inspired by Irssi/Weechat and use the same commands (and more generally those of IRC). Below the welcome message, without changing the configuration, we see the anonymous jid assigned for the session time.

Poezio screenshot

Well this episode is long enough, but I am not finished with MUC, therefore we will talk about it next time, probably with transports.

Let's talk XMPP - episode 3 - core and extensions (part 2)

This article was initially published in French, and it got some interest, so we started to translate the whole series in English. If you can read French, you can follow the whole series there: http://www.goffi.org/tag/parlons_xmpp

The translation to English was done thanks to: Poulet, Éfrit, Paco, mbarbarosa, Weyfonk and Chteufleur. The whole series is under CC By-SA, and any help would be appreciated to help with the translation of next articles.
(Follow the corresponding link to read the previous episodes).
 
Some functionalities can be added to this central part, hence the X of XMPP (which stands for “eXtensible”).
 
Extensions are written using “XEP” (XMPP Extension Protocol) , following an idea taken from Python (if I am not mistaken). This is why the features supported by a server or a client are identified as XEP-0XXX. Obviously, no need to know this to use a XMPP client, but it can be useful to read an extension (you can find them at  https://xmpp.org/xmpp-protocols/xmpp-extensions/) to understand correctly the utility of a functionality. Two parts are particularly useful without the need to enter in the implementation details: the “abstract” part (summary) in the top that indicates what the XEP is doing, and the “introduction” section (the very first section) that provides further details about the cause of the extension and its use cases.
 
XEP-0045 abstract
 
An XEP can describe a feature, a process (for instance the XEP-0001 explains the life cycle of the XEPs themselves), a historical legacy (related to something created before the XMPP Standard Foundation), information (like good practices), even a joke (yes, there are also lousy jokes in the XEPs!). It can have several statuses, detailed in the XEP-0001. It is interesting to note that a lot of XEPs are “experimental” and so technically not (yet) standards, but often implemented anyway. Such XEPs can be widely modified before they get the “Draft” status and eventually become a standard.
 
Why am I talking about all this? For you to get one thing loud and clear: XMPP is not only about instant messaging!
 
Some interesting examples of extensions:
 
  • Extended Stanza Addressing (XEP-0033): to send messages to several recipients at once, or to do carbon copies, as well as blind carbon copies (as the… yes, yes you see what I mean).
  • Multi-User Chat (XEP-0045): IRC-like group chat.
  • Ad-Hoc Commands (XEP-0050): a generic system to handle any kind of commands. Related to users' permissions, it is a great tool!
  • vcard-temp (Business cards, temporary version, XEP-0054): The legacy way to manage electronic business cards, which are a kind of public profile. A new extension will eventually replace it (XEP-0292).
  • Jabber Search (XEP-0055): used to search for jid, mostly used by directories.
  • Publish/Subscribe (XEP-0060): a big piece, used to publish all kinds of information, and its recovery based on permissions, with a notification system in real time.
  • XHTML-IM (XEP-0071): to publish with an XHTML subset, which enables formatting (to write bold text or include a picture for example).
  • Gateway Interaction (XEP-0100): to manage gateways, i.e. links to external networks.
  • Personal Eventing Protocol (XEP-0163): a kind of simplified Publish/Subscribe system.
  • Jingle (XEP-0166): Peer-to-peer session establishment with a wide range of possible applications, the most well-known being video conference.
  • Serverless Messaging (XEP-0174): unsurprisingly used to communicate without servers.
  • Message Archive Management (XEP-0313): to recover messages or other objects (works with Publish/Subscribe as well) following criteria such as a date. In particular, used to get a conversation history on a server, which is useful to access it from all your clients.
 
Keep in mind that we’ve barely scratched the surface here.
 
Further details will be provided about some of these extensions in future articles.
Please note that extensions can be referred by using short names, for instance “MAM” for “Message Archive Management”. Such names are usually mentioned at the end of the related XEPs, in the “Document Information” appendices.
 
This may lead to situations where clients and servers don’t support the same extensions subsets… How to make both parties agree on which one to use? This problem is solved through another extension (though so essential and widely implemented that it could nearly be considered as a main standard): “Service Discovery”, aka XEP-030, short name: “disco”.
 
The idea is simple: each client, server or component discloses who it is, what it can do, or associated items. A component is a service that plugs itself into a server, see below.
 

who it is

An XMPP address (or jid) can be used by all kinds of elements, be it a server, a client, a gateway, or a bot for instance. The latter is a robot, i.e. a program that automates tasks, and is often used to behave like a client.
 
When a client or another element sees a jid, it may need to know what kind of element is associated to that jid, for instance to render it in a special way in the user interface. This is how clients and gateways are shown in distinct ways in your contacts list.
 
Disco’s identity provides this through a category (“client” or “server” for instance), a type (e.g. a client can be “bot”, “web”, “game”…), and a free name (eg “ejabberd”). A list of categories and their associated types can be found on  https://xmpp.org/registrar/disco-categories.html.
 

what it can do

 
XMPP’s extensibility makes it very feature-rich, therefore knowing what the software we are talking to is able to do is mandatory. Disco provides a list of such supported features, which is why you may see disabled buttons or icons (e.g. for video conference) while talking to someone. This means the client you are talking to indicates that it does not support this feature, or more accurately: it does not reveal that it supports it.
 
These features are linked to namespaces that are mentioned in the related XEPs. A list of XEPs based on namespaces is available here: https://xmpp.org/resources/schemas.
 

associated items

 
Beside its identity and available features, an XMPP entity can have associated elements. They can be servers indicating where to find chat rooms, or gateways to other networks.

 

Let's try

Let’s make this clear with an example. Salut à Toi’s command line interface “jp” can retrieve an entity’s disco using the command “jp info disco”, see below with jabber.fr:
 
 
% jp info disco jabber.fr
Features:
 
http://jabber.org/protocol/commands
http://jabber.org/protocol/disco#info
http://jabber.org/protocol/disco#items
http://jabber.org/protocol/stats
iq
jabber:iq:register
jabber:iq:time
jabber:iq:version
msgoffline
presence
presence-invisible
urn:xmpp:time
vcard-temp
--
Identities:
 
ejabberd (server/im)
--
Extensions:
 
http://jabber.org/network/serverinfo
 
--
Items:
 
[chat.jabberfr.org]
[irc.jabberfr.org]
[j2j]
[presence.jabberfr.org]
[proxy.jabberfr.org]
[users.jabberfr.org]
 
 
As we can see, jabber.fr supports legacy vCards management (vCard-temp, XEP-0054) as well as ad-hoc commands (http://jabber.org/protocol/commands, XEP-0050), and the server (server/im) used for instant messaging is called “ejabberd”. We can also notice that various services are available, one of them being char.jabberfr.org. Let’s take a closer look:
 
% jp info disco chat.jabberfr.org
Features:
 
http://jabber.org/protocol/disco
http://jabber.org/protocol/muc
http://jabber.org/protocol/muc#unique
jabber:iq:browse
jabber:iq:last
jabber:iq:register
jabber:iq:time
jabber:iq:version
urn:xmpp:ping
vcard-temp
--
Identities:
 
Public Chatrooms (conference/text)
--
Items:
 
[...]
JabberFR (13) [jabberfr@chat.jabberfr.org]
[...]
 
 
We see that we are dealing with a chat rooms service (conference/text), which use the protocol “Multi-User Chat” (http://jabber.org/protocol/muc). It is at the moment the only one which is available for groups’ discussions (we will talk about it later). “Items” elements contain rooms’ list, with the name, the occupiers’ number with the corresponding JID. I shorten the list which was very long.
 
In jabber.fr’s information, you may have noticed the “extensions” section, it is the XEP-0128 which allow to extend disco for all kind of information. In the case of ejabberd here, it is to give contact addresses of server, but they aren’t indicated for jabber.fr
 
Below the disco’s window of Gajim:
 
Gajim disco
The first time I used XMPP, with Psi in the early 2000s, I was a bit intimidated by the “service discovery” menu, which shows near directly all information we just saw. This kind of menu is often, at my opinion, showed too abruptly in XMPP clients: using disco directly (that is all except what is automated by the client) is already advanced use.
 
 
Furthermore, I will quickly mention the “software version” extension (XEP-0092) which allows, as indicated by its name, to know to which software we are talking to, and the operating system used. jp allows to show these information with “jp info version”, let’s try on jabber.fr:
 
% jp info version jabber.fr
Client name: ejabberd
Client version: 2.1.13
Operating System: unix/linux 3.2.0
 
We now know the ejabberd version that is used. Useful when we know if a feature is supported or if a bug is fixed. And this work with every entity which implement the XEP, not only servers.
 
% jp info version chat.jabberfr.org
Client name: MU-Conference
Client version: 0.9-svn (Jan 27 2014)
Operating System: Linux 3.2.0-4-amd64
 
That’s it. Knowing about the extensions allows to truly know what we can do with a client or a server. Next time I think I will explain groups’ discussions and see what changed in relation to IRC.

Let's talk XMPP - episode 2 - core and extensions

This article was initially published in French, and it got some interest, so we started to translate the whole series in English. If you can read French, you can follow the whole series there: http://www.goffi.org/tag/parlons_xmpp

The translation to English was done thanks to: Poulet, Éfrit, Paco and mbarbarosa and Weyfonk. The whole series is under CC By-SA, and any help would be appreciated to help with the translation of next articles.

Now that we know what we’re talking about, let’s see what the core of the protocol looks like.
 
Originally, XMPP is defined by 3 (previously 2) RFCs: RFC 6120, RFC 6121, and RFC 6122 (there are others, but these 3 are the main ones). They explain the core of the system, such as sending messages, presence information, statuses and so on.
 
Without getting too much into details related to developers, we can quickly explain that XMPP is based on 3 element types, or “stanzas”:
  • <presence/> to primarily indicate… our presence information (sometimes, we also add other things like our avatars, our capabilities, but let’s stay focused). The presence is broadcast by the server to all the people that you have given permission to (see below).
    We can associate a state and a message to our presence. The state can be one of the following (names can change depending on the client):
    • available (default): you’re online.
    • away: you’re away for a short period
    • chat: you want to talk
    • dnd (do not disturb): you’re occupied (often called “busy” in clients)
    • xa (eXtended Away): you’re away for a long while.
    The status messages allow you to specify your availability in a clear language (for example: “I’m watching a movie, do not disturb”), even though, in practice, it is used for any kind of message (a lot of people use a quote, for example).
  • <message/> A message’s sending of type “send and forget”. There are 5 types of messages::
    • chat: the most well-known message, used for simple instant messaging;
    • error: this one is usually managed directly by client software. It is often shown by means of a notification window in your client, indicating that something wrong occurred;
    • groupchat: as “chat”, but for discussion with multiple people. In practice the difference concerns only developers and it should be transparent in the client;
    • headline: an important message, an announcement. Normally, these messages aren’t kept offline, so if you aren’t connected while the message is sent, you shouldn’t receive it. These messages don’t expect answers. A typical example is an announcement for an imminent server maintenance;
    • normal: a little known yet interesting type. It is a message which generally has a subject, but outside of an instant conversation. Yes, exactly like an email! It is more or less its XMPP equivalent.
    Conversation threads are managed as well, but we’ll talk about it another time.
  • <IQ/> (Info/Query): used for everything that works on a question/answer pattern (it is mandatory to provide an answer to an request, even if you need to reply with an error). This is used mainly by developers, as it serves as a basis for most of the features you need. Using it is like saying "I need to know or edit this information".
 
I don't want to delve into technical details, but it seems essential for a user to know different message and presence types to understand their client.
 
One should note that there is an excellent feature that is largely underused in XMPP: it natively knows how to handle different languages because of its inheritance from XML (xml:lang). In other words, you can specify a normal or status message in French, German and Slovak at the same time. This is a major asset that we intend to use in Libervia.
 
Now let's talk about another essential part: the contact list.
 
It is called "roster" in the XMPP world. You can assign 0, 1 or several groups ("family", "friends", etc.), a name (which is an alias chosen by yourself, not by your contact), and subscription information to every contact you add to your roster.
 
Subscription lets you know whether you have allowed your contact to see your presence information and whether you are allowed to see theirs. Therefore, every time someone adds you to their contact list, your client (e.g. Gajim) asks you whether you wish to grant them access to your presence information. Note that these permissions don't need to be symmetrical: a contact may have been allowed to see your contact information without enabling you to see theirs, and vice versa. It might even be possible that neither of you can see each other's presence information (but I think most clients remove the contact from the roster in that case).
 
Groups are dependent on contacts, not the other way around (it's not a list of groups which contains the contacts): this explains why having an empty group (i.e. without any contact) isn't possible. In my opinion, groups too are underused in the XMPP world, but we'll get back to this.
 
 
That's it for today. I opted to keep the part on extensions for the next post to keep this one lighter.

Let's talk XMPP - episode 1 - the basics

This article was initially published in French, and it got some interest, so we started to translate the whole series in English. If you can read French, you can follow the whole series there: http://www.goffi.org/tag/parlons_xmpp


The translation to English was done thanks to: Poulet, Éfrit, Paco and mbarbarosa. The whole series is under CC By-SA, and any help would be appreciated to help with the translation of next articles.

G'day,
 
Well, as it’s a shame that XMPP is not well known or understood, I decided to start a series of articles to explain what it is.
 
These articles are for a technical audience, but not necessarily for developers, and I hope it will help you to understand the advantages of this protocol and to use your software in a better way.
 
Being a developer of the “Salut à Toi” project, I’ll probably give examples with it quite often.
 
So let’s start with basis.
 
What’s XMPP? It’s a standard message and presence protocol, and extensible (XMPP means « eXtensible Message and Presence Protocol », that is it’s documented and used as a reference (validated by standards organization: the IETF). It allows all software which use it to speak the same language, and so to be interoperable. It’s a libre protocol, that is you can get the documentation and use it for free, without any legal or technical restrictions, and you can improve or modify it (but if you divert and don’t suggest your modifications, you risk to lose the compatibility with other software).
 
XMPP is decentralized and federated, that is you can have servers anywhere, they could (if they don’t forbid it explicitly in their configuration) communicate with each other.
 
It’s a popular protocol, many software allow to use it: for servers, there are Prosody, Ejabberd, Openfire, Tigase, Mongooselm, Metronome, etc. For clients: Gajim, Poezio, Pidgin, Psi, Swift, Jappix, Movim and of course Libervia/Salut à Toi (I let you find the official websites by yourself). A complete list (servers, clients and libraries) is available here: https://xmpp.org/xmpp-software/.
 
If you cannot install your server at home, many public ones are available: in France one can cite those of APINC ((jabber.fr, im.apinc.org, etc), of the Quadrature du Net, etc. A small list (it’s not up-to-date, don’t hesitate to contribute) is available here in French,, if not you can check on https://xmpp.net/directory.php or http://www.jabberes.org/servers (yes, there are a lot!). But I strongly suggest you to install your own server or to go meet a local organization that you can contact easily: on the one hand if you install it by yourself you’ll have a better control on your own data and on the other hand if you want a specific feature you’ll be able to ask admins for an update.
 
Knowing all that, let’s try to install an account.
 
Once the server installed or a public server chosen, you can create an account. You’ll have then an address, a “JID” (Jabber ID, “Jabber” is the former name of the protocol, this name is now owned by a private company and is kept here for historical reasons).
 
This address is on the form of local_name@domain.tld/resource, or in canonical form (or what is called “bare JID”) local_name@domain.tld. For example, mine is goffi@jabber.fr. Does it sound familiar? Yes, it really looks like email addresses!
 
So what is this resource? The resource is linked with the client software that you use to connect: XMPP has been designed from the beginning to allow several clients to connect at once (10 years ago, a few messaging protocols were able to do that, and connecting again from a different place was often resulting in the disconnection of the first client) and this resource is used to identify them. In other words, you have a resource only once connected, and it will be a different one for each client that you are using: if I connect with Libervia, Gajim and Movim, I’ll have 3 different resources.
 
It used to be several strategies to name the resource, sometimes it was used to show the connection location (“home”, “work”), clients often used their names as default value (“gajim”, “psi”). Today, it’s well accepted that it’s better to have a resource that we cannot guess, as somebody can know if you are online or not (even if you don’t want this information to be public) by doing a request to this resource. The best way is to let the server choose the resource for you.
 
Finally, the resource is linked with a priority: it allows to indicate, if several resources are available, which one will get the message. But we’ll see that later.
 
In the next episode, I'll talk about extensions an features discovery
 
That’s it. Let me know if you are interested in this series, if it seems too technical for you, or if you have any comment or fix to suggest. Everything is under the license CC By-SA, so don't hesitate to re-use, share or modify !
Powered by Salut à Toi
Subscribe to this news feed Atom feed