remove docs folder
* mission statement is now hosted on https://gultsch.de * XEPs.md has been replaced by conversations.doap * observations.md is just outdated and boring by now
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Daniel Gultsch
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Conversations is a messenger for the next decade. Based on already established
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internet standards that have been around for over ten years Conversations isn’t
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trying to replace current commercial messengers. It will simply outlive them.
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Commercial, closed source products are coming and going. 15 years ago we had ICQ
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which was replaced by Skype. MySpace was replaced by Facebook. WhatsApp and
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Hangouts will disappear soon. Internet standards however stick around. People
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are still using IRC and e-mail even though these protocols have been around for
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decades. Utilizing proven standards doesn’t mean one can not evolve. GMail has
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revolutionized the way we look at e-mail. Firefox and Chrome have changed the
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way we use the Web. Conversations will change the way we look at instant
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messaging. Being less obtrusive than a telephone call instant messaging has
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always played an important role in modern society. Conversations will show that
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instant messaging can be fast, reliable and private. Conversations will not
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force its security and privacy aspects upon the user. For those willing to use
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encryption Conversations will make it as uncomplicated as possible. However
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Conversations is aware that end-to-end encryption by the very principle isn’t
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trivial. Instead of trying the impossible and making encryption easier than
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comparing a fingerprint Conversations will try to educate the willing user and
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explain the necessary steps and the reasons behind them. Those unwilling to
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learn about encryption will still be protected by the design principals of
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Conversations. Conversations will simply not share or generate certain
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information for example by encouraging the use of federated servers.
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Conversations will always utilize the best available standards for encryption
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and media encoding instead of reinventing the wheel. However it isn’t afraid to
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break with behavior patterns that have been proven ineffective.
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32
docs/XEPs.md
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docs/XEPs.md
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* XEP-0027: Current Jabber OpenPGP Usage
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* XEP-0030: Service Discovery
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* XEP-0045: Multi-User Chat
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* XEP-0048: Bookmarks
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* XEP-0084: User Avatar
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* XEP-0085: Chat State Notifications
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* XEP-0092: Software Version
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* XEP-0115: Entity Capabilities
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* XEP-0163: Personal Eventing Protocol (avatars and nicks)
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* XEP-0166: Jingle (only used for file transfer)
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* XEP-0172: User Nickname
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* XEP-0184: Message Delivery Receipts (reply only)
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* XEP-0191: Blocking command
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* XEP-0198: Stream Management
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* XEP-0199: XMPP Ping
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* XEP-0234: Jingle File Transfer
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* XEP-0237: Roster Versioning
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* XEP-0245: The /me Command
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* XEP-0249: Direct MUC Invitations (receiving only)
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* XEP-0260: Jingle SOCKS5 Bytestreams Transport Method
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* XEP-0261: Jingle In-Band Bytestreams Transport Method
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* XEP-0280: Message Carbons
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* XEP-0308: Last Message Correction
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* XEP-0313: Message Archive Management
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* XEP-0319: Last User Interaction in Presence
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* XEP-0333: Chat Markers
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* XEP-0352: Client State Indication
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* XEP-0357: Push Notifications
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* XEP-0363: HTTP File Upload
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* XEP-0368: SRV records for XMPP over TLS
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* XEP-0377: Spam Reporting
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* XEP-0384: OMEMO Encryption
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Observations on implementing XMPP
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=================================
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After spending the last two and a half month basically writing my own XMPP
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library from scratch I decided to share some of the observations I made in the
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process. In part this article can be seen as a response to a blog post made by
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Dr. Ing. Georg Lukas. The blog post introduces a couple of XEP (XMPP Extensions)
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which make the life on mobile devices a lot easier but states that they are
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currently very few implementations of those XEPs. So I went ahead and
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implemented all of them in my Android XMPP client.
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### General observations
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The first thing I noticed is that XMPP is actually okish designed. If you were
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to design a new chat protocol today you probably wouldn’t choose XML again
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however the protocol basically consists of only three different packages which
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are quickly hidden under some sort of abstraction layer within your library.
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Getting from zero to sending messages to other users actually was very simple
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and straight forward. But then came the XEPs.
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### Multi-User Chat
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The first one was XEP-0045 Multi-User Chat. This is the one XEP of the XEPs I’m
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going to mention in my article which is actually wildly adopted. Most clients
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and servers I know of support MUC. However the level of completeness varies.
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MUC actually introduces access and permission roles which are far more complex
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than what some of us are used to from IRC but a lot of clients just don’t
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implement them. I’m not implementing them myself (at least for now) because I
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somewhat doubt that someone would actually use them (however this might be some
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sort of chicken or egg problem). I did find some strange bugs though which might
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be interesting for other library developers. In theory a MUC server
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implementation can allow a single user (same jid) to join a conference room
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multiple times with the same nick from different clients. This means if someone
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wants to participate in a conference from two different devices (mobile and
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desktop for example) one wouldn’t have to name oneself `userDesktop` and
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`userMobile` but just `user`. Both ejabberd and prosody support this but with
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strange side effects. Prosody for example doesn’t allow a user to change its
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name once two clients are “merged” by having the same nick.
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### Carbons and Stream Management
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Two of the other XEPs Lukas mentions — Carbons (XEP-0280) and Stream Management
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(XEP-0198) — were actually fairly easy to implement. The only challenges were to
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find a server to support them (I ended up running my own Prosody server) and a
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desktop client to test them with. For carbons there is a patched Mcabber version
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and Gajim. After implementing stream management I had very good results on my
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mobile device. I had sessions running for up to 24 hours with a walking outside,
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loosing mobile coverage for a few minutes and so on. The only limitation was
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that I had to keep on developing and reinstalling my app.
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### Off the record
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And then came OTR... This is were I spend the most time debugging stuff and
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trying to get things right and compatible with other clients. This is the part
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were I want to help other developers not to make the same mistakes and maybe
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come to some sort of consent among XMPP developers to ultimately increase the
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interoperability. OTR has some down sides which make it difficult or at times
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even dangerous to implement within XMPP. First of all it is a synchronous
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protocol which is tunneled through a different protocol (XMPP). Synchronous
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means — among other things — auto replies. (An OTR session begins with “hi I’m
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speaking otr give me your key” “ok cool here is my key”) And auto replies — we
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know that since the first time an out of office auto responder went postal — are
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dangerous. Things really start to get messy when you use one of the best
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features of XMPP — multiple clients. The way XMPP works is that clients are
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encouraged to send their messages to the raw jid and let the server decide what
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full jid the messages are routed to. If in doubt even all of them. So what
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happens when Alice sends a start-otr-message to Bobs raw jid? Bob receives the
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message on his notebook as well as his cell phone. Both of them answer. Alice
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gets two different replies. Shit explodes. Even if Alice sends the message to
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bob/notebook chances are that Bob has carbon messages enabled and still receives
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the messages on both devices. Now assuming that Bobs client is clever enough not
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to auto reply to carbonated messages Bob/cellphone will still end up with a lot
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of garbage messages. (Essentially the entire conversation between Alice and
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Bob/notebook but unreadable of course) Therefor it should be good practice to
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tag OTR messages as both private and no-copy (private is part of the carbons
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XEP, no-copy is a general hint). I found that prosody for some reasons doesn’t
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honor the private tag on outgoing messages. While this is easily fixed I presume
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that having both the private and the no-copy tag will make it more compatible
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with servers or clients I don’t know about yet.
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#### Rules to follow when implementing OTR
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To summarize my observations on implementing OTR in XMPP let me make the
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following three statements.
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1. While it is good practice for unencrypted messages to be send to the raw jid
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and have the receiving server or user decide how they should be routed OTR
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messages must be send to a specific resource. To make this work the user should
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be given the option to select the presence (which can be assisted with some
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educated guessing by the client based on previous messages). Furthermore a
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client should encourage a user to choose meaningful presences instead of the
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clients name or even random ones. Something like `/mobile`, `/notebook`,
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`/desktop` is a greater assist to any one who wants to start an otr session then
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`/Gajim`, `/mcabber` or `/pidgin`.
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2. Messages should be tagged private and no-copy to avoid unnecessary traffic or
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otr error loops with faulty clients. This tagging should be done even if your
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own client doesn’t support carbons.
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3. When dealing with “legacy clients” — meaning clients which don’t follow my
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advise — a client should be extra careful not to create message loops. This
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means to not respond with otr errors if a client is not 100% sure it is the only
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client which received the message
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