I agree with Tomasz that there are changes that are definitely needed 
given how much technology has changed since jabberd2 was first released.

Re 1. Merging separate daemons to one.

I am not sure if merging them into one process is the best idea. It sure is
convenient, but isolation is a nice thing to have. Specially, when you
have unauthorized users hammering on C2S. To be honest, I believe, that
instead of going micro – go macro. Think distributed scalable server platform
rather than ease of running on one machine. In today’s services oriented world,
this approach will find a better home I believe. Which brings me to router. 
Today, it’s a bottleneck. There are several ways, as mentioned in Tomasz’s 
email, to fix this issue and something that would be great to tackle this as
part of this re-architecture. MoongooseIM is a good place to look at for
scalable XMPP platform architecture.

4. Configuration interface

Subscription based model works well and its okay to force developers
to write config change handlers. It’s 2016, time to not argue about this
point given the advantages.

5. JavaScript support.

Personally, C/C++ is fine, however, if folks insist, would be good to keep
the existing setup and allow for JS SM components as a compile
time option.

6. String handling

Something that would be nice to see is allowing SM modules or others
to pre-process the PKT to extract as much meaningful data once (in the
beginning) and then passing that object around. Currently, at each
stage of the SM module call chain, we have to re-process the PKT or NAD
to extract the same data over and over again. Unnecessary work that 
can be avoided easily. Easy to do in C++ but a bit awkward in C.

On 5/30/16, 1:31 AM, "Tomasz Sterna" <to...@xiaoka.com> wrote:

>There are some things we already talked about on Gitter channel [1],
>but I would like to raise them on the ML for peer review.
>As you can see from late activity, jabberd2 project is far from dead.
>With the inclusion of new features like WebSocket support, C99 code
>compatibility, IPv6 improvements, modern TLS handling, SASL Anonymous,
>password hashing, CRAM-MD5 and more... it is not a stale codebase
>But it is far from modern too...
>There are some changes I would like to introduce in the near future and
>I would like to hear your thoughts about:
>1. Merging separate daemons to one.
>Current design of jabberd2 with separate router, sm, c2s, s2s processes
>is designed to allow nice separation of concerns and distribution of
>processing. Separate processes are proved to be better approach than
>threads too.
>But most installations of jabberd are not distributed, with one
>instance of each component. Especially when c2s and sm got vhost
>support and are able to handle more than one domain.
>Also, modern OS architectures are tuned for event processing rather
>than multithreading, so event based architecture is better suited for
>them. Even jabberd2 process internally is event based on MIO.
>So, it makes sense to allow for running all component instances in one
>process, especially on amateur, low load servers.
>Merging processes will allow for having one main loop only, so
>maintaining bugfixes in it will be easier (main.c of all processes is a
>copy-paste, with all the bugs, so bugs are also multiplied).
>2. Phasing out MIO.
>This is closely related to above. MIO used by jabberd2 does not have
>clerar main loop support, which is implemented separately in each
>component main.c and is hardly pluggable.
>Also, the way MIO is implemented (in .h file, with platform specific
>bits in .c) makes it a maintanance nightmare.
>I would really like to replace it with a modern, upstream maintained
>event library. The nicest one I know is libuv, which also gives us nice
>platform independence layer.
>I already have a working c2s port to libuv as a PoC.
>3. Phasing out router.
>router component is the one binding all the others.
>In current design it is the single point of failure. Other components
>already support multiple instances, but router proved to be difficult
>to multiply.
>The most radical, yet compelling solution to this problem is getting
>rid of the router at all. There are many cooked solutions for local
>packet distribution, which Local Message Bus [2] looks like most
>promising solution. I would see either Mbus [3] or NN_BUS [4] taking
>role of router component.
>The added advantage of using a Message Bus is the ability to connect to
>the bus with alternative implementations to perform own actions.
>i.e. having the ability to use CLI tools to eavesdrop and send messages
>to the bus proved to be priceless when I implemented a PoC of the Bus
>in experimental jabberd branch.
>Bus also solves the problem of distribution - it is up to the
>deployment administrator whether one sets up local, one-machine only
>bus or a network distributed one.
>4. Configuration interface.
>A the moment jabberd is configured with static XML files loaded at
>daemon startup. It is close to impossible to change the values in
>runtime, as random places of the process are using copies of values or
>direct pointers to values from config structure.
>This heavily impedes implementation of features such as XEP-0133
>Service Administration or Web interface.
>From my experience, the best handling of such requirements is to
>provide write-only/change-subscribe interface similar to GConf/dconf.
>This interface does not allow reading on-demand of random values, but
>allows only subscription to change and write-value + publish change.
>This approach forces programmer to write value-change handlers in
>application code, which allows changing the value by anyone at any
>Do you know any standalone library that implements such approach,
>or do I need to implement custom solution in jabberd codebase?
>5. JavaScript support.
>Let's face it - JavaScript is all the hype today :-) It also is a very
>good language for data processing. I think it would be a good solution
>for implementation of modern XEP logic in sm component.
>sm is implemented in C with all RFC required logic, and all XEPs are
>loadable modules to sm and these add JEP/XEP functionality.
>Having an option to implement XEP logic in JS instead of plain C,
>should speed up recent and experimental XEP adoption in jabberd.
>This gives concerns to jabberd2 as an embedded server though - current
>jabberd2 is perfectly able to work fine on low resource machines such
>as DD-WRT router. Introducing heavy JS JIT machine could change that.
>But with the raise of fast, embeddable JavaScript interpreters like
>Duktape [5] it should be non-issue.
>6. Proper logging.
>jabberd2 has two logging facilities: log and debug_log, with log
>logging only most interesting events and debug_log all the rest.
>To aid debugging issues with your deployment you may enable -D switch
>or send SIGUSR2 to your demon. But this will flood you with all the
>debug and trace information, only programmers can make us off.
>I am already working on replacing the logging with more fine-tuned
>log4c [6] implementation.
>7. DBI interface to RDBM.
>sm storage backends for SQL RDBMs are a copy-pasted clones of the same
>implementation sprinkled with improvements here and bugfixes there.
>Porting new features and fixes between backends is painful and
>unnecessary. I would rather see one backend for all these - it's SQL
>after all.
>I plan on merging all SQL storage backends to one, libdbi [7] based one
>merging all the features and fixes, pushing all the discrepancies of
>RDBMs to libdbi-drivers upstream implementation. Then slowply phasing
>out individual implementations.
>8. String handling.
>Every seasoned programmer knows that C "strings" are not Strings.
>char* is not a String. String is a sequence of characters of known
>length. char[] comes close, but it immediately degrades to char*.
>Also, contrary to its name, char is not a character. Characters are
>coded with natural numbers and char is signed. Also, UTF-8 encoding
>(the only one we care about) does not fit in 8bits of char.
>To mitigate these issues I am in the process of introducing sds [8]
>and libunistring [9] for all string handling.
>What do you think of these ideas, guys?
>Do you have any suggestions for even more disturbing improvements? :-)
>I would love to hear all feedback.
>You may take a look at experimental/PoC codebase at ashnazg [10] branch on 
>[1] http://gitter.im/jabberd2/jabberd2
>[2] http://en.wikipedia.org/wiki/Message-oriented_middleware
>[3] http://www.mbus.org/
>[4] http://nanomsg.org/v0.9/nn_bus.7.html
>[5] http://duktape.org/
>[6] http://log4c.sourceforge.net/
>[7] http://libdbi.sourceforge.net/
>[8] http://github.com/antirez/sds
>[9] http://www.gnu.org/software/libunistring/
>[10] http://github.com/jabberd2/jabberd2/tree/ashnazg
> /o__ 
>(_<^' Aim for the moon. If you miss, you may hit a star.

Reply via email to