[Ur] Collecting Ur/Web examples

[Adam Chlipala]

On 05/07/2014 05:17 AM, Sergey Mironov wrote:
> Hi! I use UrWeb as a part of build-server engine. The server will be
> used to build and deploy a firmware updates to network routers. In
> more details, It's task is to 1) authenticate user 2) Figure out
> whether they need a software update by comparing effective firmware
> version against the latest one 3) Launch the build process if needed
> and store the firmware path to a database 4) Serve the firmware which
> is a ~20M encrypted tarball.
>
> The project as a whole is a closed source project, but I think I'll be
> allowed to officially open the UrWeb part.

Sounds like a fun example to be able to cite!  I'll be grateful if you 
can indeed release the Ur/Web part open-source in the next month or so.

> I've checked the urweb-callback against the new version of the UrWeb.
> Unfortunately, urweb-callback fails to pass the stress test with your
> version of uw_commit. The symptom is a 'job leak' - several jobs are
> not freed at the end of the test. At first glance your version is
> quite similar to mine, but probably there is a critical difference
> hiding somewhere.  I'll try to figure out what is going on.

Thanks!  I can also look at it again (though maybe not right away), 
which is easier if I have a representative part of your code.

> I also thought about potential application of the UrWeb in embedded
> web applications. The strong memory guarantees and C output of the
> compiler make it possible to compile the good server for ARM cpus
> which is a big advantage comparing to Haskell and Lisp frameworks.
> (I've read that Haskell works for arm nowdays) I wish I have some time
> to build a demo project for RaspberryPI or other popular arm board.

I don't know if anyone has built Ur/Web servers for ARM, but I can't 
think of any reason why it wouldn't work right away.  If there are 
issues, they're probably easy to fix.  Certainly Ur/Web is used 
regularly with both 32-bit and 64-bit x86.

> The important thing here is the database. Postgres and MySql are often
> too heavy choice for such applications so the sqlite may probably be a
> backend of choice. We may need to improve the sqlite compatibility in
> order to go embedded.

I'm not aware of any SQLite incompatibility, but there may also have 
been less testing with this backend than with the others.