[OPEN-ILS-DEV] OpenSRF 101

[Michael J. Giarlo]

Thanks a bunch, Dan; my test Python service is now running.  Thanks
also to Jeff, who replied with much the same suggestions on my gist.

Some notes below.

On Sat, Oct 30, 2010 at 03:59, Dan Scott <dan at coffeecode.net> wrote:
>
> First up: your config settings look pretty good to me. Bravo! One thing
> to point out, though, is that the Python service needs to be implemented
> as a module available from sys.path, and the name of the module is what
> you need to specify as the content of the <implementation> element in
> the application config section. So I copied osrf_reverse.py to
> /usr/lib/python2.6/site-packages/. and changed
> <implementation>osrf.test</implementation> to
> <implementation>osrf_reverse</implementation>

Aha, that makes sense.  What I did:

 * Added an /opensrf/lib/python directory
 * Symlinked my osrf_test.py from /opensrf/lib/python into my
workspace, so I can continue coding in my usual place
 * Pulled opensrf.py from the source into /opensrf/bin
 * Tweaked opensrf.py's default path by adding:
    sys.path.append(os.path.join(os.path.dirname(__file__), "lib", "python"))

> Second: to start the Python service, you don't run it directly; instead,
> you use the Python controller script to run it (similar to how
> osrf_ctl.sh invokes opensrf-perl.pl to start the Perl services). This
> controller script can be found in src/python/opensrf.py - we don't
> install it into /openils/bin/ yet because nobody was using Python in
> OpenSRF yet - so let's give it a shot with the following (using "-l"
> assuming that we're pointing to the "<localhost>" set of services) as
> the opensrf user:

Great.  I also tweaked osrf_ctl.sh to hook into opensrf.py.

Then I noticed some odd behavior re what's returned via
osrf.set.get('apps').  One key returned in the dict is "#comments",
which does not contain the 'language' key, so a KeyError exception is
raised.  Fixed that with the following diff in opensrf.py:

114c112
<         if isinstance(svc, dict) and 'language' in svc and
svc['language'] == 'python':
---
>         if isinstance(svc, dict) and svc['language'] == 'python':


> ... this is a painful Python DNS issue that is fortunately nicely
> documented in the OpenSRF README - see "dnsmasq".

I did indeed run into this, and the stuff in the README worked
brilliantly.  Huzzah for good documentation!

> YAY! Looks like an off-by-one error on the "n" but
> otherwise that's what we want.

Yep.  Simplified my reverse_text method to a one liner:

    request.respond(message[::-1])

No more off-by-one.

> However, given an actual user of this
> code, I'll be happy to put some energy into refining the packaging to
> (for example) get opensrf.py installed if people choose --enable-python,
> provide some more examples / test cases, put together some docs, etc.

It's early days yet, but I can see the potential in using OpenSRF for
what we're about to start prototyping at Penn State.  If so, we're
pretty gung ho about Python, so we're likely to cross paths again,
i.e., I think we can help you help us.

Thanks again, Dan & Jeff!

-Mike

P.S. Here are the osrf_ctl.sh diffs, trivial though they are:

51,53d50
<     start_python
<     stop_python
<     restart_python
159,179d155
< start_python() {
<     echo "Starting OpenSRF Python";
<     OPT_LOCAL=""
<     if [ "$OSRF_HOSTNAME" = "localhost" ]; then
< 	OPT_LOCAL="-l"
<     fi
<     opensrf.py -d -p $OPT_PID_DIR -f $OPT_CONFIG -a start_all $OPT_LOCAL
<     return 0;
< }
<
< stop_python() {
<     echo "Stopping OpenSRF Python";
<     OPT_LOCAL=""
<     if [ "$OSRF_HOSTNAME" = "localhost" ]; then
< 	OPT_LOCAL="-l"
<     fi
<     opensrf.py -p $OPT_PID_DIR -f $OPT_CONFIG -a stop_all $OPT_LOCAL
<     sleep 1;
<     return 0;
< }
<
223,225d198
< 	"start_python") start_python;;
< 	"stop_python") stop_python;;
< 	"restart_python") stop_python; start_python;;
229,234c202,207
< 	"start_osrf") start_perl; start_c; start_python;;
< 	"stop_osrf") stop_perl; stop_c; start_python;;
< 	"restart_osrf") stop_perl; stop_c; stop_python; start_perl;
start_c; start_python;;
< 	"stop_all") stop_c; stop_perl; stop_python; stop_router;;
< 	"start_all") start_router; start_perl; start_c; start_python;;
< 	"restart_all") stop_c; stop_perl; stop_python; stop_router;
start_router; start_perl; start_c; start_python;;
---
> 	"start_osrf") start_perl; start_c;;
> 	"stop_osrf") stop_perl; stop_c;;
> 	"restart_osrf") stop_perl; stop_c; start_perl; start_c;;
> 	"stop_all") stop_c; stop_perl; stop_router;;
> 	"start_all") start_router; start_perl; start_c;;
> 	"restart_all") stop_c; stop_perl; stop_router; start_router; start_perl; start_c;;