Small socket problem

[Jean-Paul Calderone]

On Mon, 9 Feb 2009 09:43:36 +0000, John O'Hagan <research at johnohagan.com> wrote:
>Hi,
>
>I'm using the socket module (python 2.5) like this (where 'options' refers to
>an optparse object) to connect to the Fluidsynth program:
>
>            host = "localhost"
>            port = 9800
>            fluid = socket(AF_INET, SOCK_STREAM)
>            try:
>                fluid.connect((host, port))  #Connect if fluidsynth is running
>            except BaseException:
>                print "Connecting to fluidsynth..." #Or start fluidsynth
>                soundfont =  options.soundfont
>                driver = options.driver
>                Popen(["fluidsynth", "-i", "-s", "-g", "0.5",
>                "-C", "1",  "-R", "1", "-l", "-a", driver, "-j", soundfont])
>                timeout = 50
>                while 1:
>                    timeout -= 1
>                    if timeout == 0:
>                        print "Problem with fluidsynth: switching to synth."
>                        play_method = "synth"
>                        break
>                    try:
>                        fluid.connect((host, port))
>                    except BaseException:
>                        sleep(0.05)
>                        continue
>                    else:
>                        break
>
>(I'm using BaseException because I haven't been able to discover what
>exception class[es] socket uses).
>
>The problem is that this fails to connect ( the error is "111: Connection
>refused") the first time I run it after booting if fluidsynth is not already
>running, no matter how long the timeout is; after Ctrl-C'ing out of the
>program, all subsequent attempts succeed. Note that fluidsynth need not be
>running for a success to occur.

The most obvious problem is that you're trying to re-use a socket on which
a connection attempt has failed.  This isn't allowed and will always fail.
You must create a new socket for each connection attempt.

You might also want to consider using a higher level socket library than
the "socket" module.  The socket module exposes you to lots of very low
level details and platform-specific idiosyncrasies.  You may find that a
library like Twisted (<http://twistedmatrix.com/>) will let you write
programs with fewer bugs.

Jean-Paul