[Voiceglue] Audio caching

[Doug Campbell]

> EROR SNDCACHE foo.bar 
> /var/lib/asterisk/sounds/voiceglue/url/foo.bar.co.uk/media/_bar_session:bf7277c8a416ea3ce18be97ef45ee909/main_menu.wav.tmp 
> <http://foo.bar.co.uk/media/_bar_session:bf7277c8a416ea3ce18be97ef45ee909/main_menu.wav.tmp> 
> file has bad stat: No such file or directory

This gets reported when curl was instructed to retrieve the content, but
no content was retrieved.  You may want to try running curl manually on
that audio file URL to see if there is an issue with it.

Otherwise, a small code example and/or a full debug log would help
track down what's going on here.

> I can see the actual wav file has been cached but I don't know why 
> voiceglue is looking for a wav.tmp file - which isn't there.

Voiceglue is using curl to verify that the content hasn't changed
since the audio got cached.  It requests the audio URL again to
either get the new content, or get a 304 (Not Modified) response.
Because this error was generated, it means voiceglue did not find
a 304 response, which means the content is changed, and should have
been downloaded into the .wav.tmp file.  Perhaps there is some error
in recognition of the 304 response.

> I've tried 
> to switch caching off completely using audio_maxage = 0, but that 
> results in a parsing error.

Yes, the code prohibits setting that to 0.
I fixed that for the next release.  However,
that won't change the issue here, as it will
continue to try to re-verify the audio.

Doug Campbell