[libvirt] [sandbox PATCH v4 10/21] Image: Add get_command function to Source

[Daniel P. Berrange]

On Wed, Sep 09, 2015 at 09:43:35AM +0200, Cedric Bosdonnat wrote:
> On Tue, 2015-09-08 at 17:21 +0100, Daniel P. Berrange wrote:
> > On Fri, Aug 28, 2015 at 01:47:38PM +0000, Eren Yagdiran wrote:
> > > Provide a way to know how a template can be started depending on the used source
> > > DockerSource will need to parse the topmost config file in order to find the igniter command
> > > ---
> > >  virt-sandbox-image/sources/DockerSource.py | 14 ++++++++++++++
> > >  virt-sandbox-image/sources/Source.py       |  4 ++++
> > >  2 files changed, 18 insertions(+)
> > > 
> > > diff --git a/virt-sandbox-image/sources/DockerSource.py b/virt-sandbox-image/sources/DockerSource.py
> > > index 760ba6c..3e0362b 100644
> > > --- a/virt-sandbox-image/sources/DockerSource.py
> > > +++ b/virt-sandbox-image/sources/DockerSource.py
> > > @@ -29,6 +29,15 @@ import os
> > >  import subprocess
> > >  import shutil
> > >  
> > > +class DockerConfParser():
> > > +
> > > +    def __init__(self,jsonfile):
> > > +        with open(jsonfile) as json_file:
> > > +            self.json_data = json.load(json_file)
> > > +    def getRunCommand(self):
> > > +        cmd = self.json_data['container_config']['Cmd'][2]
> > > +        return cmd[cmd.index('"') + 1:cmd.rindex('"')]
> > 
> > In testing, I found out we should be using 'config' here
> > not 'container_config', since the latter refers to the
> > configuration used when the image was built, which is
> > subtly different from the config that is intended to be
> > used when in it deployed.
> > 
> > In particular the 'Cmd' field does not need this string
> > munging when we use 'config' instead of 'container_config'.
> > 
> > In researching this, I found out that docker also has an
> > optional 'Entrypoints' array and if both Entrypoints and
> > Cmd are specified, we should concatenate them. If the
> > user provides command line args, then should replace
> > the 'Cmd' list, but not the 'Entrypoints' list. Finally
> > some images don'pt define any 'Cmd' or 'Entrypoints' at
> > all, in which case it seems we should just try using
> > /bin/sh, in the absence of any user supplied command.
> 
> Do we really want to have a default to /bin/sh when docker is giving an
> error to the user?

Yeah, I'm not sure really.

> Error response from daemon: No command specified

I guess the error is nicer in the csae where the user  does
not have a shell inside their image

Regards,
Daniel
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