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

[Daniel P. Berrange]

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.

Regards,
Daniel
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