[Bug 445714] Re: [FFE] Image Store Proxy must handle compressed images

[Gustavo Niemeyer]

Martin,

Please rest assured I understand very well all of the consequences of
using one approach or the other, and opt to use one or the other
depending on specific needs.  In fact, if you look through the code
you'll see that in some cases subprocess was used.

In the case at hand I could very well have avoided it, but the fact
that:

 1) it was safe;
 2) it was a one liner;
 3) It is rarely executed; and
 4) I had very little time to implement the system

Guided me towards using this approach.

Also note that it's easy for people to get Subprocess wrong.  We should
probably implement a wrapper which implements the equivalent of
"getstatusoutput()" in a safe way.

In your example above, you actually got it pretty much right.  One
detail I'd change on it is that you pipe the error output and the
standard output into different file descriptors.  This means that if the
command run outputs error messages interleaved with normal output, the
normal output and the error output will be disjoint, and so will be hard
to interpret in a log or in the stdout.   The proper way would be to use
the option stderr=subprocess.STDOUT, so that the error can be observed
at the correct places.

Either way, I agree with you, it's a good practice to use subprocess.
Let's have more of it.

-- 
[FFE] Image Store Proxy must handle compressed images
https://bugs.launchpad.net/bugs/445714
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