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[gsoc] osc2 client – summary of week 3 and 4

June 19th, 2012 by

Hi,

here’s a small summary of the 3rd and 4th (coding) week . First of all I
wasn’t able to do lots of work in week 3 and 4 so I’m still working on
the new build module for the osc2 library.
The initial plan was to copy/reuse some of the existing modules from the
(old) “osc” like the cpio [1] and packagequery modules. But I decided to
refactor/rewrite cpio module for the following reasons:

  • “save” disc space:
    In our scenario we retrieve a cpio archive from the api (which contains
    binary packages for example). The old cpio module expects a filename
    in order to “unpack” the archive – that is the file has to be stored on
    disc first. Consequently approximately 2 * of free disc
    space is needed.
    The new idea is that we pass a file-like object (in our case an object
    which inherits from “AbstractHTTPResponse”) to the cpio module and
    unpack the archive “on the fly” (without storing the http response
    on disc first).
  • have testcases:
    The old cpio module has no testcases (because some time ago I didn’t
    follow the TDD approach;) ). For nearly all modules in osc2 there exist
    testcases (white-box tests) thus it would be nice if we have some
    testcases for the cpio module, too (theoretically we could add some
    black-box tests (the current methods aren’t really testable thus
    white-box tests aren’t possible)).
  • have a nice pythonic interface:
    The new interface will look like this:

    from cpio import cpio_open
    # let "f" be a file-like object (for instance a http response)
    with cpio_open(fobj=f) as cpio_archive:
        for a_file in cpio_archive:
            # store file (with correct permissions etc.) in os.curdir
            a_file.write(os.curdir)
            # alternatively it's also possible to read some data (instead of
            # writing it to disc) via a_file.read(len)

    We will also support a plain filename in cpio_open.

Currently the cpio module will only support the “new ascii” (ascii SVR4
no CRC) format and regular files (that’s sufficient for our needs). But
it will be possible to simply pass in a class for a different format
(that is no code has to be altered in order to support a new format).

Finally this will be finished by the end of this week.
If you have any questions or suggestions please tell me:)

Marcus

[1] https://github.com/openSUSE/osc/blob/master/osc/util/cpio.py

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