On Mon, Feb 23, 2015 at 8:24 PM, Paul Moore <p.f.moore@gmail.com> wrote:

On 23 February 2015 at 19:01, Daniel Holth <dholth@gmail.com> wrote:
> Sounds reasonable. It could be done by just reading the entire file
> contents after the shebang and re-writing them with the necessary
> offset all in RAM, truncating the file if necessary, without involving
> the zipfile module very much; the shebang could have some amount of
> padding by default; the file could just be re-compressed in memory
> depending on your appetite for complexity.

The biggest problem with that is finding the end of the prefix data.
Frankly it's easier just to write a new prefix then use the zipfile
module to rewrite all of the content. That's what the current code
does writing to a new file.

I don't think you need to rewrite all of the contents, if you don't mind poking into zipfile internals:

endrec = zipfile._EndRecData(f)

prefix_length = endrec[zipfile._ECD_LOCATION] - endrec[zipfile._ECD_SIZE] - endrec[zipfile._ECD_OFFSET]

I do something similar to get at the prefix, although I need the zipfile opened anyway, so I use:

endrec = zipfile._EndRecData(f) # pylint: disable=protected-access

zf = zipfile.ZipFile(f)

# endrec is None if reading it failed, but then ZipFile should have

# raised an exception...

assert endrec

prefix_len = zf.start_dir - endrec[zipfile._ECD_OFFSET] # pylint: disable=protected-access

Paul
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