[FS#361] git: add pre-receive hook to reject commits without SoB line

[LEDE Bugs]

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FS#361 - git: add pre-receive hook to reject commits without SoB line
User who did this: Stijn Tintel (stintel)
Task details edited:
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I recently pushed a commit without Signed-off-by. Looking at the git history, this happened before.
To avoid this in the future, add a pre-receive that checks for signed-off-by line, and rejects the push when it's not found.

Here is some (ugly) example python code that does this, and even goes 1 step further: it rejects the push if there is any commit that does not contain a SoB for the commit author. I think it makes sense to enforce this, it came up in https://github.com/lede-project/source/pull/592#issuecomment-265760007 .


author = ""
for line in sys.stdin:
    (base, commit, ref) = line.strip().split()
    diff = subprocess.Popen(['git', 'log', '-n 1', commit],stdout=subprocess.PIPE)
    for line in iter(diff.stdout.readline, ''):
        if line.startswith('Author: '):
            author = re.sub('^Author: ', '', line)
            print('Found author: {}').format(author)
            continue
        if line.find('Signed-off-by: '):
            sob = re.sub('.*Signed-off-by: ', '', line)
            if sob == author:
                print('Found SoB line for author')
                return True

sys.exit(1)

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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=361