[Pulp-dev] pulp_rpm and The Pitfalls of urljoin()

Grant Gainey ggainey at redhat.com
Mon Mar 15 19:43:17 UTC 2021

Hey folks,

I was looking at https://pulp.plan.io/issues/7995 with an eye to fixing it
for 3.12. The underlying problem can be summed up as "urljoin doesn't do
what you expect if 'base' doesn't end in a '/'"[0][1]. Using urljoin() as
if all it does is "concatenate these two strings with a '/' between them"
is a pretty common misuse that works 'most of the time', alas.

Looking around to see if we do this anywhere else, I find that pulp_rpm
uses urljoin() in a number of places that I think might be subject to the
same unintended problem. However, the semantics of sync'ing RPM
repositories is even *more* nuanced than urljoin()'s is!

I am tempted to replace urljoin() with just straightforward path-creation.
Here's the list of places in pulp_rpm non-test python that uses it

(pulp3) (master) ~/github/Pulp3/pulp_rpm $ find . -name \*.py | grep -v
tests | xargs grep -n "urljoin("
./pulp_rpm/app/kickstart/treeinfo.py:23:            url=urljoin(remote_url,
namespace), silence_errors_for_response_status_codes={403, 404}
./pulp_rpm/app/models/repository.py:355:                gpgkey_path =
./pulp_rpm/app/models/repository.py:358:                gpgkey_path =
urllib.parse.urljoin(gpgkey_path, self.base_path, True)
./pulp_rpm/app/tasks/synchronizing.py:101:    downloader =
remote.get_downloader(url=urljoin(url, "repodata/repomd.xml"))
./pulp_rpm/app/tasks/synchronizing.py:138:    downloader =
remote.get_downloader(url=urljoin(remote_url, "repodata/repomd.xml"))
./pulp_rpm/app/tasks/synchronizing.py:243:            new_url =
urljoin(remote_url, path)
 url=urljoin(self.data.remote_url, "repodata/repomd.xml")
 url=urljoin(self.data.remote_url, self.treeinfo["filename"]),
 url=urljoin(self.data.remote_url, path),
./pulp_rpm/app/tasks/synchronizing.py:599:                url =
urljoin(self.data.remote_url, package.location_href)
./pulp_rpm/app/tasks/synchronizing.py:722:        repodata_url =
urljoin(self.data.remote_url, record.location_href)
./pulp_rpm/app/tasks/synchronizing.py:726:        self.data.updateinfo_url
= urljoin(self.data.remote_url, record.location_href)
./pulp_rpm/app/tasks/synchronizing.py:731:        comps_url =
urljoin(self.data.remote_url, record.location_href)
./pulp_rpm/app/tasks/synchronizing.py:735:        self.data.modules_url =
urljoin(self.data.remote_url, record.location_href)
 url=urljoin(self.data.remote_url, record.location_href),
./pulp_rpm/app/downloaders.py:84:            url = urljoin(self.url,
(pulp3) (master) ~/github/Pulp3/pulp_rpm $

Any thoughts before I dive down this rabbithole? I'm afraid I don't even
have a pocketwatch...


[0] https://docs.python.org/2/library/urlparse.html#urlparse.urljoin
[1] https://stackoverflow.com/a/10893427
Grant Gainey
Principal Software Engineer, Red Hat System Management Engineering
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