Add utility function to retrieve canonical github urls

This new code is within a new arborescence as some more code will get moved alongside in
a new commit (the new session github currently in swh.lister module).

That current code is making anonymous requests to the github api for now.

Related to T4232

swh/core/github/utils.py

+# Copyright (C) 2022  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+
+import re
+from typing import Optional
+
+import requests
+
+GITHUB_PATTERN = re.compile(r"https?://github.com/(?P<user_repo>.*)")
+
+
+def _url_github_html(user_repo: str) -> str:
+    """Given the user repo, returns the expected github html url."""
+    return f"https://github.com/{user_repo}"
+
+
+def _url_github_api(user_repo: str) -> str:
+    """Given the user_repo, returns the expected github api url."""
+    return f"https://api.github.com/repos/{user_repo}"
+
+
+def _sanitize_github_url(url: str) -> str:
+    """Sanitize github url."""
+    return url.lower().rstrip("/").rstrip(".git").rstrip("/")
+
+
+def get_canonical_github_origin_url(url: str) -> Optional[str]:
+    """Retrieve canonical github url out of an url if any or None otherwise.
+
+    This triggers an anonymous http request to the github api url to determine the
+    canonical repository url.
+
+    """
+    url_ = url.lower()
+
+    match = GITHUB_PATTERN.match(url_)
+    if not match:
+        return url
+
+    user_repo = _sanitize_github_url(match.groupdict()["user_repo"])
+    response = requests.get(_url_github_api(user_repo))
+    if response.status_code != 200:
+        return None
+    data = response.json()
+    return data["html_url"]

swh/core/tests/test_github_utils.py

+# Copyright (C) 2022  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+import pytest
+
+from swh.core.github.utils import (
+    _sanitize_github_url,
+    _url_github_api,
+    _url_github_html,
+    get_canonical_github_origin_url,
+)
+
+KNOWN_GH_REPO = "https://github.com/user/repo"
+
+
+@pytest.mark.parametrize(
+    "user_repo, expected_url",
+    [
+        ("user/repo.git", KNOWN_GH_REPO),
+        ("user/repo.git/", KNOWN_GH_REPO),
+        ("user/repo/", KNOWN_GH_REPO),
+        ("user/repo", KNOWN_GH_REPO),
+        ("user/repo/.git", KNOWN_GH_REPO),
+        # edge cases
+        ("https://github.com/unknown-page", None),  # unknown gh origin returns None
+        ("user/repo/with/some/deps", None),  # url kind is not dealt with for now
+    ],
+)
+def test_get_canonical_github_origin_url(user_repo, expected_url, requests_mock):
+    """It should return a canonical github origin when it exists, None otherwise"""
+    html_url = _url_github_html(user_repo)
+    api_url = _url_github_api(_sanitize_github_url(user_repo))
+
+    if expected_url is not None:
+        status_code = 200
+        response = {"html_url": _sanitize_github_url(html_url)}
+    else:
+        status_code = 404
+        response = {}
+
+    requests_mock.get(api_url, [{"status_code": status_code, "json": response}])
+
+    assert get_canonical_github_origin_url(html_url) == expected_url
+
+
+def test_get_canonical_github_origin_url_not_gh_origin():
+    """It should return the input url when that origin is not a github one"""
+    url = "https://example.org"
+    assert get_canonical_github_origin_url(url) == url