Check the URL scheme before downloading in generate_docset.py (#5803)

Codacy flagged two Bandit findings in the docset generator added in
#5799: B310 (urlopen with an unchecked scheme) and B506 (yaml.load).
download() now rejects anything but http(s) URLs before opening them,
and the yaml.load call is marked, since its Loader derives from
yaml.SafeLoader. The SHA-1 used to name downloaded files is marked as
not used for security.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/docset/generate_docset.py

@@ -337,14 +337,17 @@ def is_remote(url) -> bool:
 def download(url, docs) -> str:
     """Download url into assets/external and return the path relative to docs."""
     u = urllib.parse.urlparse(url if not url.startswith('//') else 'https:' + url)
+    if u.scheme.lower() not in ('http', 'https'):
+        raise ValueError(f'not an http(s) URL: {url}')
     req = urllib.request.Request(u.geturl(), headers={'User-Agent': USER_AGENT})
-    with urllib.request.urlopen(req, timeout=20) as r:
+    # (the scheme is checked above)
+    with urllib.request.urlopen(req, timeout=20) as r:  # nosec B310
         data = r.read()
         ctype = r.headers.get_content_type()
     path = urllib.parse.unquote(u.path).lstrip('/')
     ext = os.path.splitext(path)[1]
     if u.query or not ext or path.endswith('/'):
-        digest = hashlib.sha1(url.encode()).hexdigest()[:12]
+        digest = hashlib.sha1(url.encode(), usedforsecurity=False).hexdigest()[:12]
         path = os.path.join(os.path.dirname(path), digest + CONTENT_TYPE_EXT.get(ctype, ext or '.bin'))
     rel = os.path.normpath(os.path.join('assets', 'external', u.hostname, path))
     out = os.path.join(docs, rel)
@@ -385,7 +388,8 @@ def localize_images(docs) -> None:
 def load_mkdocs_yml() -> dict:
     """Load mkdocs.yml, ignoring tags like !ENV and !!python/name."""
     with open(MKDOCS_YML, encoding='utf-8') as f:
-        return yaml.load(f, Loader=Loader)
+        # (Loader is a yaml.SafeLoader)
+        return yaml.load(f, Loader=Loader)  # nosec B506
 
 
 def localize_site_urls(docs, site_url) -> None: