Tweak the rules for to_canonical to better handle subdirs.

realms/lib/util.py

@@ -83,24 +83,25 @@ def clean_url(url):
 
 def to_canonical(s):
     """
-    Remove leading/trailing whitespace
-    Remove leading underscores and backslashes "/"
+    Remove leading/trailing whitespace (from all path components)
+    Remove leading underscores and slashes "/"
     Convert spaces to dashes "-"
-    Limit to first 128 chars
+    Limit path components to 63 chars and total size to 436 chars
     """
     reserved_chars = "&$+,:;=?@#"
     unsafe_chars = "?<>[]{}|\^~%"
 
-    s = s.encode('utf8')
-    s = str(s)
-    s = s.strip()
-    s = s.lstrip('_')
-    s = s.lstrip('/')
-    s = re.sub(r"\s", "-", s)
-    s = re.sub(r"/+", "/", s)
+    s = s.encode("utf8")
+    s = re.sub(r"\s+", " ", s)
+    s = s.lstrip("_/ ")
     s = re.sub(r"[" + re.escape(reserved_chars) + "]", "", s)
     s = re.sub(r"[" + re.escape(unsafe_chars) + "]", "", s)
-    s = s[:128]
+    # Strip leading/trailing spaces from path components, replace internal spaces
+    # with '-', and truncate to 63 characters.
+    parts = (part.strip().replace(" ", "-")[:63] for part in s.split("/"))
+    # Join any non-empty path components back together
+    s = "/".join(filter(None, parts))
+    s = s[:436]
     return s