lib/mntpt: Add explicit filtering depending on scheme

In the old source code we already filtered NEO URI by dropping
credentials, but we applied this filter to any URI, not only the NEO
one. This patch adds a mechanism to apply various filter according to
the specific storage type. Starting with this new patch, 'zstor_2mntpt'
also refuses to calculate the mountpoint for URI with unknown scheme.

lib/mntpt.py

@@ -29,14 +29,21 @@ from six.moves.urllib.parse import urlsplit, urlunsplit
 #
 # it also makes sure the mountpoint exists.
 def mntpt_4zurl(zurl):
-    # remove credentials from zurl.
-    # The same database can be accessed from different clients with different
-    # credentials, but we want to map them all to the same single WCFS
-    # instance.
+    # Filter URI in order to make mntpt persistent among different clients with
+    # varying client options: the WCFS URI should always keep the same if the
+    # same storage is meant.
     scheme, netloc, path, query, frag = urlsplit(zurl)
-    if "@" in netloc:
-        netloc = netloc[netloc.index("@") + 1 :]
-    zurl = urlunsplit((scheme, netloc, path, query, frag))
+
+    try:
+        # The filtering depends on the storage backend (there is no standard
+        # among ZODB storages).
+        f = globals()["_filter_%s" % scheme.lower()]
+    except KeyError:
+        raise NotImplementedError(
+            "can't calculate mountpoint for storage with scheme %s" % scheme
+        )
+
+    zurl = urlunsplit(f(scheme, netloc, path, query, frag))
 
     m = hashlib.sha1()
     m.update(zurl)
@@ -63,6 +70,27 @@ def mntpt_4zurl(zurl):
     return mntpt
 
 
+# Supported storages, but no filtering applied yet.
+_filter = lambda *args: args
+_filter_demo = _filter
+_filter_file = _filter
+_filter_zeo = _filter
+
+
+def _filter_neo(scheme, netloc, path, query, frag):
+    # remove credentials from zurl.
+    # The same database can be accessed from different clients with different
+    # credentials, but we want to map them all to the same single WCFS
+    # instance.
+    if "@" in netloc:
+        netloc = netloc[netloc.index("@") + 1 :]
+    return (scheme, netloc, path, query, frag)
+
+
+# Alias for neo scheme with SSL encryption
+_filter_neos = _filter_neo
+
+
 # mkdir -p.
 def _mkdir_p(path, mode=0o777): # -> created(bool)
     try: