Workarounds for servers not supporting multiplexing auth

Fixes #564

Author: tobixen

AI_POLICY.md

@@ -12,7 +12,7 @@ started receiving pull requests with code changes generated by AI (and
 I've seen people posting screenshots of simple questions and answers
 from ChatGPT in forum discussions, without contributing anything else).
 
-As of 2025-11, I've spent some time testing Claude.  I'm actually
+As of 2025-12, I've spent some time testing Claude.  I'm actually
 positively surprised, it's doing a much better job than what I had
 expected.  The AI may do things faster, smarter and better than a good
 coder.  Sometimes.  Other times it may spend a lot of "tokens" and a
@@ -59,12 +59,12 @@ experiences is that the AI performs best when being "supervised" and
   should be informed about both in the pull request itself and in the
   git commit message.  The most common way to do this is to add
   "Assisted-by: (name of AI-tool)" at the end of the message.  Claude
-  seems to sign off with "Co-Authored-By: Claude
-  <noreply@anthropic.com>" when it's doing commits, that's also OK.
+  seems to sign off with `Co-Authored-By: Claude
+  <noreply@anthropic.com>` when it's doing commits, that's also OK.
 
 * **YOU** should be ready to follow up and respond to feedback and
   questions on the contribution.  If all you do is to relay it to the
-  AI and relaying the AI thoughts back to the pull request, then
+  AI and relaying the AI output back to the pull request, then
   you're not adding value to the project and you're not transparent
   and honest.  You should at least do a quick QA on the AI-answer and
   acknowledge that it was generated by the AI.

caldav/compatibility_hints.py

@@ -92,6 +92,10 @@ class FeatureSet:
         "delete-calendar.free-namespace": {
             "description": "The delete operations clears the namespace, so that another calendar with the same ID/name can be created"
         },
+        "http": { },
+        "http.multiplexing": {
+            "description": "chulka/baikal:nginx is having Problems with using HTTP/2 with multiplexing, ref https://github.com/python-caldav/caldav/issues/564.  I haven't (yet) been able to reproduce this locally, so no check for this yet.  We'll define it as fragile in the radicale config as for now"
+        },
         "save-load": {
             "description": "it's possible to save and load objects to the calendar"
         },
@@ -264,6 +268,26 @@ def __init__(self, feature_set_dict=None):
         if feature_set_dict:
             self.copyFeatureSet(feature_set_dict, collapse=False)
 
+
+    def set_feature(self, feature, value=True):
+        if isinstance(value, dict):
+            fc = {feature: value}
+        elif isinstance(value, str):
+            fc = {feature: {"support": value}}
+        elif value is True:
+            fc = {feature: {"support": "full"}}
+        elif value is False:
+            fc = {feature: {"support": "unsupported"}}
+        elif value is None:
+            fc = {feature: {"support": "unknown"}}
+        else:
+            assert False
+        self.copyFeatureSet(fc, collapse=False)
+        feat_def = self.find_feature(feature)
+        feat_type = feat_def.get('type', 'server-feature')
+        sup = fc[feature].get('support', feat_def.get('default', 'full'))
+
+
     ## TODO: Why is this camelCase while every other method is with under_score?  rename ...
     def copyFeatureSet(self, feature_set, collapse=True):
         for feature in feature_set:
@@ -880,6 +904,7 @@ def dotted_feature_set_list(self, compact=False):
 }
 
 baikal =  { ## version 0.10.1
+    "http.multiplexing": "fragile", ## ref https://github.com/python-caldav/caldav/issues/564
     "save-load.journal": {'support': 'ungraceful'},
     #'search.comp-type-optional': {'support': 'ungraceful'}, ## Possibly this has been fixed?
     'search.recurrences.expanded.todo': {'support': 'unsupported'},

caldav/davclient.py

@@ -599,18 +599,19 @@ def __init__(
         """
         headers = headers or {}
 
-        ## Deprecation TODO: give a warning, user should use get_davclient or auto_calendar instead
-
-        try:
-            self.session = requests.Session(multiplexed=True)
-        except TypeError:
-            self.session = requests.Session()
+        ## Deprecation TODO: give a warning, user should use get_davclient or auto_calendar instead.  Probably.
 
         if isinstance(features, str):
             features = getattr(caldav.compatibility_hints, features)
         self.features = FeatureSet(features)
         self.huge_tree = huge_tree
 
+        try:
+            multiplexed = self.features.is_supported("http.multiplexing")
+            self.session = requests.Session(multiplexed=multiplexed)
+        except TypeError:
+            self.session = requests.Session()
+
         url, discovered_username = _auto_url(
             url,
             self.features,
@@ -1100,6 +1101,24 @@ def request(
             and self.password
             and isinstance(self.password, bytes)
         ):
+            ## TODO: this has become a mess and should be refactored.
+            ## (Arguably, this logic doesn't belong here at all.
+            ## with niquests it's possible to just pass the username
+            ## and password, maybe we should try that?)
+
+            ## Most likely we're here due to wrong username/password
+            ## combo, but it could also be a multiplexing problem.
+            if (
+                self.features.is_supported("http.multiplexing", return_defaults=False)
+                is None
+            ):
+                self.session = requests.Session()
+                self.features.set_feature("http.multiplexing", "unknown")
+                ## If this one also fails, we give up
+                ret = self.request(str(url_obj), method, body, headers)
+                self.features.set_feature("http.multiplexing", False)
+                return ret
+
             ## Most likely we're here due to wrong username/password
             ## combo, but it could also be charset problems.  Some
             ## (ancient) servers don't like UTF-8 binary auth with
@@ -1115,6 +1134,7 @@ def request(
 
             self.username = None
             self.password = None
+
             return self.request(str(url_obj), method, body, headers)
 
         if error.debug_dump_communication: