Merge branch 'release-v1.14.0' of github.com:matrix-org/synapse into dinsic-release-v1.14.x

* 'release-v1.14.0' of github.com:matrix-org/synapse: (108 commits)
  Fix typo in PR link
  Update debian changelog
  1.14.0
  Improve changelog wording
  1.14.0rc2
  Fix sample config docs error (#7581)
  Fix up comments
  Fix specifying cache factors via env vars with * in name. (#7580)
  Don't apply cache factor to event cache. (#7578)
  Ensure ReplicationStreamer is always started when replication enabled. (#7579)
  Remove the changes to the debian changelog
  Not full release yet, this is rc1
  Merge event persistence move changelog entries
  More changelog fix
  Changelog fixes
  1.14.0
  Replace device_27_unique_idx bg update with a fg one (#7562)
  Fix incorrect exception handling in KeyUploadServlet.on_POST (#7563)
  Fix recording of federation stream token (#7564)
  Simplify reap_monthly_active_users (#7558)
  ...

10 files changed, 225 insertions, 175 deletions

diff --git a/synapse/util/caches/__init__.py b/synapse/util/caches/__init__.py
index da5077b471..dd356bf156 100644
--- a/synapse/util/caches/__init__.py
+++ b/synapse/util/caches/__init__.py
@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 # Copyright 2015, 2016 OpenMarket Ltd
-# Copyright 2019 The Matrix.org Foundation C.I.C.
+# Copyright 2019, 2020 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -15,28 +15,16 @@
 # limitations under the License.
 
 import logging
-import os
-from typing import Dict
+from sys import intern
+from typing import Callable, Dict, Optional
 
-import six
-from six.moves import intern
+import attr
+from prometheus_client.core import Gauge
 
-from prometheus_client.core import REGISTRY, Gauge, GaugeMetricFamily
+from synapse.config.cache import add_resizable_cache
 
 logger = logging.getLogger(__name__)
 
-CACHE_SIZE_FACTOR = float(os.environ.get("SYNAPSE_CACHE_FACTOR", 0.5))
-
-
-def get_cache_factor_for(cache_name):
-    env_var = "SYNAPSE_CACHE_FACTOR_" + cache_name.upper()
-    factor = os.environ.get(env_var)
-    if factor:
-        return float(factor)
-
-    return CACHE_SIZE_FACTOR
-
-
 caches_by_name = {}
 collectors_by_name = {}  # type: Dict
 
@@ -44,6 +32,7 @@ cache_size = Gauge("synapse_util_caches_cache:size", "", ["name"])
 cache_hits = Gauge("synapse_util_caches_cache:hits", "", ["name"])
 cache_evicted = Gauge("synapse_util_caches_cache:evicted_size", "", ["name"])
 cache_total = Gauge("synapse_util_caches_cache:total", "", ["name"])
+cache_max_size = Gauge("synapse_util_caches_cache_max_size", "", ["name"])
 
 response_cache_size = Gauge("synapse_util_caches_response_cache:size", "", ["name"])
 response_cache_hits = Gauge("synapse_util_caches_response_cache:hits", "", ["name"])
@@ -53,67 +42,82 @@ response_cache_evicted = Gauge(
 response_cache_total = Gauge("synapse_util_caches_response_cache:total", "", ["name"])
 
 
-def register_cache(cache_type, cache_name, cache, collect_callback=None):
-    """Register a cache object for metric collection.
+@attr.s
+class CacheMetric(object):
+
+    _cache = attr.ib()
+    _cache_type = attr.ib(type=str)
+    _cache_name = attr.ib(type=str)
+    _collect_callback = attr.ib(type=Optional[Callable])
+
+    hits = attr.ib(default=0)
+    misses = attr.ib(default=0)
+    evicted_size = attr.ib(default=0)
+
+    def inc_hits(self):
+        self.hits += 1
+
+    def inc_misses(self):
+        self.misses += 1
+
+    def inc_evictions(self, size=1):
+        self.evicted_size += size
+
+    def describe(self):
+        return []
+
+    def collect(self):
+        try:
+            if self._cache_type == "response_cache":
+                response_cache_size.labels(self._cache_name).set(len(self._cache))
+                response_cache_hits.labels(self._cache_name).set(self.hits)
+                response_cache_evicted.labels(self._cache_name).set(self.evicted_size)
+                response_cache_total.labels(self._cache_name).set(
+                    self.hits + self.misses
+                )
+            else:
+                cache_size.labels(self._cache_name).set(len(self._cache))
+                cache_hits.labels(self._cache_name).set(self.hits)
+                cache_evicted.labels(self._cache_name).set(self.evicted_size)
+                cache_total.labels(self._cache_name).set(self.hits + self.misses)
+                if getattr(self._cache, "max_size", None):
+                    cache_max_size.labels(self._cache_name).set(self._cache.max_size)
+            if self._collect_callback:
+                self._collect_callback()
+        except Exception as e:
+            logger.warning("Error calculating metrics for %s: %s", self._cache_name, e)
+            raise
+
+
+def register_cache(
+    cache_type: str,
+    cache_name: str,
+    cache,
+    collect_callback: Optional[Callable] = None,
+    resizable: bool = True,
+    resize_callback: Optional[Callable] = None,
+) -> CacheMetric:
+    """Register a cache object for metric collection and resizing.
 
     Args:
-        cache_type (str):
-        cache_name (str): name of the cache
-        cache (object): cache itself
-        collect_callback (callable|None): if not None, a function which is called during
-            metric collection to update additional metrics.
+        cache_type
+        cache_name: name of the cache
+        cache: cache itself
+        collect_callback: If given, a function which is called during metric
+            collection to update additional metrics.
+        resizable: Whether this cache supports being resized.
+        resize_callback: A function which can be called to resize the cache.
 
     Returns:
         CacheMetric: an object which provides inc_{hits,misses,evictions} methods
     """
+    if resizable:
+        if not resize_callback:
+            resize_callback = getattr(cache, "set_cache_factor")
+        add_resizable_cache(cache_name, resize_callback)
 
-    # Check if the metric is already registered. Unregister it, if so.
-    # This usually happens during tests, as at runtime these caches are
-    # effectively singletons.
+    metric = CacheMetric(cache, cache_type, cache_name, collect_callback)
     metric_name = "cache_%s_%s" % (cache_type, cache_name)
-    if metric_name in collectors_by_name.keys():
-        REGISTRY.unregister(collectors_by_name[metric_name])
-
-    class CacheMetric(object):
-
-        hits = 0
-        misses = 0
-        evicted_size = 0
-
-        def inc_hits(self):
-            self.hits += 1
-
-        def inc_misses(self):
-            self.misses += 1
-
-        def inc_evictions(self, size=1):
-            self.evicted_size += size
-
-        def describe(self):
-            return []
-
-        def collect(self):
-            try:
-                if cache_type == "response_cache":
-                    response_cache_size.labels(cache_name).set(len(cache))
-                    response_cache_hits.labels(cache_name).set(self.hits)
-                    response_cache_evicted.labels(cache_name).set(self.evicted_size)
-                    response_cache_total.labels(cache_name).set(self.hits + self.misses)
-                else:
-                    cache_size.labels(cache_name).set(len(cache))
-                    cache_hits.labels(cache_name).set(self.hits)
-                    cache_evicted.labels(cache_name).set(self.evicted_size)
-                    cache_total.labels(cache_name).set(self.hits + self.misses)
-                if collect_callback:
-                    collect_callback()
-            except Exception as e:
-                logger.warning("Error calculating metrics for %s: %s", cache_name, e)
-                raise
-
-            yield GaugeMetricFamily("__unused", "")
-
-    metric = CacheMetric()
-    REGISTRY.register(metric)
     caches_by_name[cache_name] = cache
     collectors_by_name[metric_name] = metric
     return metric
@@ -148,9 +152,6 @@ def intern_string(string):
         return None
 
     try:
-        if six.PY2:
-            string = string.encode("ascii")
-
         return intern(string)
     except UnicodeEncodeError:
         return string
diff --git a/synapse/util/caches/descriptors.py b/synapse/util/caches/descriptors.py
index 2e8f6543e5..cd48262420 100644
--- a/synapse/util/caches/descriptors.py
+++ b/synapse/util/caches/descriptors.py
@@ -13,6 +13,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+
 import functools
 import inspect
 import logging
@@ -30,7 +31,6 @@ from twisted.internet import defer
 from synapse.logging.context import make_deferred_yieldable, preserve_fn
 from synapse.util import unwrapFirstError
 from synapse.util.async_helpers import ObservableDeferred
-from synapse.util.caches import get_cache_factor_for
 from synapse.util.caches.lrucache import LruCache
 from synapse.util.caches.treecache import TreeCache, iterate_tree_cache_entry
 
@@ -81,7 +81,6 @@ class CacheEntry(object):
 class Cache(object):
     __slots__ = (
         "cache",
-        "max_entries",
         "name",
         "keylen",
         "thread",
@@ -89,7 +88,29 @@ class Cache(object):
         "_pending_deferred_cache",
     )
 
-    def __init__(self, name, max_entries=1000, keylen=1, tree=False, iterable=False):
+    def __init__(
+        self,
+        name: str,
+        max_entries: int = 1000,
+        keylen: int = 1,
+        tree: bool = False,
+        iterable: bool = False,
+        apply_cache_factor_from_config: bool = True,
+    ):
+        """
+        Args:
+            name: The name of the cache
+            max_entries: Maximum amount of entries that the cache will hold
+            keylen: The length of the tuple used as the cache key
+            tree: Use a TreeCache instead of a dict as the underlying cache type
+            iterable: If True, count each item in the cached object as an entry,
+                rather than each cached object
+            apply_cache_factor_from_config: Whether cache factors specified in the
+                config file affect `max_entries`
+
+        Returns:
+            Cache
+        """
         cache_type = TreeCache if tree else dict
         self._pending_deferred_cache = cache_type()
 
@@ -99,6 +120,7 @@ class Cache(object):
             cache_type=cache_type,
             size_callback=(lambda d: len(d)) if iterable else None,
             evicted_callback=self._on_evicted,
+            apply_cache_factor_from_config=apply_cache_factor_from_config,
         )
 
         self.name = name
@@ -111,6 +133,10 @@ class Cache(object):
             collect_callback=self._metrics_collection_callback,
         )
 
+    @property
+    def max_entries(self):
+        return self.cache.max_size
+
     def _on_evicted(self, evicted_count):
         self.metrics.inc_evictions(evicted_count)
 
@@ -370,13 +396,11 @@ class CacheDescriptor(_CacheDescriptorBase):
             cache_context=cache_context,
         )
 
-        max_entries = int(max_entries * get_cache_factor_for(orig.__name__))
-
         self.max_entries = max_entries
         self.tree = tree
         self.iterable = iterable
 
-    def __get__(self, obj, objtype=None):
+    def __get__(self, obj, owner):
         cache = Cache(
             name=self.orig.__name__,
             max_entries=self.max_entries,
diff --git a/synapse/util/caches/expiringcache.py b/synapse/util/caches/expiringcache.py
index cddf1ed515..2726b67b6d 100644
--- a/synapse/util/caches/expiringcache.py
+++ b/synapse/util/caches/expiringcache.py
@@ -18,6 +18,7 @@ from collections import OrderedDict
 
 from six import iteritems, itervalues
 
+from synapse.config import cache as cache_config
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.util.caches import register_cache
 
@@ -51,15 +52,16 @@ class ExpiringCache(object):
                 an item on access. Defaults to False.
             iterable (bool): If true, the size is calculated by summing the
                 sizes of all entries, rather than the number of entries.
-
         """
         self._cache_name = cache_name
 
+        self._original_max_size = max_len
+
+        self._max_size = int(max_len * cache_config.properties.default_factor_size)
+
         self._clock = clock
 
-        self._max_len = max_len
         self._expiry_ms = expiry_ms
-
         self._reset_expiry_on_get = reset_expiry_on_get
 
         self._cache = OrderedDict()
@@ -82,9 +84,11 @@ class ExpiringCache(object):
     def __setitem__(self, key, value):
         now = self._clock.time_msec()
         self._cache[key] = _CacheEntry(now, value)
+        self.evict()
 
+    def evict(self):
         # Evict if there are now too many items
-        while self._max_len and len(self) > self._max_len:
+        while self._max_size and len(self) > self._max_size:
             _key, value = self._cache.popitem(last=False)
             if self.iterable:
                 self.metrics.inc_evictions(len(value.value))
@@ -170,6 +174,23 @@ class ExpiringCache(object):
         else:
             return len(self._cache)
 
+    def set_cache_factor(self, factor: float) -> bool:
+        """
+        Set the cache factor for this individual cache.
+
+        This will trigger a resize if it changes, which may require evicting
+        items from the cache.
+
+        Returns:
+            bool: Whether the cache changed size or not.
+        """
+        new_size = int(self._original_max_size * factor)
+        if new_size != self._max_size:
+            self._max_size = new_size
+            self.evict()
+            return True
+        return False
+
 
 class _CacheEntry(object):
     __slots__ = ["time", "value"]
diff --git a/synapse/util/caches/lrucache.py b/synapse/util/caches/lrucache.py
index 1536cb64f3..df4ea5901d 100644
--- a/synapse/util/caches/lrucache.py
+++ b/synapse/util/caches/lrucache.py
@@ -13,10 +13,11 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-
 import threading
 from functools import wraps
+from typing import Callable, Optional, Type, Union
 
+from synapse.config import cache as cache_config
 from synapse.util.caches.treecache import TreeCache
 
 
@@ -52,17 +53,18 @@ class LruCache(object):
 
     def __init__(
         self,
-        max_size,
-        keylen=1,
-        cache_type=dict,
-        size_callback=None,
-        evicted_callback=None,
+        max_size: int,
+        keylen: int = 1,
+        cache_type: Type[Union[dict, TreeCache]] = dict,
+        size_callback: Optional[Callable] = None,
+        evicted_callback: Optional[Callable] = None,
+        apply_cache_factor_from_config: bool = True,
     ):
         """
         Args:
-            max_size (int):
+            max_size: The maximum amount of entries the cache can hold
 
-            keylen (int):
+            keylen: The length of the tuple used as the cache key
 
             cache_type (type):
                 type of underlying cache to be used. Typically one of dict
@@ -73,9 +75,24 @@ class LruCache(object):
             evicted_callback (func(int)|None):
                 if not None, called on eviction with the size of the evicted
                 entry
+
+            apply_cache_factor_from_config (bool): If true, `max_size` will be
+                multiplied by a cache factor derived from the homeserver config
         """
         cache = cache_type()
         self.cache = cache  # Used for introspection.
+        self.apply_cache_factor_from_config = apply_cache_factor_from_config
+
+        # Save the original max size, and apply the default size factor.
+        self._original_max_size = max_size
+        # We previously didn't apply the cache factor here, and as such some caches were
+        # not affected by the global cache factor. Add an option here to disable applying
+        # the cache factor when a cache is created
+        if apply_cache_factor_from_config:
+            self.max_size = int(max_size * cache_config.properties.default_factor_size)
+        else:
+            self.max_size = int(max_size)
+
         list_root = _Node(None, None, None, None)
         list_root.next_node = list_root
         list_root.prev_node = list_root
@@ -83,7 +100,7 @@ class LruCache(object):
         lock = threading.Lock()
 
         def evict():
-            while cache_len() > max_size:
+            while cache_len() > self.max_size:
                 todelete = list_root.prev_node
                 evicted_len = delete_node(todelete)
                 cache.pop(todelete.key, None)
@@ -236,6 +253,7 @@ class LruCache(object):
             return key in cache
 
         self.sentinel = object()
+        self._on_resize = evict
         self.get = cache_get
         self.set = cache_set
         self.setdefault = cache_set_default
@@ -266,3 +284,23 @@ class LruCache(object):
 
     def __contains__(self, key):
         return self.contains(key)
+
+    def set_cache_factor(self, factor: float) -> bool:
+        """
+        Set the cache factor for this individual cache.
+
+        This will trigger a resize if it changes, which may require evicting
+        items from the cache.
+
+        Returns:
+            bool: Whether the cache changed size or not.
+        """
+        if not self.apply_cache_factor_from_config:
+            return False
+
+        new_size = int(self._original_max_size * factor)
+        if new_size != self.max_size:
+            self.max_size = new_size
+            self._on_resize()
+            return True
+        return False
diff --git a/synapse/util/caches/response_cache.py b/synapse/util/caches/response_cache.py
index b68f9fe0d4..a6c60888e5 100644
--- a/synapse/util/caches/response_cache.py
+++ b/synapse/util/caches/response_cache.py
@@ -38,7 +38,7 @@ class ResponseCache(object):
         self.timeout_sec = timeout_ms / 1000.0
 
         self._name = name
-        self._metrics = register_cache("response_cache", name, self)
+        self._metrics = register_cache("response_cache", name, self, resizable=False)
 
     def size(self):
         return len(self.pending_result_cache)
diff --git a/synapse/util/caches/stream_change_cache.py b/synapse/util/caches/stream_change_cache.py
index e54f80d76e..2a161bf244 100644
--- a/synapse/util/caches/stream_change_cache.py
+++ b/synapse/util/caches/stream_change_cache.py
@@ -14,6 +14,7 @@
 # limitations under the License.
 
 import logging
+import math
 from typing import Dict, FrozenSet, List, Mapping, Optional, Set, Union
 
 from six import integer_types
@@ -46,7 +47,8 @@ class StreamChangeCache:
         max_size=10000,
         prefilled_cache: Optional[Mapping[EntityType, int]] = None,
     ):
-        self._max_size = int(max_size * caches.CACHE_SIZE_FACTOR)
+        self._original_max_size = max_size
+        self._max_size = math.floor(max_size)
         self._entity_to_key = {}  # type: Dict[EntityType, int]
 
         # map from stream id to the a set of entities which changed at that stream id.
@@ -58,12 +60,31 @@ class StreamChangeCache:
         #
         self._earliest_known_stream_pos = current_stream_pos
         self.name = name
-        self.metrics = caches.register_cache("cache", self.name, self._cache)
+        self.metrics = caches.register_cache(
+            "cache", self.name, self._cache, resize_callback=self.set_cache_factor
+        )
 
         if prefilled_cache:
             for entity, stream_pos in prefilled_cache.items():
                 self.entity_has_changed(entity, stream_pos)
 
+    def set_cache_factor(self, factor: float) -> bool:
+        """
+        Set the cache factor for this individual cache.
+
+        This will trigger a resize if it changes, which may require evicting
+        items from the cache.
+
+        Returns:
+            bool: Whether the cache changed size or not.
+        """
+        new_size = math.floor(self._original_max_size * factor)
+        if new_size != self._max_size:
+            self.max_size = new_size
+            self._evict()
+            return True
+        return False
+
     def has_entity_changed(self, entity: EntityType, stream_pos: int) -> bool:
         """Returns True if the entity may have been updated since stream_pos
         """
@@ -171,6 +192,7 @@ class StreamChangeCache:
             e1 = self._cache[stream_pos] = set()
         e1.add(entity)
         self._entity_to_key[entity] = stream_pos
+        self._evict()
 
         # if the cache is too big, remove entries
         while len(self._cache) > self._max_size:
@@ -179,6 +201,13 @@ class StreamChangeCache:
             for entity in r:
                 del self._entity_to_key[entity]
 
+    def _evict(self):
+        while len(self._cache) > self._max_size:
+            k, r = self._cache.popitem(0)
+            self._earliest_known_stream_pos = max(k, self._earliest_known_stream_pos)
+            for entity in r:
+                self._entity_to_key.pop(entity, None)
+
     def get_max_pos_of_last_change(self, entity: EntityType) -> int:
 
         """Returns an upper bound of the stream id of the last change to an
diff --git a/synapse/util/caches/ttlcache.py b/synapse/util/caches/ttlcache.py
index 99646c7cf0..6437aa907e 100644
--- a/synapse/util/caches/ttlcache.py
+++ b/synapse/util/caches/ttlcache.py
@@ -38,7 +38,7 @@ class TTLCache(object):
 
         self._timer = timer
 
-        self._metrics = register_cache("ttl", cache_name, self)
+        self._metrics = register_cache("ttl", cache_name, self, resizable=False)
 
     def set(self, key, value, ttl):
         """Add/update an entry in the cache
diff --git a/synapse/util/frozenutils.py b/synapse/util/frozenutils.py
index f2ccd5e7c6..9815bb8667 100644
--- a/synapse/util/frozenutils.py
+++ b/synapse/util/frozenutils.py
@@ -65,5 +65,5 @@ def _handle_frozendict(obj):
     )
 
 
-# A JSONEncoder which is capable of encoding frozendics without barfing
+# A JSONEncoder which is capable of encoding frozendicts without barfing
 frozendict_json_encoder = json.JSONEncoder(default=_handle_frozendict)
diff --git a/synapse/util/patch_inline_callbacks.py b/synapse/util/patch_inline_callbacks.py
index fdff195771..2605f3c65b 100644
--- a/synapse/util/patch_inline_callbacks.py
+++ b/synapse/util/patch_inline_callbacks.py
@@ -186,10 +186,15 @@ def _check_yield_points(f: Callable, changes: List[str]):
                     )
                     raise Exception(err)
 
+            # the wrapped function yielded a Deferred: yield it back up to the parent
+            # inlineCallbacks().
             try:
                 result = yield d
-            except Exception as e:
-                result = Failure(e)
+            except Exception:
+                # this will fish an earlier Failure out of the stack where possible, and
+                # thus is preferable to passing in an exeception to the Failure
+                # constructor, since it results in less stack-mangling.
+                result = Failure()
 
             if current_context() != expected_context:
 
diff --git a/synapse/util/stringutils.py b/synapse/util/stringutils.py
index 6899bcb788..08c86e92b8 100644
--- a/synapse/util/stringutils.py
+++ b/synapse/util/stringutils.py
@@ -19,10 +19,6 @@ import re
 import string
 from collections import Iterable
 
-import six
-from six import PY2, PY3
-from six.moves import range
-
 from synapse.api.errors import Codes, SynapseError
 
 _string_with_symbols = string.digits + string.ascii_letters + ".,;:^&*-_+=#~@"
@@ -47,80 +43,16 @@ def random_string_with_symbols(length):
 
 
 def is_ascii(s):
-
-    if PY3:
-        if isinstance(s, bytes):
-            try:
-                s.decode("ascii").encode("ascii")
-            except UnicodeDecodeError:
-                return False
-            except UnicodeEncodeError:
-                return False
-            return True
-
-    try:
-        s.encode("ascii")
-    except UnicodeEncodeError:
-        return False
-    except UnicodeDecodeError:
-        return False
-    else:
+    if isinstance(s, bytes):
+        try:
+            s.decode("ascii").encode("ascii")
+        except UnicodeDecodeError:
+            return False
+        except UnicodeEncodeError:
+            return False
         return True
 
 
-def to_ascii(s):
-    """Converts a string to ascii if it is ascii, otherwise leave it alone.
-
-    If given None then will return None.
-    """
-    if PY3:
-        return s
-
-    if s is None:
-        return None
-
-    try:
-        return s.encode("ascii")
-    except UnicodeEncodeError:
-        return s
-
-
-def exception_to_unicode(e):
-    """Helper function to extract the text of an exception as a unicode string
-
-    Args:
-        e (Exception): exception to be stringified
-
-    Returns:
-        unicode
-    """
-    # urgh, this is a mess. The basic problem here is that psycopg2 constructs its
-    # exceptions with PyErr_SetString, with a (possibly non-ascii) argument. str() will
-    # then produce the raw byte sequence. Under Python 2, this will then cause another
-    # error if it gets mixed with a `unicode` object, as per
-    # https://github.com/matrix-org/synapse/issues/4252
-
-    # First of all, if we're under python3, everything is fine because it will sort this
-    # nonsense out for us.
-    if not PY2:
-        return str(e)
-
-    # otherwise let's have a stab at decoding the exception message. We'll circumvent
-    # Exception.__str__(), which would explode if someone raised Exception(u'non-ascii')
-    # and instead look at what is in the args member.
-
-    if len(e.args) == 0:
-        return ""
-    elif len(e.args) > 1:
-        return six.text_type(repr(e.args))
-
-    msg = e.args[0]
-    if isinstance(msg, bytes):
-        return msg.decode("utf-8", errors="replace")
-    else:
-        return msg
-
-
 def assert_valid_client_secret(client_secret):
     """Validate that a given string matches the client_secret regex defined by the spec"""
     if client_secret_regex.match(client_secret) is None: