fix(flask-caching): support v2.0 (DataDog#3882)

## Description

flask-caching released version 2.0 which moves the cache client to a new library
called [`cachelib`](https://github.com/pallets-eco/cachelib).

Diff here: pallets-eco/flask-caching@v1.10.0...v2.0.0

This breaks our logic which collects tags for the redis client.

## Fix

It was noticed that both `_write_client` and `_read_client` use the same connection information
so we don't need to dynamically check for each.

Also [`_read_clients`](https://github.com/pallets-eco/flask-caching/blob/ac13e01baa11d65c68dcba64f99ccaafd9b5419c/src/flask_caching/backends/rediscache.py#L62) was moved to [`_read_client`](https://github.com/pallets-eco/cachelib/blob/13c8bf8db156dd06154f5e08e23bdd9e73480a5b/src/cachelib/redis.py#L29) when the logic was moved to `cachelib`.

ddtrace/contrib/flask_cache/tracers.py

@@ -3,6 +3,7 @@
 """
 
 import logging
+import typing
 
 from ddtrace import config
 
@@ -14,6 +15,10 @@
 from .utils import _resource_from_cache_prefix
 
 
+if typing.TYPE_CHECKING:
+    from ddtrace import Span
+
+
 log = logging.Logger(__name__)
 
 DEFAULT_SERVICE = config.service or "flask-cache"
@@ -55,7 +60,8 @@ class TracedCache(cache_cls):
         _datadog_service = service
         _datadog_meta = meta
 
-        def __trace(self, cmd, write=False):
+        def __trace(self, cmd):
+            # type: (str, bool) -> Span
             """
             Start a tracing with default attributes and tags
             """
@@ -68,7 +74,7 @@ def __trace(self, cmd, write=False):
             # set analytics sample rate
             s.set_tag(ANALYTICS_SAMPLE_RATE_KEY, config.flask_cache.get_analytics_sample_rate())
             # add connection meta if there is one
-            client = _extract_client(self.cache, write=write)
+            client = _extract_client(self.cache)
             if client is not None:
                 try:
                     s.set_tags(_extract_conn_tags(client))
@@ -91,7 +97,7 @@ def set(self, *args, **kwargs):
             """
             Track ``set`` operation
             """
-            with self.__trace("flask_cache.cmd", write=True) as span:
+            with self.__trace("flask_cache.cmd") as span:
                 span.resource = _resource_from_cache_prefix("SET", self.config)
                 if len(args) > 0:
                     span.set_tag(COMMAND_KEY, args[0])
@@ -101,7 +107,7 @@ def add(self, *args, **kwargs):
             """
             Track ``add`` operation
             """
-            with self.__trace("flask_cache.cmd", write=True) as span:
+            with self.__trace("flask_cache.cmd") as span:
                 span.resource = _resource_from_cache_prefix("ADD", self.config)
                 if len(args) > 0:
                     span.set_tag(COMMAND_KEY, args[0])
@@ -111,7 +117,7 @@ def delete(self, *args, **kwargs):
             """
             Track ``delete`` operation
             """
-            with self.__trace("flask_cache.cmd", write=True) as span:
+            with self.__trace("flask_cache.cmd") as span:
                 span.resource = _resource_from_cache_prefix("DELETE", self.config)
                 if len(args) > 0:
                     span.set_tag(COMMAND_KEY, args[0])
@@ -121,7 +127,7 @@ def delete_many(self, *args, **kwargs):
             """
             Track ``delete_many`` operation
             """
-            with self.__trace("flask_cache.cmd", write=True) as span:
+            with self.__trace("flask_cache.cmd") as span:
                 span.resource = _resource_from_cache_prefix("DELETE_MANY", self.config)
                 span.set_tag(COMMAND_KEY, list(args))
                 return super(TracedCache, self).delete_many(*args, **kwargs)
@@ -130,7 +136,7 @@ def clear(self, *args, **kwargs):
             """
             Track ``clear`` operation
             """
-            with self.__trace("flask_cache.cmd", write=True) as span:
+            with self.__trace("flask_cache.cmd") as span:
                 span.resource = _resource_from_cache_prefix("CLEAR", self.config)
                 return super(TracedCache, self).clear(*args, **kwargs)
 
@@ -147,7 +153,7 @@ def set_many(self, *args, **kwargs):
             """
             Track ``set_many`` operation
             """
-            with self.__trace("flask_cache.cmd", write=True) as span:
+            with self.__trace("flask_cache.cmd") as span:
                 span.resource = _resource_from_cache_prefix("SET_MANY", self.config)
                 if len(args) > 0:
                     span.set_tag(COMMAND_KEY, list(args[0].keys()))

ddtrace/contrib/flask_cache/utils.py

@@ -17,14 +17,19 @@ def _resource_from_cache_prefix(resource, cache):
     return name.lower()
 
 
-def _extract_client(cache, write=False):
+def _extract_client(cache):
     """
     Get the client from the cache instance according to the current operation
     """
     client = getattr(cache, "_client", None)
     if client is None:
         # flask-caching has _read_clients & _write_client for the redis backend
-        client = getattr(cache, "_write_client" if write else "_read_clients", None)
+        # These use the same connection so just try to get a reference to one of them.
+        # flask-caching < 2.0.0 uses _read_clients so look for that one too.
+        for attr in ("_write_client", "_read_client", "_read_clients"):
+            client = getattr(cache, attr, None)
+            if client is not None:
+                break
     return client
 
 

releasenotes/notes/flask_caching-dc23b94171041b4f.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    flask_caching: fix redis tagging after the v2.0 release.