AMLII-1086 fix stale client_transport tag (#802)

initialize reassigns socket_path property on the global statsd
instance, but the client_transport tag was computed in the constructor
and never updated, causing client to misreport transport as udp when a
unix socket was actually used.

This patch makes the tag dynamic and updates it every time the
socket_path property is updated.

datadog/dogstatsd/base.py

@@ -325,14 +325,12 @@ def __init__(
             self.socket_path = socket_path  # type: Optional[text]
             self.host = None
             self.port = None
-            transport = "uds"
             if not self._max_payload_size:
                 self._max_payload_size = UDS_OPTIMAL_PAYLOAD_LENGTH
         else:
             self.socket_path = None
             self.host = self.resolve_host(host, use_default_route)
             self.port = int(port)
-            transport = "udp"
             if not self._max_payload_size:
                 self._max_payload_size = UDP_OPTIMAL_PAYLOAD_LENGTH
 
@@ -381,7 +379,6 @@ def __init__(
         self._client_tags = [
             "client:py",
             "client_version:{}".format(__version__),
-            "client_transport:{}".format(transport),
         ]
         self._reset_telemetry()
         self._telemetry_flush_interval = telemetry_min_flush_interval
@@ -417,6 +414,15 @@ def __init__(
         if not disable_background_sender:
             self.enable_background_sender(sender_queue_size, sender_queue_timeout)
 
+    @property
+    def socket_path(self):
+        return self._socket_path
+
+    @socket_path.setter
+    def socket_path(self, path):
+        self._socket_path = path
+        self._transport = "udp" if path is None else "uds"
+
     def enable_background_sender(self, sender_queue_size=0, sender_queue_timeout=0):
         """
         Use a background thread to communicate with the dogstatsd server.
@@ -943,7 +949,10 @@ def bytes_dropped(self):
         return self.bytes_dropped_queue + self.bytes_dropped_writer
 
     def _flush_telemetry(self):
-        telemetry_tags = ",".join(self._add_constant_tags(self._client_tags))
+        tags = self._client_tags[:]
+        tags.append("client_transport:{}".format(self._transport))
+        tags.extend(self.constant_tags)
+        telemetry_tags = ",".join(tags)
 
         return TELEMETRY_FORMATTING_STR % (
             self.metrics_count,

tests/unit/dogstatsd/test_statsd.py

@@ -145,9 +145,9 @@ def tearDown(self):
         """
         self._procfs_mock.stop()
 
-    def assert_equal_telemetry(self, expected_payload, actual_payload, telemetry=None):
+    def assert_equal_telemetry(self, expected_payload, actual_payload, telemetry=None, **kwargs):
         if telemetry is None:
-            telemetry = telemetry_metrics(bytes_sent=len(expected_payload))
+            telemetry = telemetry_metrics(bytes_sent=len(expected_payload), **kwargs)
 
         if expected_payload:
             expected_payload = "\n".join([expected_payload, telemetry])
@@ -705,6 +705,14 @@ def test_udp_socket_ensures_min_receive_buffer(self, mock_socket_create):
             MIN_SEND_BUFFER_SIZE,
         )
 
+    def test_socket_path_updates_telemetry(self):
+        self.statsd.gauge("foo", 1)
+        self.assert_equal_telemetry("foo:1|g\n", self.recv(2), transport="udp")
+        self.statsd.socket_path = "/fake/path"
+        self.statsd._reset_telemetry()
+        self.statsd.gauge("foo", 2)
+        self.assert_equal_telemetry("foo:2|g\n", self.recv(2), transport="uds")
+
     def test_distributed(self):
         """
         Measure the distribution of a function's run time using distribution custom metric.