[encoder] downgrade the communication format and API, if the new endpoint is not available

Author: Emanuele Palazzetti

ddtrace/api.py

@@ -3,7 +3,7 @@
 import time
 
 # project
-from .encoding import get_encoder
+from .encoding import get_encoder, JSONEncoder
 from .compat import httplib
 
 
@@ -14,43 +14,65 @@ class API(object):
     """
     Send data to the trace agent using the HTTP protocol and JSON format
     """
-    def __init__(self, hostname, port, wait_response=False, headers=None, encoder=None):
+    def __init__(self, hostname, port, headers=None, encoder=None):
         self.hostname = hostname
         self.port = port
+        self._traces = '/v0.3/traces'
+        self._services = '/v0.3/services'
         self._encoder = encoder or get_encoder()
-        self._wait_response = wait_response
 
         # overwrite the Content-type with the one chosen in the Encoder
         self._headers = headers or {}
         self._headers.update({'Content-Type': self._encoder.content_type})
 
+    def _downgrade(self):
+        """
+        Downgrades the used encoder and API level. This method must
+        fallback to a safe encoder and API, so that it will success
+        despite users' configuration
+        """
+        self._traces = '/v0.2/traces'
+        self._services = '/v0.2/services'
+        self._encoder = JSONEncoder()
+        self._headers.update({'Content-Type': self._encoder.content_type})
+
     def send_traces(self, traces):
         if not traces:
             return
         start = time.time()
         data = self._encoder.encode_traces(traces)
-        response = self._send_span_data(data)
+        response = self._put(self._traces, data)
+
+        # the API endpoint is not available so we should
+        # downgrade the connection and re-try the call
+        if response.status == 404:
+            log.debug('calling the endpoint "%s" but received 404; downgrading the API', self._traces)
+            self._downgrade()
+            return self.send_traces(traces)
+
         log.debug("reported %d spans in %.5fs", len(traces), time.time() - start)
         return response
 
     def send_services(self, services):
         if not services:
             return
-        log.debug("Reporting %d services", len(services))
         s = {}
         for service in services:
             s.update(service)
         data = self._encoder.encode_services(s)
-        return self._put("/v0.3/services", data)
+        response = self._put(self._services, data)
 
-    def _send_span_data(self, data):
-        return self._put("/v0.3/traces", data)
+        # the API endpoint is not available so we should
+        # downgrade the connection and re-try the call
+        if response.status == 404:
+            log.debug('calling the endpoint "%s" but received 404; downgrading the API', self._services)
+            self._downgrade()
+            return self.send_services(services)
+
+        log.debug("reported %d services", len(services))
+        return response
 
     def _put(self, endpoint, data):
         conn = httplib.HTTPConnection(self.hostname, self.port)
         conn.request("PUT", endpoint, data, self._headers)
-
-        # read the server response only if the
-        # API object is configured to do so
-        if self._wait_response:
-            return conn.getresponse()
+        return conn.getresponse()

tests/test_integration.py

@@ -161,8 +161,8 @@ def setUp(self):
         """
         # create a new API object to test the transport using synchronous calls
         self.tracer = get_dummy_tracer()
-        self.api_json = API('localhost', 7777, wait_response=True, encoder=JSONEncoder())
-        self.api_msgpack = API('localhost', 7777, wait_response=True, encoder=MsgpackEncoder())
+        self.api_json = API('localhost', 7777, encoder=JSONEncoder())
+        self.api_msgpack = API('localhost', 7777, encoder=MsgpackEncoder())
 
     def test_send_single_trace(self):
         # register a single trace with a span and send them to the trace agent