api: simplify _put codepath

The length is always provided and should be included in every request, so make
it mandatory.

Move the header name variable to the local API class, making it overridable by
a subclass — you never know!

Author: jd

ddtrace/api.py

@@ -13,7 +13,6 @@
 
 log = get_logger(__name__)
 
-TRACE_COUNT_HEADER = 'X-Datadog-Trace-Count'
 
 _VERSIONS = {'v0.4': {'traces': '/v0.4/traces',
                       'services': '/v0.4/services',
@@ -100,6 +99,9 @@ class API(object):
     """
     Send data to the trace agent using the HTTP protocol and JSON format
     """
+
+    TRACE_COUNT_HEADER = 'X-Datadog-Trace-Count'
+
     def __init__(self, hostname, port, headers=None, encoder=None, priority_sampling=False):
         self.hostname = hostname
         self.port = int(port)
@@ -169,14 +171,12 @@ def send_traces(self, traces):
     def send_services(self, *args, **kwargs):
         return
 
-    def _put(self, endpoint, data, count=0):
+    def _put(self, endpoint, data, count):
+        headers = self._headers.copy()
+        headers[self.TRACE_COUNT_HEADER] = str(count)
+
         conn = httplib.HTTPConnection(self.hostname, self.port)
         try:
-            headers = self._headers
-            if count:
-                headers = dict(self._headers)
-                headers[TRACE_COUNT_HEADER] = str(count)
-
             conn.request('PUT', endpoint, data, headers)
 
             # Parse the HTTPResponse into an API.Response