Move DD code into its own directory (#6)

reference/ddtrace/filters.py

@@ -0,0 +1,49 @@
+import re
+
+from .ext import http
+
+
+class FilterRequestsOnUrl(object):
+    r"""Filter out traces from incoming http requests based on the request's url.
+
+    This class takes as argument a list of regular expression patterns
+    representing the urls to be excluded from tracing. A trace will be excluded
+    if its root span contains a ``http.url`` tag and if this tag matches any of
+    the provided regular expression using the standard python regexp match
+    semantic (https://docs.python.org/2/library/re.html#re.match).
+
+    :param list regexps: a list of regular expressions (or a single string) defining
+                         the urls that should be filtered out.
+
+    Examples:
+    To filter out http calls to domain api.example.com::
+
+        FilterRequestsOnUrl(r'http://api\\.example\\.com')
+
+    To filter out http calls to all first level subdomains from example.com::
+
+        FilterRequestOnUrl(r'http://.*+\\.example\\.com')
+
+    To filter out calls to both http://test.example.com and http://example.com/healthcheck::
+
+        FilterRequestOnUrl([r'http://test\\.example\\.com', r'http://example\\.com/healthcheck'])
+    """
+    def __init__(self, regexps):
+        if isinstance(regexps, str):
+            regexps = [regexps]
+        self._regexps = [re.compile(regexp) for regexp in regexps]
+
+    def process_trace(self, trace):
+        """
+        When the filter is registered in the tracer, process_trace is called by
+        on each trace before it is sent to the agent, the returned value will
+        be fed to the next filter in the list. If process_trace returns None,
+        the whole trace is discarded.
+        """
+        for span in trace:
+            if span.parent_id is None and span.get_tag(http.URL) is not None:
+                url = span.get_tag(http.URL)
+                for regexp in self._regexps:
+                    if regexp.match(url):
+                        return None
+        return trace