Add http.referrer_host tag

Author: cgcote

ddtrace/contrib/internal/trace_utils.py

@@ -172,6 +172,27 @@ def _get_request_header_user_agent(headers, headers_are_case_sensitive=False):
     return ""
 
 
+def _get_request_header_referer_host(headers, headers_are_case_sensitive=False):
+    # type: (Mapping[str, str], bool) -> str
+    """Get referer host from request headers
+    :param headers: A dict of http headers to be stored in the span
+    :type headers: dict or list
+    :param headers_are_case_sensitive: Whether the headers are case sensitive
+    :type headers_are_case_sensitive: bool
+    :return: The referer host if found, empty string otherwise
+    :rtype: str
+    """
+    referer = _get_header_value_case_insensitive(headers, "referer") if headers_are_case_sensitive else headers.get("referer")
+    if referer:
+        try:
+            parsed_url = parse.urlparse(referer)
+            if parsed_url.netloc:
+                return parsed_url.netloc
+        except Exception:
+            log.debug("failed to parse referer header value: %r", referer)
+    return ""
+
+
 def _get_request_header_client_ip(headers, peer_ip=None, headers_are_case_sensitive=False):
     # type: (Optional[Mapping[str, str]], Optional[str], bool) -> str
 
@@ -501,6 +522,11 @@ def set_http_meta(
         if user_agent:
             span.set_tag_str(http.USER_AGENT, user_agent)
 
+        # Extract referrer host if referer header is present
+        referer_host = _get_request_header_referer_host(request_headers, headers_are_case_sensitive)
+        if referer_host:
+            span.set_tag_str(http.REFERRER_HOST, referer_host)
+
         # We always collect the IP if appsec is enabled to report it on potential vulnerabilities.
         # https://datadoghq.atlassian.net/wiki/spaces/APS/pages/2118779066/Client+IP+addresses+resolution
         if asm_config._asm_enabled or config._retrieve_client_ip:

ddtrace/ext/http.py

@@ -17,6 +17,7 @@
 VERSION = "http.version"
 CLIENT_IP = "http.client_ip"
 ROUTE = "http.route"
+REFERRER_HOST = "http.referrer_host"
 
 # template render span type
 TEMPLATE = "template"

tests/tracer/test_trace_utils.py

@@ -252,6 +252,38 @@ def test_whitelist_case_insensitive(self, span, integration_config):
         )
         assert span.get_tag("http.response.headers.content-type") == "some;value"
 
+    def test_referer_host_extraction(self, span, integration_config):
+        """Test that referer host is correctly extracted from referer header"""
+        headers = {
+            "referer": "https://example.com/path?query=1",
+        }
+        trace_utils.set_http_meta(span, integration_config, request_headers=headers)
+        assert span.get_tag("http.referrer_host") == "example.com"
+
+    def test_referer_host_case_insensitive(self, span, integration_config):
+        """Test that referer host extraction works with case-insensitive header names"""
+        headers = {
+            "Referer": "https://example.com/path?query=1",
+        }
+        trace_utils.set_http_meta(span, integration_config, request_headers=headers, headers_are_case_sensitive=True)
+        assert span.get_tag("http.referrer_host") == "example.com"
+
+    def test_referer_host_missing(self, span, integration_config):
+        """Test that no referer host tag is set when referer header is missing"""
+        headers = {
+            "other-header": "value",
+        }
+        trace_utils.set_http_meta(span, integration_config, request_headers=headers)
+        assert span.get_tag("http.referrer_host") is None
+
+    def test_referer_host_invalid_url(self, span, integration_config):
+        """Test that no referer host tag is set when referer URL is invalid"""
+        headers = {
+            "referer": "not-a-valid-url",
+        }
+        trace_utils.set_http_meta(span, integration_config, request_headers=headers)
+        assert span.get_tag("http.referrer_host") is None
+
 
 @pytest.mark.parametrize(
     "pin,config_val,default,global_service,expected",