feat(flask): store request headers

.github/PULL_REQUEST_TEMPLATE/integration.md

@@ -27,3 +27,4 @@ This PR adds support for [`<integration>`](<!--link to relevant integration docs
 - [ ] 500-level responses are tagged as errors
 - [ ] Async (if applicable)
   - [ ] Span parenting behaves as expected.
+- [ ] Request headers specified in the config are stored

ddtrace/contrib/flask/middleware.py

@@ -3,6 +3,8 @@
 from ...internal.logger import get_logger
 from ...propagation.http import HTTPPropagator
 from ...utils.deprecation import deprecated
+from ddtrace.http import store_request_headers
+from ddtrace import config
 
 import flask.templating
 from flask import g, request, signals
@@ -155,6 +157,7 @@ def _finish_span(self, span, exception=None):
         endpoint = ''
         url = ''
         if request:
+            store_request_headers(request.headers, span, config.flask)
             method = request.method
             endpoint = request.endpoint or code
             url = request.base_url or ''

releasenotes/notes/feature-flask-4bdb2b839fada0fb.yaml

@@ -0,0 +1,4 @@
+---
+features:
+  - |
+    Store request headers in Flask integration.

tests/contrib/flask/test_middleware.py

@@ -7,6 +7,7 @@
 from ddtrace.contrib.flask import TraceMiddleware
 from ddtrace.constants import SAMPLING_PRIORITY_KEY
 from ddtrace.ext import http, errors
+from ddtrace import config
 
 from tests.opentracer.utils import init_tracer
 from .web import create_app
@@ -385,3 +386,17 @@ def test_success_200_ot(self):
         assert dd_span.error == 0
         assert_span_http_status_code(dd_span, 200)
         assert dd_span.meta.get(http.METHOD) == 'GET'
+
+    def test_http_request_header_tracing(self):
+        config.flask.http.trace_headers(['Host', 'my-header'])
+        self.app.get('/', headers={
+            'my-header': 'my_value',
+        })
+        traces = self.tracer.writer.pop_traces()
+
+        assert len(traces) == 1
+        assert len(traces[0]) == 1
+        span = traces[0][0]
+
+        assert span.get_tag('http.request.headers.my-header') == 'my_value'
+        assert span.get_tag('http.request.headers.host') == 'localhost'