Core request id not override (#19759)

* not override request id if it already exists in header

* update

* changelog

sdk/core/azure-core/CHANGELOG.md

@@ -10,6 +10,7 @@
 
 ### Fixed
 
+- Not override "x-ms-client-request-id" if it already exists in the header.    #17757
 
 ## 1.16.0 (2021-07-01)
 

sdk/core/azure-core/azure/core/pipeline/policies/_universal.py

@@ -154,8 +154,12 @@ def on_request(self, request):
         elif self._request_id is None:
             return
         elif self._request_id is not _Unset:
+            if "x-ms-client-request-id" in request.http_request.headers:
+                return
             request_id = self._request_id
         elif self._auto_request_id:
+            if "x-ms-client-request-id" in request.http_request.headers:
+                return
             request_id = str(uuid.uuid1())
         if request_id is not unset:
             header = {"x-ms-client-request-id": request_id}

sdk/core/azure-core/tests/test_request_id_policy.py

@@ -54,3 +54,12 @@ def test_request_id_policy(auto_request_id, request_id_init, request_id_set, req
         assert request.headers["x-ms-client-request-id"] == "VALUE"
     else:
         assert not "x-ms-client-request-id" in request.headers
+
+def test_request_id_already_exists():
+    """Test policy with no other policy and happy path"""
+    request_id_policy = RequestIdPolicy()
+    request = HttpRequest('GET', 'http://127.0.0.1/')
+    request.headers["x-ms-client-request-id"] = "VALUE"
+    pipeline_request = PipelineRequest(request, PipelineContext(None))
+    request_id_policy.on_request(pipeline_request)
+    assert request.headers["x-ms-client-request-id"] == "VALUE"