Allow compatibility headers for request_id

We discovered that Nova is using a local version of the request_id
header code because it's x-compute-request-id predates
x-openstack-request-id, and things were never migrated after the oslo
code was extracted. In order to let Nova use the base code (which may
become more complicated with inbound request-id setting) we need to
support a compat headers field, which is additional http header names
that should be set with the request-id value.

Change-Id: I18a92f8bf2f85fcf30d32be68bae58f64b135df0

3 files changed, 45 insertions, 2 deletions

diff --git a/oslo_middleware/request_id.py b/oslo_middleware/request_id.py
index 31a433b..5716c82 100644
--- a/oslo_middleware/request_id.py
+++ b/oslo_middleware/request_id.py
@@ -30,11 +30,21 @@ class RequestId(base.ConfigurableMiddleware):
     request environment. The request ID is also added to API response.
     """
 
+    # if compat_headers is set, we also return the request_id in those
+    # headers as well. This allows projects like Nova to adopt
+    # oslo.middleware without impacting existing users.
+    compat_headers = []
+
     @webob.dec.wsgify
     def __call__(self, req):
         req_id = context.generate_request_id()
         req.environ[ENV_REQUEST_ID] = req_id
         response = req.get_response(self.application)
-        if HTTP_RESP_HEADER_REQUEST_ID not in response.headers:
-            response.headers.add(HTTP_RESP_HEADER_REQUEST_ID, req_id)
+
+        return_headers = [HTTP_RESP_HEADER_REQUEST_ID]
+        return_headers.extend(self.compat_headers)
+
+        for header in return_headers:
+            if header not in response.headers:
+                response.headers.add(header, req_id)
         return response
diff --git a/oslo_middleware/tests/test_request_id.py b/oslo_middleware/tests/test_request_id.py
index 039b7af..5c79c21 100644
--- a/oslo_middleware/tests/test_request_id.py
+++ b/oslo_middleware/tests/test_request_id.py
@@ -22,6 +22,10 @@ import webob.dec
 from oslo_middleware import request_id
 
 
+class AltHeader(request_id.RequestId):
+    compat_headers = ["x-compute-req-id", "x-silly-id"]
+
+
 class RequestIdTest(test_base.BaseTestCase):
     def test_generate_request_id(self):
         @webob.dec.wsgify
@@ -37,3 +41,25 @@ class RequestIdTest(test_base.BaseTestCase):
         self.assertThat(res_req_id, matchers.StartsWith('req-'))
         # request-id in request environ is returned as response body
         self.assertEqual(res.body.decode('utf-8'), res_req_id)
+
+    def test_compat_headers(self):
+        """Test that compat headers are set
+
+        Compat headers might exist on a super class to support
+        previous API contracts. This ensures that you can set that to
+        a list of headers and those values are the same as the
+        request_id.
+
+        """
+        @webob.dec.wsgify
+        def application(req):
+            return req.environ[request_id.ENV_REQUEST_ID]
+
+        app = AltHeader(application)
+        req = webob.Request.blank('/test')
+        res = req.get_response(app)
+
+        res_req_id = res.headers.get(request_id.HTTP_RESP_HEADER_REQUEST_ID)
+
+        self.assertEqual(res.headers.get("x-compute-req-id"), res_req_id)
+        self.assertEqual(res.headers.get("x-silly-id"), res_req_id)
diff --git a/releasenotes/notes/compat_headers-55a635b8ec01b6f1.yaml b/releasenotes/notes/compat_headers-55a635b8ec01b6f1.yaml
new file mode 100644
index 0000000..489b33c
--- /dev/null
+++ b/releasenotes/notes/compat_headers-55a635b8ec01b6f1.yaml
@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    This adds a new ``compat_headers`` class attribute to the
+    ``RequestId`` middleware. That allows projects like Nova that have
+    API contracts on alternative request-id headers to adopt the oslo
+    ``RequestId`` middleware but still retain their API contract.