commit 0d2604c110828af0fc7fcf423ecfac554669c404
Author: Tim Burke <tim.burke@gmail.com>
Date:   Fri Oct 2 16:41:21 2020 -0700

    wsgi: Ensure _response_headers is a list
    
    It's reasonably common that apps or middlewares may send back headers
    via dict.items(), but WSGIContext users often expect the headers to be
    a list.  Convert it for them, to avoid errors like
    
        AttributeError: 'dict_items' object has no attribute 'append'
    
    Change-Id: I4d061fad4da370c1cbb77ab78a55133319ea2dd7

diff --git a/swift/common/wsgi.py b/swift/common/wsgi.py
index 11fcaa4..0fe2837 100644
--- a/swift/common/wsgi.py
+++ b/swift/common/wsgi.py
@@ -1314,7 +1314,8 @@ class WSGIContext(object):
         Uses the same semantics as the usual WSGI start_response.
         """
         self._response_status = status
-        self._response_headers = headers
+        self._response_headers = \
+            headers if isinstance(headers, list) else list(headers)
         self._response_exc_info = exc_info
 
     def _app_call(self, env):
diff --git a/test/unit/common/test_wsgi.py b/test/unit/common/test_wsgi.py
index cb489dd..0d783f2 100644
--- a/test/unit/common/test_wsgi.py
+++ b/test/unit/common/test_wsgi.py
@@ -1671,29 +1671,29 @@ class TestWSGIContext(unittest.TestCase):
 
         def app(env, start_response):
             start_response(statuses.pop(0), [('Content-Length', '3')])
-            yield 'Ok\n'
+            yield b'Ok\n'
 
         wc = wsgi.WSGIContext(app)
         r = Request.blank('/')
         it = wc._app_call(r.environ)
         self.assertEqual(wc._response_status, '200 Ok')
-        self.assertEqual(''.join(it), 'Ok\n')
+        self.assertEqual(b''.join(it), b'Ok\n')
         r = Request.blank('/')
         it = wc._app_call(r.environ)
         self.assertEqual(wc._response_status, '404 Not Found')
-        self.assertEqual(''.join(it), 'Ok\n')
+        self.assertEqual(b''.join(it), b'Ok\n')
 
     def test_app_iter_is_closable(self):
 
         def app(env, start_response):
-            yield ''
-            yield ''
+            yield b''
+            yield b''
             start_response('200 OK', [('Content-Length', '25')])
-            yield 'aaaaa'
-            yield 'bbbbb'
-            yield 'ccccc'
-            yield 'ddddd'
-            yield 'eeeee'
+            yield b'aaaaa'
+            yield b'bbbbb'
+            yield b'ccccc'
+            yield b'ddddd'
+            yield b'eeeee'
 
         wc = wsgi.WSGIContext(app)
         r = Request.blank('/')
@@ -1701,8 +1701,8 @@ class TestWSGIContext(unittest.TestCase):
         self.assertEqual(wc._response_status, '200 OK')
 
         iterator = iter(iterable)
-        self.assertEqual('aaaaa', next(iterator))
-        self.assertEqual('bbbbb', next(iterator))
+        self.assertEqual(b'aaaaa', next(iterator))
+        self.assertEqual(b'bbbbb', next(iterator))
         iterable.close()
         with self.assertRaises(StopIteration):
             next(iterator)
@@ -1712,16 +1712,34 @@ class TestWSGIContext(unittest.TestCase):
 
         def app(env, start_response):
             start_response(statuses.pop(0), [('Content-Length', '30')])
-            yield 'Ok\n'
+            yield b'Ok\n'
 
         wc = wsgi.WSGIContext(app)
         r = Request.blank('/')
         it = wc._app_call(r.environ)
         wc.update_content_length(35)
         self.assertEqual(wc._response_status, '200 Ok')
-        self.assertEqual(''.join(it), 'Ok\n')
+        self.assertEqual(b''.join(it), b'Ok\n')
         self.assertEqual(wc._response_headers, [('Content-Length', '35')])
 
+    def test_app_returns_headers_as_dict_items(self):
+        statuses = ['200 Ok']
+
+        def app(env, start_response):
+            start_response(statuses.pop(0), {'Content-Length': '3'}.items())
+            yield b'Ok\n'
+
+        wc = wsgi.WSGIContext(app)
+        r = Request.blank('/')
+        it = wc._app_call(r.environ)
+        wc._response_headers.append(('X-Trans-Id', 'txn'))
+        self.assertEqual(wc._response_status, '200 Ok')
+        self.assertEqual(b''.join(it), b'Ok\n')
+        self.assertEqual(wc._response_headers, [
+            ('Content-Length', '3'),
+            ('X-Trans-Id', 'txn'),
+        ])
+
 
 class TestPipelineWrapper(unittest.TestCase):