Avoid any body when request is a HEAD request

Instead of creating a body for a request that is known
to be a HEAD request avoid creating any body in the first
place and just return the status code determined from
the health evaluation.

Closes-Bug: #1494533

Change-Id: I39abee3cdfff4af40355f91d22607e3a2aa52e29

2 files changed, 53 insertions, 9 deletions

diff --git a/oslo_middleware/healthcheck/__init__.py b/oslo_middleware/healthcheck/__init__.py
index 9aa2c2e..4a17295 100644
--- a/oslo_middleware/healthcheck/__init__.py
+++ b/oslo_middleware/healthcheck/__init__.py
@@ -54,6 +54,22 @@ class Healthcheck(base.ConfigurableMiddleware):
        can provide details (or no details, depending on if configured) about
        the activity of the server.
 
+    Example requests/responses:
+
+        $ curl -i -X HEAD "http://0.0.0.0:8775/status"
+        HTTP/1.1 204 No Content
+        Content-Type: text/plain; charset=UTF-8
+        Content-Length: 0
+        Date: Fri, 11 Sep 2015 18:55:08 GMT
+
+        $ curl -i  "http://0.0.0.0:8775/status"
+        HTTP/1.1 200 OK
+        Content-Type: text/plain; charset=UTF-8
+        Content-Length: 2
+        Date: Fri, 11 Sep 2015 18:55:43 GMT
+
+        OK
+
     Example of paste configuration:
 
     .. code-block:: ini
@@ -101,6 +117,10 @@ class Healthcheck(base.ConfigurableMiddleware):
         True: webob.exc.HTTPOk.code,
         False: webob.exc.HTTPServiceUnavailable.code,
     }
+    HEAD_HEALTHY_TO_STATUS_CODES = {
+        True: webob.exc.HTTPNoContent.code,
+        False: webob.exc.HTTPServiceUnavailable.code,
+    }
     PLAIN_RESPONSE_TEMPLATE = """
 {% for reason in reasons %}
 {% if reason %}{{reason}}{% endif -%}
@@ -198,6 +218,9 @@ class Healthcheck(base.ConfigurableMiddleware):
             }
         return (self._pretty_json_dumps(body), 'application/json')
 
+    def _make_head_response(self, results, healthy):
+        return ( "", "text/plain")
+
     def _make_html_response(self, results, healthy):
         try:
             hostname = socket.gethostname()
@@ -225,11 +248,15 @@ class Healthcheck(base.ConfigurableMiddleware):
             return None
         results = [ext.obj.healthcheck() for ext in self._backends]
         healthy = self._are_results_healthy(results)
-        accept_type = req.accept.best_match(self._accept_order)
-        if not accept_type:
-            accept_type = self._default_accept
-        functor = self._accept_to_functor[accept_type]
+        if req.method == "HEAD":
+            functor = self._make_head_response
+            status = self.HEAD_HEALTHY_TO_STATUS_CODES[healthy]
+        else:
+            status = self.HEALTHY_TO_STATUS_CODES[healthy]
+            accept_type = req.accept.best_match(self._accept_order)
+            if not accept_type:
+                accept_type = self._default_accept
+            functor = self._accept_to_functor[accept_type]
         body, content_type = functor(results, healthy)
-        status = self.HEALTHY_TO_STATUS_CODES[healthy]
         return webob.response.Response(status=status, body=body,
                                        content_type=content_type)
diff --git a/oslo_middleware/tests/test_healthcheck.py b/oslo_middleware/tests/test_healthcheck.py
index b516d0c..144d274 100644
--- a/oslo_middleware/tests/test_healthcheck.py
+++ b/oslo_middleware/tests/test_healthcheck.py
@@ -29,16 +29,18 @@ class HealthcheckTests(test_base.BaseTestCase):
         return 'Hello, World!!!'
 
     def _do_test_request(self, conf={}, path='/healthcheck',
-                         accept='text/plain'):
+                         accept='text/plain', method='GET'):
         self.app = healthcheck.Healthcheck(self.application, conf)
-        req = webob.Request.blank(path, accept=accept)
+        req = webob.Request.blank(path, accept=accept, method=method)
         res = req.get_response(self.app)
         return res
 
     def _do_test(self, conf={}, path='/healthcheck',
                  expected_code=webob.exc.HTTPOk.code,
-                 expected_body=b'', accept='text/plain'):
-        res = self._do_test_request(conf=conf, path=path, accept=accept)
+                 expected_body=b'', accept='text/plain',
+                 method='GET'):
+        res = self._do_test_request(conf=conf, path=path,
+                                    accept=accept, method=method)
         self.assertEqual(expected_code, res.status_int)
         self.assertEqual(expected_body, res.body)
 
@@ -74,6 +76,12 @@ class HealthcheckTests(test_base.BaseTestCase):
         self._do_test(conf, expected_body=b'OK')
         self.assertIn('disable_by_file', self.app._backends.names())
 
+    def test_disablefile_enabled_head(self):
+        conf = {'backends': 'disable_by_file',
+                'disable_by_file_path': '/foobar'}
+        self._do_test(conf, expected_body=b'', method='HEAD',
+                      expected_code=webob.exc.HTTPNoContent.code)
+
     def test_disablefile_enabled_html_detailed(self):
         conf = {'backends': 'disable_by_file',
                 'disable_by_file_path': '/foobar', 'detailed': True}
@@ -91,6 +99,15 @@ class HealthcheckTests(test_base.BaseTestCase):
                       expected_body=b'DISABLED BY FILE')
         self.assertIn('disable_by_file', self.app._backends.names())
 
+    def test_disablefile_disabled_head(self):
+        filename = self.create_tempfiles([('test', 'foobar')])[0]
+        conf = {'backends': 'disable_by_file',
+                'disable_by_file_path': filename}
+        self._do_test(conf,
+                      expected_code=webob.exc.HTTPServiceUnavailable.code,
+                      expected_body=b'', method='HEAD')
+        self.assertIn('disable_by_file', self.app._backends.names())
+
     def test_disablefile_disabled_html_detailed(self):
         filename = self.create_tempfiles([('test', 'foobar')])[0]
         conf = {'backends': 'disable_by_file',