Adds Reponse.has_body.

Purpose of this property is to allow users to check if the Response has
a body without forcing an evaulation of the underlying app_iter.
This is handy if you wan't to create a streaming response where the
app_iter itself is lazy (i.e. streams data over a socket) or the app_iter
can only read once.

2 files changed, 49 insertions, 0 deletions

diff --git a/tests/test_response.py b/tests/test_response.py
index 58fee3c..aaac831 100644
--- a/tests/test_response.py
+++ b/tests/test_response.py
@@ -437,6 +437,37 @@ def test_app_iter_range_inner_method():
     res = Response(app_iter=FakeAppIter())
     assert res.app_iter_range(30, 40), ('you win', 30 == 40)
 
+def test_has_body():
+    empty = Response()
+    assert not empty.has_body
+
+    with_list = Response(app_iter=['1'])
+    assert with_list.has_body
+
+    with_empty_list = Response(app_iter=[b''])
+    assert not with_empty_list.has_body
+
+    with_body = Response(body='Seomthing')
+    assert with_body.has_body
+
+    with_none_app_iter = Response(app_iter=None)
+    assert not with_none_app_iter.has_body
+
+    with_none_body = Response(body=None)
+    assert not with_none_body.has_body
+
+    # key feature: has_body should not read app_iter
+    app_iter = iter(['1', '2'])
+    not_iterating = Response(app_iter=app_iter)
+    assert not_iterating.has_body
+    assert next(app_iter) == '1'
+
+    # messed with private attribute but method should nonetheless not
+    # return True
+    messing_with_privates = Response()
+    messing_with_privates._app_iter = None
+    assert not messing_with_privates.has_body
+
 def test_content_type_in_headerlist():
     # Couldn't manage to clone Response in order to modify class
     # attributes safely. Shouldn't classes be fresh imported for every
diff --git a/webob/response.py b/webob/response.py
index 1cc41cd..4faaad4 100644
--- a/webob/response.py
+++ b/webob/response.py
@@ -405,6 +405,24 @@ class Response(object):
 
     json = json_body = property(_json_body__get, _json_body__set, _json_body__del)
 
+    def _has_body__get(self):
+        """Determine if the the response has a body. In contrast to simply
+        accessing ``body`` this method will *not* read the underlying app_iter."""
+        app_iter = self._app_iter
+
+        if isinstance(app_iter, list) and len(app_iter) == 1:
+            if app_iter[0] != b'':
+                return True
+            else:
+                return False
+
+        if app_iter is None:  # pragma: no cover (just a safeguard, houl)
+            return False
+
+        return True
+
+    has_body = property(_has_body__get)
+
 
     #
     # text, unicode_body, ubody