Make gzip work with app that is generatorgzip_work_with_generator

```
$ tox
...
  py26: commands succeeded
  py27: commands succeeded
  py34: commands succeeded
  py35: commands succeeded
  pypy: commands succeeded
  congratulations :)
```

2 files changed, 60 insertions, 8 deletions

diff --git a/paste/gzipper.py b/paste/gzipper.py
index eca8775..5f59141 100644
--- a/paste/gzipper.py
+++ b/paste/gzipper.py
@@ -71,15 +71,18 @@ class GzipResponse(object):
         return [s]
 
     def finish_response(self, app_iter):
-        if self.compressible:
-            output = gzip.GzipFile(mode='wb', compresslevel=self.compress_level,
-                fileobj=self.buffer)
-        else:
-            output = self.buffer
+        output = None
+
         try:
             for s in app_iter:
+                if not output:
+                    if self.compressible:
+                        output = gzip.GzipFile(mode='wb', compresslevel=self.compress_level,
+                            fileobj=self.buffer)
+                    else:
+                        output = self.buffer
                 output.write(s)
-            if self.compressible:
+            if output and self.compressible:
                 output.close()
         finally:
             if hasattr(app_iter, 'close'):
diff --git a/tests/test_gzipper.py b/tests/test_gzipper.py
index 54b7901..8ad5ec3 100644
--- a/tests/test_gzipper.py
+++ b/tests/test_gzipper.py
@@ -3,17 +3,66 @@ from paste.gzipper import middleware
 import gzip
 import six
 
+
 def simple_app(environ, start_response):
     start_response('200 OK', [('content-type', 'text/plain')])
     return [b'this is a test']
 
-wsgi_app = middleware(simple_app)
-app = TestApp(wsgi_app)
+
+def simple_app_nothing(environ, start_response):
+    start_response('200 OK', [('content-type', 'text/plain')])
+    return [b'']
+
+
+def simple_app_generator(environ, start_response):
+    start_response('200 OK', [('content-type', 'text/plain')])
+    yield b'this is a test'
+
+
+def simple_app_generator_nothing(environ, start_response):
+    start_response('200 OK', [('content-type', 'text/plain')])
+    yield b''
+
 
 def test_gzip():
+    wsgi_app = middleware(simple_app)
+    app = TestApp(wsgi_app)
+    res = app.get(
+        '/', extra_environ=dict(HTTP_ACCEPT_ENCODING='gzip'))
+    assert int(res.header('content-length')) == len(res.body)
+    assert res.body != b'this is a test'
+    actual = gzip.GzipFile(fileobj=six.BytesIO(res.body)).read()
+    assert actual == b'this is a test'
+
+
+def test_gzip_nothing():
+    wsgi_app = middleware(simple_app_nothing)
+    app = TestApp(wsgi_app)
+    res = app.get(
+        '/', extra_environ=dict(HTTP_ACCEPT_ENCODING='gzip'))
+    assert int(res.header('content-length')) == len(res.body)
+    assert res.body != b'this is a test'
+    actual = gzip.GzipFile(fileobj=six.BytesIO(res.body)).read()
+    assert actual == b''
+
+
+def test_gzip_generator():
+    wsgi_app = middleware(simple_app_generator)
+    app = TestApp(wsgi_app)
     res = app.get(
         '/', extra_environ=dict(HTTP_ACCEPT_ENCODING='gzip'))
     assert int(res.header('content-length')) == len(res.body)
     assert res.body != b'this is a test'
     actual = gzip.GzipFile(fileobj=six.BytesIO(res.body)).read()
     assert actual == b'this is a test'
+
+
+def test_gzip_generator_nothing():
+    wsgi_app = middleware(simple_app_generator_nothing)
+    app = TestApp(wsgi_app)
+    res = app.get(
+        '/', extra_environ=dict(HTTP_ACCEPT_ENCODING='gzip'))
+    assert int(res.header('content-length')) == len(res.body)
+    assert res.body != b'this is a test'
+    actual = gzip.GzipFile(fileobj=six.BytesIO(res.body)).read()
+    assert actual == b''