Bugfix: wsgi.file_wrapper should pass-through seek/tell attrs

CHANGES.txt

@@ -11,6 +11,13 @@ Python Version Support
 Bugfix
 ~~~~~~
 
+- ``wsgi.file_wrapper`` now sets the ``seekable``, ``seek``, and ``tell`` attributes from
+  the underlying file if the underlying file is seekable. This allows WSGI
+  middleware to implement things like range requests for example
+
+  See https://github.com/Pylons/waitress/issues/359 and
+  https://github.com/Pylons/waitress/pull/363
+
 - In Python 3 ``OSError`` is no longer subscriptable, this caused failures on
   Windows attempting to loop to find an socket that would work for use in the
   trigger.

src/waitress/buffers.py

@@ -145,6 +145,16 @@ def __init__(self, file, block_size=32768):
         self.file = file
         self.block_size = block_size  # for __iter__
 
+        # This is for the benefit of anyone that is attempting to wrap this
+        # wsgi.file_wrapper in a WSGI middleware and wants to seek, this is
+        # useful for instance for support Range requests
+        if _is_seekable(self.file):
+            if hasattr(self.file, "seekable"):
+                self.seekable = self.file.seekable
+
+            self.seek = self.file.seek
+            self.tell = self.file.tell
+
     def prepare(self, size=None):
         if _is_seekable(self.file):
             start_pos = self.file.tell()

tests/test_buffers.py

@@ -185,6 +185,8 @@ def tearDown(self):
     def test_prepare_not_seekable(self):
         f = KindaFilelike(b"abc")
         inst = self._makeOne(f)
+        self.assertFalse(hasattr(inst, "seek"))
+        self.assertFalse(hasattr(inst, "tell"))
         result = inst.prepare()
         self.assertEqual(result, False)
         self.assertEqual(inst.remain, 0)
@@ -200,6 +202,8 @@ def test_prepare_not_seekable_closeable(self):
     def test_prepare_seekable_closeable(self):
         f = Filelike(b"abc", close=1, tellresults=[0, 10])
         inst = self._makeOne(f)
+        self.assertEqual(inst.seek, f.seek)
+        self.assertEqual(inst.tell, f.tell)
         result = inst.prepare()
         self.assertEqual(result, 10)
         self.assertEqual(inst.remain, 10)