fix: add __iter__ and __next__ to FileWrapper for PEP 3333 compliance (#3550)

* fix: add __iter__ and __next__ to FileWrapper for PEP 3333 compliance

The WSGI spec (PEP 3333) requires that wsgi.file_wrapper return an
iterable object. Gunicorn's FileWrapper only implemented __getitem__,
which technically makes it iterable via old-style iteration but breaks
code that explicitly relies on the iterator protocol (e.g., calling
iter() or using next()).

This adds __iter__ (returning self) and __next__ to make FileWrapper
a proper iterator, maintaining backward compatibility with existing
__getitem__-based usage.

Fixes #3396

* Fix lint: move imports to top of file

---------

Co-authored-by: contributor <noreply@users.noreply.github.com>
Co-authored-by: Benoit Chesneau <bchesneau@gmail.com>

gunicorn/http/wsgi.py

@@ -38,6 +38,15 @@ class FileWrapper:
             return data
         raise IndexError
 
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        data = self.filelike.read(self.blksize)
+        if data:
+            return data
+        raise StopIteration
+
 
 class WSGIErrorsWrapper(io.RawIOBase):
 

tests/test_http.py

@@ -9,7 +9,7 @@ from unittest import mock
 
 from gunicorn import util
 from gunicorn.http.body import Body, LengthReader, EOFReader
-from gunicorn.http.wsgi import Response
+from gunicorn.http.wsgi import FileWrapper, Response
 from gunicorn.http.unreader import Unreader, IterUnreader, SocketUnreader
 from gunicorn.http.errors import InvalidHeader, InvalidHeaderName, InvalidHTTPVersion
 from gunicorn.http.message import TOKEN_RE
@@ -253,3 +253,27 @@ def test_eof_reader_read_invalid_size():
 def test_invalid_http_version_error():
     assert str(InvalidHTTPVersion('foo')) == "Invalid HTTP Version: 'foo'"
     assert str(InvalidHTTPVersion((2, 1))) == 'Invalid HTTP Version: (2, 1)'
+
+
+def test_file_wrapper_iterable():
+    """FileWrapper should support the iterator protocol per PEP 3333."""
+    filelike = io.BytesIO(b"hello world")
+    wrapper = FileWrapper(filelike, blksize=5)
+
+    # Should be iterable
+    assert hasattr(wrapper, '__iter__')
+    assert hasattr(wrapper, '__next__')
+    assert iter(wrapper) is wrapper
+
+    # Should yield chunks via next()
+    assert next(wrapper) == b"hello"
+    assert next(wrapper) == b" worl"
+    assert next(wrapper) == b"d"
+    with pytest.raises(StopIteration):
+        next(wrapper)
+
+    # Also works with for loop
+    filelike2 = io.BytesIO(b"abc")
+    wrapper2 = FileWrapper(filelike2, blksize=2)
+    chunks = list(wrapper2)
+    assert chunks == [b"ab", b"c"]