Issue #13781: Fix GzipFile to work with os.fdopen()'d file objects.

Lib/gzip.py

@@ -88,8 +88,12 @@ class GzipFile(io.BufferedIOBase):
         if fileobj is None:
             fileobj = self.myfileobj = __builtin__.open(filename, mode or 'rb')
         if filename is None:
-            if hasattr(fileobj, 'name'): filename = fileobj.name
-            else: filename = ''
+            # Issue #13781: os.fdopen() creates a fileobj with a bogus name
+            # attribute. Avoid saving this in the gzip header's filename field.
+            if hasattr(fileobj, 'name') and fileobj.name != '<fdopen>':
+                filename = fileobj.name
+            else:
+                filename = ''
         if mode is None:
             if hasattr(fileobj, 'mode'): mode = fileobj.mode
             else: mode = 'rb'

Lib/test/test_gzip.py

@@ -274,6 +274,14 @@ class TestGzip(unittest.TestCase):
             d = f.read()
             self.assertEqual(d, data1 * 50, "Incorrect data in file")
 
+    def test_fileobj_from_fdopen(self):
+        # Issue #13781: Creating a GzipFile using a fileobj from os.fdopen()
+        # should not embed the fake filename "<fdopen>" in the output file.
+        fd = os.open(self.filename, os.O_WRONLY | os.O_CREAT)
+        with os.fdopen(fd, "wb") as f:
+            with gzip.GzipFile(fileobj=f, mode="w") as g:
+                self.assertEqual(g.name, "")
+
 def test_main(verbose=None):
     test_support.run_unittest(TestGzip)
 

Misc/NEWS

@@ -89,6 +89,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #13781: Prevent gzip.GzipFile from using the dummy filename provided by
+  file objects opened with os.fdopen().
+
 - Issue #13589: Fix some serialization primitives in the aifc module.
   Patch by Oleg Plakhotnyuk.
 

Modules/posixmodule.c

@@ -6755,6 +6755,8 @@ posix_fdopen(PyObject *self, PyObject *args)
     PyMem_FREE(mode);
     if (fp == NULL)
         return posix_error();
+    /* The dummy filename used here must be kept in sync with the value
+       tested against in gzip.GzipFile.__init__() - see issue #13781. */
     f = PyFile_FromFile(fp, "<fdopen>", orgmode, fclose);
     if (f != NULL)
         PyFile_SetBufSize(f, bufsize);