Add a subprocess test of remapping standard file descriptors (issue #1187).

Lib/test/test_subprocess.py

@@ -955,6 +955,54 @@ def test_close_fds_0_1_2(self):
         # all standard fds closed.
         self.check_close_std_fds([0, 1, 2])
 
+    def test_remapping_std_fds(self):
+        # open up some temporary files
+        temps = [mkstemp() for i in range(3)]
+        try:
+            temp_fds = [fd for fd, fname in temps]
+
+            # unlink the files -- we won't need to reopen them
+            for fd, fname in temps:
+                os.unlink(fname)
+
+            # write some data to what will become stdin, and rewind
+            os.write(temp_fds[1], b"STDIN")
+            os.lseek(temp_fds[1], 0, 0)
+
+            # move the standard file descriptors out of the way
+            saved_fds = [os.dup(fd) for fd in range(3)]
+            try:
+                # duplicate the file objects over the standard fd's
+                for fd, temp_fd in enumerate(temp_fds):
+                    os.dup2(temp_fd, fd)
+
+                # now use those files in the "wrong" order, so that subprocess
+                # has to rearrange them in the child
+                p = subprocess.Popen([sys.executable, "-c",
+                    'import sys; got = sys.stdin.read();'
+                    'sys.stdout.write("got %s"%got); sys.stderr.write("err")'],
+                    stdin=temp_fds[1],
+                    stdout=temp_fds[2],
+                    stderr=temp_fds[0])
+                p.wait()
+            finally:
+                # restore the original fd's underneath sys.stdin, etc.
+                for std, saved in enumerate(saved_fds):
+                    os.dup2(saved, std)
+                    os.close(saved)
+
+            for fd in temp_fds:
+                os.lseek(fd, 0, 0)
+
+            out = os.read(temp_fds[2], 1024)
+            err = support.strip_python_stderr(os.read(temp_fds[0], 1024))
+            self.assertEqual(out, b"got STDIN")
+            self.assertEqual(err, b"err")
+
+        finally:
+            for fd in temp_fds:
+                os.close(fd)
+
     def test_surrogates_error_message(self):
         def prepare():
             raise ValueError("surrogate:\uDCff")