1 files changed, 35 insertions, 0 deletions
diff --git a/doc/core/howto/listings/sendmsg/copy_descriptor.py b/doc/core/howto/listings/sendmsg/copy_descriptor.py
new file mode 100644
index 0000000..1c9a774
--- /dev/null
+++ b/doc/core/howto/listings/sendmsg/copy_descriptor.py
@@ -0,0 +1,35 @@
+# Copyright (c) Twisted Matrix Laboratories.
+# See LICENSE for details.
+
+"""
+Demonstration of copying a file descriptor over an AF_UNIX connection using
+sendmsg.
+"""
+
+from os import pipe, read, write
+from socket import SOL_SOCKET, socketpair
+from struct import unpack, pack
+
+from twisted.python.sendmsg import SCM_RIGHTS, send1msg, recv1msg
+
+def main():
+    foo, bar = socketpair()
+    reader, writer = pipe()
+
+    # Send a copy of the descriptor.  Notice that there must be at least one
+    # byte of normal data passed in.
+    sent = send1msg(
+        foo.fileno(), "\x00", 0,
+        [(SOL_SOCKET, SCM_RIGHTS, pack("i", reader))])
+
+    # Receive the copy, including that one byte of normal data.
+    data, flags, ancillary = recv1msg(bar.fileno(), 1024)
+    duplicate = unpack("i", ancillary[0][2])[0]
+
+    # Demonstrate that the copy works just like the original
+    write(writer, "Hello, world")
+    print "Read from original (%d): %r" % (reader, read(reader, 6))
+    print "Read from duplicate (%d): %r" % (duplicate, read(duplicate, 6))
+
+if __name__ == '__main__':
+    main()