Added port forwarder example.

doc/examples.rst

@@ -54,4 +54,10 @@ Feed Scraper
 
 This example requires `Feedparser <http://www.feedparser.org/>`_ to be installed or on the PYTHONPATH.
 
-.. literalinclude:: ../examples/feedscraper.py
+.. literalinclude:: ../examples/feedscraper.py
+
+Port Forwarder
+-----------------------
+``examples/forwarder.py``
+
+.. literalinclude:: ../examples/forwarder.py

examples/forwarder.py

@@ -0,0 +1,24 @@
+""" This is an incredibly simple port forwarder from port 7000 to 22 on localhost.  It calls a callback function when the socket is closed, to demonstrate one way that you could start to do interesting things by
+starting from a simple framework like this.
+"""
+
+import eventlet
+def closed_callback():
+    print "called back"
+
+def forward(source, dest, cb = lambda: None):
+    """Forwards bytes unidirectionally from source to dest"""
+    while True:
+        d = source.recv(32384)
+        if d == '':
+            cb()
+            break
+        dest.sendall(d)
+
+listener = eventlet.listen(('localhost', 7000))
+while True:
+    client, addr = listener.accept()
+    server = eventlet.connect(('localhost', 22))
+    # two unidirectional forwarders make a bidirectional one
+    eventlet.spawn_n(forward, client, server, closed_callback)
+    eventlet.spawn_n(forward, server, client)