Use poll implementation to fix file descriptor leak

fabric/context_managers.py

@@ -455,19 +455,30 @@ def shell_env(**kw):
 
 
 def _forwarder(chan, sock):
-    # Bidirectionally forward data between a socket and a Paramiko channel.
-    while True:
-        r, w, x = select.select([sock, chan], [], [])
-        if sock in r:
-            data = sock.recv(1024)
-            if len(data) == 0:
-                break
-            chan.send(data)
-        if chan in r:
-            data = chan.recv(1024)
-            if len(data) == 0:
-                break
-            sock.send(data)
+    """
+    Bidirectionally forward data between a socket and a Paramiko channel.
+    """
+    mapping = {
+        sock.fileno(): (sock, chan),
+        chan.fileno(): (chan, sock),
+    }
+    poller = select.poll()
+    for fd in mapping:
+        poller.register(fd, select.POLLIN)
+    active = True
+    while active:
+        events = poller.poll()
+        for fd, flag in events:
+            if flag & select.POLLIN:
+                sender, receiver = mapping[fd]
+                data = sender.recv(1024)
+                if data:
+                    receiver.send(data)
+                else:
+                    active = False
+            # Handle unexpected hangups
+            if flag & select.POLLHUP:
+                active = False
     chan.close()
     sock.close()
 

fabric/io.py

@@ -2,7 +2,7 @@
 import sys
 import socket
 import time
-from select import select
+import select
 from collections import deque
 
 import six
@@ -268,8 +268,9 @@ def input_loop(chan, f, using_pty):
             if msvcrt.kbhit():
                 byte = msvcrt.getch()
         elif waitable:
-            r, w, x = select([f], [], [], 0.0)
-            if f in r:
+            poller = select.poll()
+            poller.register(f, select.POLLIN)
+            if poller.poll(0):
                 byte = f.read(1)
         else:
             byte = f.read(1)