Fix sporadic "Resource temporarily unavailable" error

Issue reported on the mailing list while backing up to a remote
repository on OS X over a slow uplink.

CHANGES

@@ -8,6 +8,7 @@ Version 0.13
 
 (feature release, released on X)
 
+- Fix sporadic "Resource temporarily unavailable" when using remote repositories
 - Reduce file cache memory usage (#90)
 - Faster AES encryption (utilizing AES-NI when available)
 - Experimental Linux, OS X and FreeBSD ACL support (#66)

attic/remote.py

@@ -1,3 +1,4 @@
+import errno
 import fcntl
 import msgpack
 import os
@@ -195,7 +196,13 @@ def fetch_from_cache(args):
                         self.to_send = msgpack.packb((1, self.msgid, cmd, args))
 
                 if self.to_send:
-                    self.to_send = self.to_send[os.write(self.stdin_fd, self.to_send):]
+                    try:
+                        self.to_send = self.to_send[os.write(self.stdin_fd, self.to_send):]
+                    except OSError as e:
+                        # io.write might raise EAGAIN even though select indicates
+                        # that the fd should be writable
+                        if e.errno != errno.EAGAIN:
+                            raise
                 if not self.to_send and not (calls or self.preload_ids):
                     w_fds = []
         self.ignore_responses |= set(waiting_for)