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borg serve: fix transmission data loss of pipe writes, fixes #1268

This problem was found on cygwin/windows due to its small pipe buffer size of 64kiB.

Due to that, bigger (like >64kiB) writes are always only partially done and os.write() returns
the amount of data that was actually sent. the code previously did not use that return value
and assumed that always all is sent, which led to a loss of the remainder of transmission data
and usually some "unexpected RPC data format" error on the client side.

Neither Linux nor *BSD ever do partial writes on blocking pipes, unless interrupted by a
signal, in which case serve() would terminate.
This commit is contained in:
Thomas Waldmann 2017-01-13 19:09:57 +01:00
parent 9c42a75831
commit 941b8d7778

View file

@ -7,6 +7,7 @@
import sys
import tempfile
import textwrap
import time
from subprocess import Popen, PIPE
from . import __version__
@ -28,6 +29,23 @@
MAX_INFLIGHT = 100
def os_write(fd, data):
"""os.write wrapper so we do not lose data for partial writes."""
# This is happening frequently on cygwin due to its small pipe buffer size of only 64kiB
# and also due to its different blocking pipe behaviour compared to Linux/*BSD.
# Neither Linux nor *BSD ever do partial writes on blocking pipes, unless interrupted by a
# signal, in which case serve() would terminate.
amount = remaining = len(data)
while remaining:
count = os.write(fd, data)
remaining -= count
if not remaining:
break
data = data[count:]
time.sleep(count * 1e-09)
return amount
class ConnectionClosed(Error):
"""Connection closed by remote host"""
@ -106,7 +124,7 @@ def serve(self):
if self.repository is not None:
self.repository.close()
else:
os.write(stderr_fd, "Borg {}: Got connection close before repository was opened.\n"
os_write(stderr_fd, "Borg {}: Got connection close before repository was opened.\n"
.format(__version__).encode())
return
unpacker.feed(data)
@ -133,9 +151,9 @@ def serve(self):
logging.exception('Borg %s: exception in RPC call:', __version__)
logging.error(sysinfo())
exc = "Remote Exception (see remote log for the traceback)"
os.write(stdout_fd, msgpack.packb((1, msgid, e.__class__.__name__, exc)))
os_write(stdout_fd, msgpack.packb((1, msgid, e.__class__.__name__, exc)))
else:
os.write(stdout_fd, msgpack.packb((1, msgid, None, res)))
os_write(stdout_fd, msgpack.packb((1, msgid, None, res)))
if es:
self.repository.close()
return