Merge pull request #2032 from ThomasWaldmann/fix-pipe-write

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

borg/remote.py

@@ -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