Send *all* output before the BUPMUX header to stderr

This is just an incremental fix.  We may need to follow up with
additional improvements.

Thanks to Johannes Berg for diagnosing the problem.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Tested-by: Rob Browning <rlb@defaultvalue.org>

diff --git a/lib/bup/helpers.py b/lib/bup/helpers.py
index aa691eb69ccd198bfc8560f9f0199c7a6621b970..a6bfeebe2304276f381fa7bae44f097ed9c78506 100644 (file)
--- a/lib/bup/helpers.py
+++ b/lib/bup/helpers.py
@@ -12,7 +12,7 @@ import hashlib, heapq, math, operator, time, grp, tempfile
 
 from bup import _helpers
 from bup import compat
-from bup.compat import argv_bytes, byte_int
+from bup.compat import argv_bytes, byte_int, pending_raise
 from bup.io import byte_stream, path_msg
 # This function should really be in helpers, not in bup.options.  But we
 # want options.py to be standalone so people can include it in other projects.
@@ -561,13 +561,19 @@ class DemuxConn(BaseConn):
         # Anything that comes through before the sync string was not
         # multiplexed and can be assumed to be debug/log before mux init.
         tail = b''
+        stderr = byte_stream(sys.stderr)
         while tail != b'BUPMUX':
+            # Make sure to write all pre-BUPMUX output to stderr
             b = os.read(infd, (len(tail) < 6) and (6-len(tail)) or 1)
             if not b:
-                raise IOError('demux: unexpected EOF during initialization')
+                ex = IOError('demux: unexpected EOF during initialization')
+                with pending_raise(ex):
+                    stderr.write(tail)
+                    stderr.flush()
             tail += b
-            byte_stream(sys.stderr).write(tail[:-6])  # pre-mux log messages
+            stderr.write(tail[:-6])
             tail = tail[-6:]
+        stderr.flush()
         self.infd = infd
         self.reader = None
         self.buf = None