Bug 2108

Created attachment 2275 [details]
update sftp upload progress only when acks are received

http://bugs.debian.org/708372 reports that the scp progress meter updates to 100% before the file has been fully transferred.  I looked at whether it's possible to fix this within the constraints of the existing scp "protocol" (such as it is), and I think it probably isn't; the scp client would have to know that it's expecting the scp target to send back acknowledgement messages, which is going to be pretty difficult to arrange.  So my first impulse was to reply to say that this isn't possible in scp, but that the reporter should use sftp instead, and perhaps some day we'll make the scp client actually use the SFTP protocol under the covers (as is done by e.g. PuTTY's pscp).  However, I then went to check that sftp behaves sensibly, and it has the exact same bug.  Oops.

Fortunately, I think this is easy to fix.  The sftp client already keeps a list of the acknowledgements it's waiting for so that it can block in a loop until they've all arrived, and those acknowledgements already record the length of each chunk of data.  So all we need to do is update the progress counter when acks come back rather than when we send the data, taking care to separate the progress counter from the offset of the next chunk of data to send.  How does this patch look?