Bugs item #3048197, was opened at 2010-08-19 00:59
Message generated for change (Comment added) made by bagder
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Category: ftp
Group: bad behaviour
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: catalin (catalinr)
Assigned to: Daniel Stenberg (bagder)
Summary: Incorrect data uploaded in case of CURLE_SEND_ERROR

Initial Comment:
These are my [hopefully right] conclusions:
- When doing an FTP upload, in the progressCallback function the uploadedTillNow argument (last one) holds the correct size for the uploaded data (well, rather "sent data");
- the uploaded data is sent in chunks of at most CURL_MAX_WRITE_SIZE bytes (btw, CURL_MAX_WRITE_SIZE is not documented anywhere and it'd be useful to know that that is the maximum size attempted to be uploaded at one time);
- in case the link is broken/disconnected, the remote destination file gets appended with a chunk of the size reported by progressCallback but the last KB are composed of NULL bits and not the real data. So a subsequent APPE[-nd] to that file will render a file of the same size with the original one, but somewhere in the middle it'll have the wrong NULL bytes.

The workaround for this was to add the size reported by the progressCallback in a totalTillNow variable, and after any network error that would require a resume subtract CURL_MAX_WRITE_SIZE*8 from totalTillNow, and setup a REST upload with the calculated starting point. (See #3048174 for issues with CURLOPT_RESUME_FROM).

I'm not sure if my workaround is the best solution, but it works. OTOH, that behavior when uploading and getting disconnected leads to corrupted files at destination and that is IMO very wrong...

libcurl 7.21.1
msw Vista
mingw-gcc 3.4.5

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>Comment By: Daniel Stenberg (bagder)
Date: 2010-08-19 15:15

Message:
I don't see how libcurl sends any data as zeroes. Also, I fail to see how
it could send that block of zeroes if the connection disconnected?

To me it sounds like your server behaves oddly and add random data to the
file being written at the time of the disconnect. I don't think libcurl can
do anything about it.

If this is not the case, can you please clarify your point for us?

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Received on 2010-08-19