Mr. Lamaison, I apologize for not replying sooner. Gmail hid your reply for some reason, and I did not notice it until just now.
On 3/29/12, Alexander Lamaison <sw...@lammy.co.uk> wrote: > On 29 March 2012 01:19, Adam Craig <adamgcr...@accessnoexcuse.org> wrote: >> Hello Libssh2 Dev Mailing List, >> >> I am working on a cocoa application that uses libssh2 to SFTP files to >> and from a server. > > ... snip > >> I have been testing this method with both small text files of a few kB >> each and Quicktime .mov files of up to 1MB. I am running the app on >> 64-bit Intel OS X 10.6.8 on the client side and communicating with a >> server running the standard linux sftp-server on Redhat Enterprise >> Linux Server 5.6. The version of libssh2 I am using is 1.4.0-20120229. >> >> For all files I have tested, the method downloads and returns the >> correct data, but it always returns it in chunks no larger than 2K, >> regardless of how large I make the buffer and regardless of the size >> of the file. More precisely, if the file is smaller than 2K, the first >> call downloads the complete file and returns the number of bytes in >> the file, but, if the file is larger than 2K, libssh2_sftp_read >> returns a value of 2000 after every call except for the second-to-last >> call, which returns (file size)%2000, and the last call, which returns >> 0, indicating we have read all the bytes in the file. At first, I >> thought it might be a peculiarity of the server's configuration, but I >> do not see any hard limit on sent packet size in sftp-server's >> documentation. Is this an inherent limitation of the libssh2_sftp_read >> method? > > So just to summarise, you're not reporting that the transfer is > incomplete? Just that you wish the transfer used bigger chunks at a > time? This is a perfectly valid thing to report, I just want to check > I'm understanding you correctly. > That is correct. > ... snip > >> I am testing this with the same client macbook and server and the same >> version of libssh2. If I upload a file smaller than 30K, >> libssh2_sftp_write, the program tries to upload it all in one call, >> succeeds, and returns the correct number of bytes. If I upload a file >> larger than 30K but smaller than packet_size, it attempts to upload >> all the data in one call. The complete file appears on the server, but >> libssh2_sftp_write only returns 30000. If I upload a file larger than >> the packet size, each full-packet call returns 30000, causing the loop >> to slide the window forward by 30000. Once it gets to a point where >> fewer than packet_size bytes remains, it jumps to the last call and >> tries to upload all the remaining bytes. This call returns up to >> 30000. When I check the server, it has the complete file. >> It appears that the return value and the amount of data uploaded do not >> match. > > This sounds like the expected behaviour of libssh2's pipelined SFTP > architecture. The return value doesn't have to correspond to the > amount uploaded on _that_ call as long as the overall total is > correct. The last call that doesn't appear to do anything allows > libssh2 to do some housekeeping. What do you mean by the "overall total?" If I upload a file of 200K all in one call to libssh2_sftp_write and it returns 30K when it actually uploaded all 200K, what does the 30K return value mean? Does the documentation explain this somewhere? All te information on this I could find was http://www.libssh2.org/libssh2_sftp_write.html: "RETURN VALUE Actual number of bytes written or negative on failure. If used in non-blocking mode, it returns LIBSSH2_ERROR_EAGAIN when it would otherwise block. While LIBSSH2_ERROR_EAGAIN is a negative number, it isn't really a failure per se. If this function returns 0 (zero) it should not be considered an error, but simply that there was no error but yet no payload data got sent to the other end." > >> I would like to be able to download larger packets > > I'm not sure why yours are limited to 2K but I believe this is > negotiated with the server (jump in here guys if I'm wrong) so it's > possible your server is refusing to send bigger packets. That was my first guess, and it may be the case. After looking at the documentation for the server-side SFTP tool and not finding any information about a maximum packet size, I decided to look into whether it was an issue with Libssh2. Documentation I read for the SFTP server utility to which the app is connecting: http://www.openbsd.org/cgi-bin/man.cgi?query=sftp-server&sektion=8 http://www.openbsd.org/cgi-bin/man.cgi?query=sshd_config&sektion=5 Adam > > Alex > > -- > Swish - Easy SFTP for Windows Explorer (http://www.swish-sftp.org) > _______________________________________________ > libssh2-devel http://cool.haxx.se/cgi-bin/mailman/listinfo/libssh2-devel > _______________________________________________ libssh2-devel http://cool.haxx.se/cgi-bin/mailman/listinfo/libssh2-devel
