We're running version 0.10 of Net::SFTP and version 1.29 of Net::SSH::Perl. The server we're connecting to is a "5.0.1.79 SSH Tectia Server", with protocol version 2.0.

When small files are transferred Net::SFTP works perfectly. When they get larger than a few kilobytes they hang at this point:

sftp: Sending SSH2_FXP_INIT
sftp: Remote version: 3
sftp: Sent SSH2_FXP_OPEN I:0 P: "filename"
sftp: Sent message T:17 I:1
sftp: Received stat reply T:105 I:1
sftp: Sent message SSH2_FXP_WRITE I:2 O:0

That's in the "do_write" procedure. So we've been trying different things to figure out what's wrong, and one thing that worked is to change the value of COPY_SIZE in SFTP.pm from 8192 to something lower (4063 and lower seem to make it work).

Does anyone have an idea why this is happening and why changing COPY_SIZE fixed it? Below is the test script we're using:

We dug a little deeper and the hang seems to be in the SSH library, not SFTP. It occurs when the amount of data sent exceeds the packet size defined by the remote server (it was roughly 4kb for Tectia). This triggers some buffering in the Perl SSH library. Changing the COPY_SIZE means you're basically doing the buffering yourself. Maybe some sample cases will make it clearer:

* COPY_SIZE=8kb, file size=3kb:
  3kb string put with Net::SFTP
  Net::SFTP examines COPY_SIZE: 8kb
  Net::SFTP sends 3kb to Net::SSH
  Net::SSH examines Tectia packet size: 4kb
  Net::SSH sends 3kb
  *success*

* COPY_SIZE=8kb, file size=10kb:
  10kb string put with Net::SFTP
  Net::SFTP examines COPY_SIZE: 8kb
  Net::SFTP sends first 8kb of 10kb to Net::SSH
  Net::SSH examines Tectia packet size: 4kb
  Net::SSH buffering triggered
  Net::SSH sends first 4kb of 8kb
  *Net::SSH hangs waiting for Tectia response*

* COPY_SIZE=4kb, file size=3kb
  ...same as first
  *success*

* COPY_SIZE=4kb, file size=10kb
  10kb string put with Net::SFTP
  Net::SFTP examines COPY_SIZE: 4kb
  Net::SFTP sends first 4kb of 10kb to Net::SSH
  Net::SSH examines Tectia packet size: 4kb
  Net::SSH sends 4kb
  Net::SFTP sends next 4kb of 10kb to Net::SSH
  Net::SSH examines Tectia packet size: 4kb
  Net::SSH sends 4kb
  Net::SFTP sends final 2kb of 10kb to Net::SSH
  Net::SSH examines Tectia packet size: 4kb
  Net::SSH sends 2kb
  *success*

It appears there's an issue with the interaction between Perl SSH and Tectia 5.0.x when multiple data packets need to be sent. We've only encountered this problem when using this specific SFTP/SSH library and this specific Tectia server (4.0.x seems fine), so we don't know what's up. We'll probably end up using Net::SFTP::Foreign.

I am experiencing a very similar thing. I have net::SFTP installed on a solaris 8 server, connecting to a linux server. The upload starts and I get the error below on the second packet. The file size is exactly the total size of those 2 numbers in the SSH2_FXP_WRITE statements (8192 + 5821). This is my ftp variable that is used through-out the script. Where do you change the COPY_SIZE parameter? Any ideas or suggestions would help. Just a note: I am using Net::xFTP to be able to use the ftp variables in the sftp module.

server: sftp: Sent message T:16 I:9 server: sftp: Sent message T:16 I:10 server: sftp: Sent message T:16 I:11 server: sftp: Sent SSH2_FXP_OPEN I:12 P:/opt/websites/ register.company.org/hccs/WC_file.dat server: sftp: Sent message SSH2_FXP_WRITE I:13 O:0 server: sftp: In write loop, got 8192 offset 0 server: sftp: Sent message SSH2_FXP_WRITE I:14 O:8192 server: sftp: In write loop, got 5821 offset 8192 server: sftp: Sent message T:10 I:15 Uploading WC_file.dat to Server .......... Error: ./ uploadSSH_company2.pl could not upload WC_file.dat to Server.