[JSch-users] Sftp Hangs for large files - the fix

[Lindani Phiri <lphiri@nc...>]

I found that sending (put)  any files larger than 1K were hanging the 
jsch client.
The problem in my case was that my server had stringent  window size 
requirements  (max  1K).
The client was then hanging in the write  method of  Session.java:


public /*synchronized*/ void write(Packet packet, Channel c, int length) 
throws Exception{
 
    while(true){
      if(c.rwsize>length){
        c.rwsize-=length;
        break;
      }
      try{
       Thread.sleep(10);
     
      }catch(Exception e){};
    }
    write(packet);
  }
 

In my case c.rwsize>length  will never be true for files larger than 1K 
(put method attempts to read in 1024 bytes at a time)  , so I got stuck 
in the while loop.

My fix for this was to check for the available remote window size 
(rwsize)  in  the put method of  ChannelSftp and make sure that I only 
attempt
to send  a length smaller then the available window space (minus any 
packet padding  such as handle.length) . This also improved my 
performance as I can send much more than the hardcoded 1024 bytes at a 
time, if the window space is available.
Also I changed the above code to :

public /*synchronized*/ void write(Packet packet, Channel c, int length) 
throws Exception{
    int retry = 0;
    while(true){
      if(c.rwsize>length){
        c.rwsize-=length;
        break;
      }
     
       Thread.sleep(10);
       retry++;
        if  (retry > 10000) throw Exception("Unable to negotiate 
adequate window size"); //wait for only 100s
    }
    write(packet);
  }

So the caller can at least get an exception if the required window size 
is not obtained in after a certain wait.

LD.

Re: [JSch-users] Sftp Hangs for large files - the fix

[<ymnk@jc...>]

Hi,

Thank you for feedback.

   +-From: Lindani Phiri <lphiri@...> --
   |_Date: Fri, 27 Feb 2004 10:47:26 -0500 ___
   |
   |I found that sending (put) any files larger than 1K were hanging
   |the jsch client.  The problem in my case was that my server had
   |stringent window size requirements (max 1K).  The client was then
   |hanging in the write method of Session.java:

Do you mean that ....

  $ ssh -v -v localhost
  Connecting to localhost...
  OpenSSH_3.4p1, SSH protocols 1.5/2.0, OpenSSL 0x0090701f
  debug1: Reading configuration data /home/yamanaka/.ssh/config
  ... snip ...
  debug1: Sending subsystem: sftp
  debug1: channel request 0: subsystem
  debug2: callback done
  debug1: channel 0: open confirm rwindow 0 rmax 32768
  debug2: channel 0: rcvd adjust 131072          <---------------- 
  debug2: Remote version: 3
  sftp> 

131072 has been 1024 on your environment? 

Anyway, I have understood what is the problem and 
I will post the revised version to fix this problem within a few days.  
# I'm sorry, but I'm a little bit busy now. 


Thanks,
--
ymnk

Re: [JSch-users] Sftp Hangs for large files - the fix

[<ymnk@jc...>]

Hi,

   +-From: Lindani Phiri <lphiri@...> --
   |_Date: Fri, 27 Feb 2004 10:47:26 -0500 ___
   |
   |I found that sending (put) any files larger than 1K were hanging
   |the jsch client.  The problem in my case was that my server had
   |stringent window size requirements (max 1K).

I could reproduce your problem by reducing the window size of sshd.
But, I had to re-compile it from the source code.  I'm very interested in
your sshd.  Why your sshd has such a small window size?
Do you know the reason?

Anyway, please try
  http://www.jcraft.com/jsch/jsch-0.1.14-rc1.zip
It is just a quick hack, but I have confirmed that it will work for
such a sshd.

Thanks,
--
ymnk

RE: [JSch-users] Sftp Hangs for large files - the fix

[Filip Hanik \(lists\) <devlists@ha...>]

this is the same place the scp with Ant was hanging.

Filip

-----Original Message-----
From: jsch-users-admin@...
[mailto:jsch-users-admin@...]On Behalf Of Lindani
Phiri
Sent: Friday, February 27, 2004 7:47 AM
To: jsch-users@...
Subject: [JSch-users] Sftp Hangs for large files - the fix


I found that sending (put)  any files larger than 1K were hanging the 
jsch client.
The problem in my case was that my server had stringent  window size 
requirements  (max  1K).
The client was then hanging in the write  method of  Session.java:


public /*synchronized*/ void write(Packet packet, Channel c, int length) 
throws Exception{
 
    while(true){
      if(c.rwsize>length){
        c.rwsize-=length;
        break;
      }
      try{
       Thread.sleep(10);
     
      }catch(Exception e){};
    }
    write(packet);
  }
 

In my case c.rwsize>length  will never be true for files larger than 1K 
(put method attempts to read in 1024 bytes at a time)  , so I got stuck 
in the while loop.

My fix for this was to check for the available remote window size 
(rwsize)  in  the put method of  ChannelSftp and make sure that I only 
attempt
to send  a length smaller then the available window space (minus any 
packet padding  such as handle.length) . This also improved my 
performance as I can send much more than the hardcoded 1024 bytes at a 
time, if the window space is available.
Also I changed the above code to :

public /*synchronized*/ void write(Packet packet, Channel c, int length) 
throws Exception{
    int retry = 0;
    while(true){
      if(c.rwsize>length){
        c.rwsize-=length;
        break;
      }
     
       Thread.sleep(10);
       retry++;
        if  (retry > 10000) throw Exception("Unable to negotiate 
adequate window size"); //wait for only 100s
    }
    write(packet);
  }

So the caller can at least get an exception if the required window size 
is not obtained in after a certain wait.

LD.



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Re: [JSch-users] Sftp Hangs for large files - the fix

[<ymnk@jc...>]

Hi,

   +-From: "Filip Hanik (lists)" <devlists@...> --
   |_Date: Tue, 2 Mar 2004 08:52:26 -0800 __
   |
   |this is the same place the scp with Ant was hanging.

May I ask you to try
  http://www.jcraft.com/jsch/jsch-0.1.14-rc1.zip

Thanks,
--
ymnk