Re: [JSch-users] SFTP slow file transfer speed with Titan FTP

[Thomas K. <tho...@ou...>]

I've managed to overcome this issue myself. First, I tried to find out where the blocking actually occurs. After a number of sent bulk requests the ChannelSftp.header(Buffer, Header) method gets blocked for exactly 60 seconds, that's the stack trace:

    Daemon Thread [Camel (camel-1) thread #0 - sftp://secret/archive] (Suspended)	
	waiting for: Channel$MyPipedInputStream  (id=26)	
	Object.wait(long) line: not available [native method]	
	Channel$MyPipedInputStream(PipedInputStream).read() line: 326	
	Channel$MyPipedInputStream(PipedInputStream).read(byte[], int, int) line: 377	
	ChannelSftp.fill(byte[], int, int) line: 2605	
	ChannelSftp.header(Buffer, ChannelSftp$Header) line: 2631	
	ChannelSftp.access$11(ChannelSftp, Buffer, ChannelSftp$Header) line: 2629	
	ChannelSftp$2.read(byte[], int, int) line: 1282	
	ChannelSftp$2.read(byte[]) line: 1232	
	FileOperations.writeFileByStream(InputStream, File) line: 382	

I don't know what is causing this. After the "timeout" occurred processing continued until the next outage. I tried to reproduce the "bug" with Openssh's sftp command and the -R (num_requests) argument which I think is meant by "sending multiple requests at any one time". As Openssh's sftp works well I compared the ChannelSftp implementation with what is in sftp-client.c. The only obvious difference I found is the "rq.count()==0" condition in "ChannelSftp.get(String, SftpProgressMonitor, long).new InputStream() {...}.read(byte[], int, int)". Removing the condition fixes the issue for me.

Can this be considered as a bug? Is this something eligible for a next version of JSCH?

The following patch is based upon jsch-0.1.53:

--- src/com/jcraft/jsch/ChannelSftp.java
+++ src/com/jcraft/jsch/ChannelSftp.java
@@ -1374,17 +1374,16 @@
                len=1024; 
              }
 
-             if(rq.count()==0) {
-               int request_len = buf.buffer.length-13;
-               if(server_version==0){ request_len=1024; }
 
-               while(rq.count() < request_max){
-                 try{
-                   sendREAD(handle, request_offset, request_len, rq);
-                 }
-                 catch(Exception e){ throw new IOException("error"); }
-                 request_offset += request_len;
+             int request_len = buf.buffer.length-13;
+             if(server_version==0){ request_len=1024; }
+
+             while(rq.count() < request_max){
+               try{
+                 sendREAD(handle, request_offset, request_len, rq);
                }
+               catch(Exception e){ throw new IOException("error"); }
+               request_offset += request_len;
              }
 
              header=header(buf, header);

Thanks for considering this.

Regards,
Thomas