SFTP in R11B

Serge Aleynikov <>
Wed Jun 14 19:43:15 CEST 2006

I've been experimenting with the SSH application in R11B, and found that 
in some occasions when an ssh_sftp client cannot establish connection 
with an SFTP server, the ssh_sftp client crashes misarably producing a 
nice chunk of CRASH REPORTs when SASL is started.

A dive into the ssh_sftp's source led to the following observations:

1. SFTP clients starts an connection manager ssh_cm.  The later is 
implemented as a gen_server process that doesn't carefully handle 
exceptions in user_auth call leading to a leaky exception in the 
gen_server's init/1.  That is easy to fix:

--- lib/ssh/src/ssh_cm.erl      2006-06-07 18:24:43.767831191 -0400
+++ lib/ssh/src/ssh_cm.erl      2006-06-07 18:45:01.594608966 -0400
@@ -199,7 +199,7 @@
  init([client, User, Host, Port, Opts]) ->
      case ssh_transport:connect(Host, Port, Opts) of
         {ok, SSH} ->
-           case user_auth(SSH, Opts) of
+           case catch user_auth(SSH, Opts) of
                 ok ->
                     SSH ! {ssh_install, connect_messages()},
                     process_flag(trap_exit, true),

2. However, in this case gen_server's init/1 returns {stop, Reason}. 
This is an expected callback's return value, but because the Reason is 
not normal, this still produces a sasl CRASH REPORT.  I am not sure this 
is a good thing.  I'd like to be able to do:

ssh_sftp:connect(Host, Opts) -> {ok, Pid} | {error, Reason}

without getting a crash report.  Is there a way to avoid that?

Additionally, here's a reference to another ssh_sftp patch fixing sftp's 
hanging issue:




Serge Aleynikov
R&D Telecom, IDT Corp.
Tel: (973) 438-3436
Fax: (973) 438-1464

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