[Bug 48084] New: Consumes 100% CPU when SSH-forwarded connection is refused

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=48084

             Bug #: 48084
           Summary: Consumes 100% CPU when SSH-forwarded connection is
                    refused
    Classification: Unclassified
           Product: Telepathy
           Version: git master
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: idle
        AssignedTo: telepathy-bugs at lists.freedesktop.org
        ReportedBy: will.thompson at collabora.co.uk
         QAContact: telepathy-bugs at lists.freedesktop.org


I run irssi in screen on a remote server, with the irssiproxy plugin listening
on localhost:12345. I then ssh to that server with “LocalForward 12345
localhost:12345”, and tell telepathy-idle to connect to localhost:12345 on my
laptop. (I'll refer to the two differing ideas of “localhost” as “laptop” and
“vm” to avoid confusion.)

If the irssiproxy plugin isn't loaded, then Idle eats my CPU and never finishes
connecting. Here's what seems to happen:

• Idle establishes a connection to laptop:12345.
• The ssh client accepts the connection, and forwards it.
• ssh on the vm tries to connect to vm:12345, which fails because nothing is
listening (“channel 4: open failed: connect failed: Connection refused”, says
SSH).
• Meanwhile, Idle transport is established:



** (telepathy-idle:27876): DEBUG: change_state: emitting status-changed, state
2, reason 1
** (telepathy-idle:27876): DEBUG: sconn_status_changed_cb: called with state 2

[Thread 0x7ffff381d700 (LWP 27886) exited]
** (telepathy-idle:27876): DEBUG: msg_queue_timeout_cb: called
** (telepathy-idle:27876): DEBUG: idle_server_connection_send_async: sending
"PASS topsecr3t
" to OutputStream 0x656c00
** (telepathy-idle:27876): DEBUG: msg_queue_timeout_cb: called
** (telepathy-idle:27876): DEBUG: idle_server_connection_send_async: sending
"NICK wjt
" to OutputStream 0x656c00
** (telepathy-idle:27876): DEBUG: _write_ready: g_output_stream_write failed :
Error sending data: Broken pipe
** (telepathy-idle:27876): DEBUG: _msg_queue_timeout_ready:
idle_server_connection_send failed: Error sending data: Broken pipe
** (telepathy-idle:27876): DEBUG: msg_queue_timeout_cb: called
** (telepathy-idle:27876): DEBUG: idle_server_connection_send_async: sending
"NICK wjt
" to OutputStream 0x656c00
** (telepathy-idle:27876): DEBUG: _write_ready: g_output_stream_write failed :
Error sending data: Broken pipe
** (telepathy-idle:27876): DEBUG: _msg_queue_timeout_ready:
idle_server_connection_send failed: Error sending data: Broken pipe

and so on, ad infinitum.

So the issue seems to be that IdleServerConnection does not blow itself up if
g_output_stream_write_finish() fails, and nor does IdleConnection. The latter
restores the unsent message to the queue to try again later.

The 100% CPU usage is caused by g_input_stream_read_finish() returning 0—which,
per the documentation for g_input_stream_read_async(), means EOF:

> On success, the number of bytes read into the buffer will be passed
> to the callback. It is not an error if this is not the same as the
> requested size, as it can happen e.g. near the end of a file, but
> generally we try to read as many bytes as requested. Zero is returned
> on end of file (or if count is zero), but never otherwise.

So here are a few things which could/should be done:

• IdleServerConnection should blow itself up if a write fails (or
IdleConnection could do that);
• IdleConnection should not try to requeue failed messages—it should just end
the connection, one way or another.
• IdleServerConnection should end the connection if
g_input_stream_read_finish() returns 0.

Let's see…

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