Issue

This appeared on MAC-OS X with tcl8.6.1.

Demo

% proc accept {s a p} {
     puts ok
}
% socket -server accept -myaddr 127.0.0.1 61680
sock192
% vwait a

In a second tclsh, the following is run:

% set client [socket -async localhost 61680]
sock103825910
% fconfigure $client -error
connection refused
% update
% fconfigure $client -error
% fconfigure $client -sockname
::1 localhost 64153

The issue is the flagged "connection refused" and the final connect.

References

Reported by DKF on Ticket [13d3af3ad5] and copied here by oehhar.

Just for completeness: the tracing I mentioned in the last comment doesn't work as I thought, because [fconfigure -peername] is not available before the socket is connected.

Fixed in [80ca9fe746] and [f644fb5a9f].

When implementing multi-address [socket -async], I thought it would only be used together with fileevent, and [fconfigure -error] would not be called before the readable event has fired. But now I see that -async without fileevent even makes sense, e.g. to trace the addresses that were tried and why each of them failed, so the error caching (reading SO_ERROR is destructive) needs to go both ways, from the event handler hidden behind [socket -async] to [fconfigure -error] and vice versa.

To be clear, the issue is that looking at the transient error prevents the client from ever connecting. That's much more serious than merely seeing a transient error.