Version 18 of socket -async

Purpose

This page is dedicated to the asyncroneous socket connect, started by 'socket -async'. See the socket page for a general description.

It also serves as communication page for development and compares current TCL 8.5.15, TCL 8.6.1 and future versions.

Async connect got more complicated in TCL 8.6, as multiple destination IPs are internally supported (due to IPV6 or DNS lookup resulting in multiple IPs).

Command behaviour

socket -async

'socket -async' host first does a syncroneous DNS lookup.

Then the connect is started as background process.

• In TCL8.5, this terminates without any interaction by background processes.
• In TCL8.6, the event loop or command invocation is required to check multiple IPs.

update,vwait

Starting the event loop allows in TCL8.6 to continue with the next try or to fail finally

fileevent writable

Fires when async connect terminates with success or error.

fileevent readable

Fires when async connect terminates with error.

blocking gets,read,puts

The async connect is terminated syncroneously.

On success, the operation is performed.

On connect failure, the connect error is returned by the command. (still to discuss)

non blocking gets,read,puts

The async connect state is checked or continued (next IP) in a non-blocking way.

Possible results:

Implementation status:

close

A close while connection is in progress or after a succesful connection should succeed.

A close after a failed connection should return the connect error if not jet reported.

fconfigure

Any fconfigure command on the socket continues the connect process.

fconfigure -error

A final connect error should be returned by 'fconfigure -error'. No error should be flagged while connection is running.

Implementation status:

fconfigure -sockname

My own IP of the socket connection. Returns list of IP, Name, Port.

Since IPV6, this value may change within connect tries from "127.0.0.1" to "::1". Also the port may change.

Implementation status:

Idea: The connection process should not be reflected. A compatibility value or an error should returned while connecting.

If we reflect the connection process, we would have issues later, if we would push the connect process to an own thread.

fconfigure -peername

The destination IP. Returns list of IP, Name, Port.

Since IPV6, this value may change within connect tries. Also the port may change (if auto).

Implementation status:

Idea: The connection process should not be reflected. A compatibility value or an error should returned while connecting.

TIPs

Behaviour of fconfigure -peername, -sockname, -error, -connecting

A discussion tip on the behaviour of those commands while connecting was drafted.

A new option '-connecting' should return 1 if connection is still in process.

Reason for that: there are use cases for socket -async without event loop.

Example: Within Web-Server verify multiple servers for connectivity. Open many sockets in the background, do some other calculations, check if connect terminated by "-connecting".

fconfigure -errorno

A possibility to return the full POSIX information of a background error was drafted.

Two possible solutions:

• fconfigure -errordict: returns a dict as 'catch {} e d'
• fconfigure -invokeerror: throws the stored background error or does nothing if no error present

Bugs

Win TCL8.6.1 only tries first IP

Bug 13d3af3ad5

TCL8.6.1 only tries the first of eventual multiple IP addresses to connect. This may cause serious connect issues with IPV6.

This is fixed in branch bug-13d3af3ad5 which also serves as main branch to fix all bugs in TCL8.6.1 and to test enhancements too.

Win connect ignored

Bug 336441ed59

When a connect terminates to quick so the notifier is not ready yet, the connect is ignored and thus it waits forever for it.

Test is timing dependent and may ignore issue on some machines.

Empty error message on close on failed background flush

Bug 97069ea11a

set h [open dummy]
fconfigure $h -seterror EWOULDBLOCK
fileevent $h writable {set x writable}
fconfigure $h -blocking 0
puts $h abc
fconfigure $h -setwritable 1
vwait x
catch {close $h} e d

==== socket-14.7.2 pending [socket -async] and blocking [gets], no listener FAILED
==== Contents of test case:

        set sock [socket -async localhost [randport]]
        catch {gets $sock} x
        list $x [fconfigure $sock -error]

---- Result was:
{error reading "sock01B57690": connection refused} {}
---- Result should have been (glob matching):
{error reading "sock*": socket is not connected} {connection refused}
==== socket-14.7.2 FAILED



==== socket-14.11.0 pending [socket -async] and blocking [puts], no listener, no flush FAILED
==== Contents of test case:

        set sock [socket -async localhost [randport]]
        fconfigure $sock -blocking 0
        puts $sock ok
        fileevent $sock writable {set x 1}
        vwait x
        close $sock

---- Result was:
socket is not connected
---- Result should have been (exact matching):
broken pipe
==== socket-14.11.0 FAILED



==== socket-14.11.1 pending [socket -async] and blocking [puts], no listener, flush FAILED
==== Contents of test case:

        set sock [socket -async localhost [randport]]
        fconfigure $sock -blocking 0
        puts $sock ok
        flush $sock
        fileevent $sock writable {set x 1}
        vwait x
        close $sock

---- Result was:
socket is not connected
---- Result should have been (exact matching):
broken pipe
==== socket-14.11.1 FAILED