[Tcl-bugs] [Bug #119307] Tcl's fileevent callback on a socket does not work the same

[<no...@so...>]

Bug #119307, was updated on 2000-Oct-25 22:10
Here is a current snapshot of the bug.

Project: Tcl
Category: Sockets
Status: Open
Resolution: None
Bug Group: 8.2.1
Priority: 5
Submitted by: nobody
Assigned to : nobody
Summary: Tcl's fileevent callback on a socket does not work the same 

Details: OriginalBugID: 3319 Bug
Version: 8.2.1
SubmitDate: '1999-11-05'
LastModified: '1999-11-11'
Severity: MED
Status: UnAssn
Submitter: techsupp
ChangedBy: hobbs
OS: Linux-Red Hat
OSVersion: RedHat 5.2 (intel)
FixedDate: '2000-10-25'
ClosedDate: '2000-10-25'


Name:
Mo DeJong

ReproducibleScript:
# First, start the "server" and listen for connections.
# When a connection arrives just close the socket.

set port 6789

proc incomingConnection { stream addr port } {
    puts "incomingConnection from $addr $port"
    close $stream
}

set server [socket -server incomingConnection $port]

# Now create the "client" socket which makes a connection
# This causes the error {error writing "sock7": broken pipe}

proc canWrite { } {
  global socket
  if {[eof $socket]} {
    puts "EOF ON SOCKET"
  }

  puts "Writing to socket"
  puts $socket "CLOSE"
}

set socket [socket localhost $port]
fconfigure $socket -buffering line -blocking 0
fileevent $socket writable canWrite

vwait forever

ObservedBehavior:
This generates an error on UNIX systems when the socket is closed on the
server side. The client tries to write when it gets a fileevent writable
event, and this generates and during the write() call because the socket
was closed.


It does not work on these systems:
RedHat Linux 5.2 with Tcl 8.2.1
Solaris 5.6 with Tcl 8.2.1
IRIX 6.2 with Tcl 8.2.1

But under NT with Tcl 8.2.1, the extra fileevent
callback is not generated.

DesiredBehavior:
A fileevent writable callback should not be generated on a closed socket
under UNIX systems.



Newsgroup reports indicate that NT has the incorrect behavior. 
-- 11/11/1999 hobbs

Follow-Ups:

Date: 2001-Jan-22 12:07
By: hinteger

Comment:
I thought the right way to use callbacks is always to check for eof on both
readable and writable channels, that's how all my scripts do and I don't
have any problems with that. The man page is quite clear about that for
readable channels and not so clear for writable, but I think eof _is_ an
error condition.
-------------------------------------------------------

Date: 2001-Jan-16 06:21
By: dkf

Comment:
It looks to me like the behaviour described as being erroneous is quite
possible, since the [socket] command (as written) returns a connected
socket, meaning that the server will have had a chance to close the socket
off.    Either the socket being opened or being closed would be sufficient
reason to trigger the writable callback (which is also called when the
socket is in an error condition, e.g. closed.)

The real question is why are no callbacks being performed for the channel
at the Tcl end under Windows?
-------------------------------------------------------

For detailed info, follow this link:
http://sourceforge.net/bugs/?func=detailbug&bug_id=119307&group_id=10894