NAME¶
udp - Create UDP sockets in Tcl
SYNOPSIS¶
package require
Tcl 8.2
package require
udp 1.0
udp_open ?
port?
udp_conf sock host port
udp_conf sock ?-myport? ?-remote? ?-peer?
?-broadcast bool? ?-ttl count?
udp_conf ?
-mcastadd groupaddr?
udp_conf ?
-mcastdrop groupaddr?
udp_peek sock ?
buffersize?
DESCRIPTION¶
This package provides support for using UDP through Tcl. The package provides a
new channel type and attempts to permit the use of packet oriented UDP over
stream oriented Tcl channels. The package defined three commands but
udp_conf should be considered depreciated in favour of the standard Tcl
command
fconfigure.
COMMANDS¶
- udp_open ?port?
- udp_open will open a UDP socket. If port is
specified the UDP socket will be opened on that port. Otherwise the system
will choose a port and the user can use the udp_conf command to
obtain the port number if required.
- udp_conf sock host port
- udp_conf in this configuration is used to specify
the remote destination for packets written to this sock. You must
call this command before writing data to the UDP socket.
- udp_conf sock ?-myport?
?-remote? ?-peer? ?-broadcast bool? ?-ttl
count?
- In addition to being used to configure the remote host, the
udp_conf command is used to obtain information about the UDP
socket.
- -myport
- Returns the local port number of the socket.
- -remote
- Returns the remote hostname and port number as set using
udp_conf sock host port.
- -peer
- Returns the remote hostname and port number for the packet
most recently received by this socket.
- -broadcast ?boolean?
- UDP packets can listen and send on the broadcast address.
For some systems a flag must be set on the socket to use broadcast. With
no argument this option will return the broadcast setting. With a boolean
argument the setting can be modified.
- -ttl ?count?
- The time-to-live is given as the number of router hops the
packet may do. For multicast packets this is important in specifying the
distribution of the packet. The system default for multicast is 1 which
restricts the packet to the local subnet. To permit packets to pass
routers, you must increase the ttl. A value of 31 should keep it within a
site, while 255 is global.
- udp_conf ?-mcastadd groupaddr?
- udp_conf ?-mcastdrop groupaddr?
- tcludp sockets can support IPv4 multicast
operations. To recieve multicast packets the application has to notify the
operating system that it should join a particular multicast group. These
are specified as addresses in the range 224.0.0.0 to 239.255.255.255.
- udp_peek sock ?buffersize?
- Examine a packet without removing it from the buffer. This
function is not available on windows.
EXAMPLES¶
# Send data to a remote UDP socket
proc udp_puts {host port} {
set s [udp_open]
fconfigure $s -remote [list $host $port]
puts $s "Hello, World"
close $f
}
# A simple UDP server
package require udp
proc udpEventHandler {sock} {
set pkt [read $sock]
set peer [fconfigure $sock -peer]
puts "$peer: [string length $pkt] {$pkt}"
return
}
proc udp_listen {port} {
set srv [udp_open $port]
fconfigure $srv -buffering none -translation binary
fileevent $srv readable [list ::udpEventHandler $srv]
puts "Listening on udp port: [fconfigure $srv -myport]"
return $srv
}
set sock [udp_listen 53530]
vwait forever
close $sock
# A multicast demo.
proc udpEvent {chan} {
set data [read $chan]
set peer [fconfigure $chan -peer]
puts "$peer [string length $data] '$data'"
if {[string match "QUIT*" $data]} {
close $chan
set ::forever 1
}
return
}
set group 224.5.1.21
set port 7771
set s [udp_open $port]
fconfigure $s -buffering none -blocking 0
fconfigure $s -mcastadd $group -remote [list $group $port]
fileevent $s readable [list udpEvent $s]
puts -nonewline $s "hello, world"
set ::forever 0
vwait ::forever
exit
HISTORY¶
Some of the code in this extension is copied from Michael Miller's tcludp
package. (
http://www.neosoft.com/tcl/ftparchive/sorted/comm/tcludp-1.0/)
Compared with Michael's UDP extension, this extension provides Windows support
and provides the ability of using 'gets/puts' to read/write the socket. In
addition, it provides more configuration ability.
Enhancements to support binary data and to setup the package for the Tcl
Extension Architecture by Pat Thoyts.
SEE ALSO¶
socket(3tcl)
KEYWORDS¶
networking, socket, udp
COPYRIGHT¶
Copyright (c) 1999-2000 Columbia University; all rights reserved