I shall explain these programs line by line.
Before that in case any of you wondered this is how you would run it.
$ lua echosrvr.lua
In another terminal
$ lua echoclnt.lua
hi
will get printed on both sides as the text will be echoed back thro' the UDP
socket.
I hope you guys got that far at least if not any farther. ;)
Let us dissect the program presently.
My comments begin with a <comment> tag.
1) echoclnt.lua
-- -----------------------------------------------------------------------------
-- UDP sample: echo protocol client
-- LuaSocket sample files
-- Author: Diego Nehab
-- RCS ID: $Id: echoclnt.lua,v 1.10 2005/01/02 22:44:00 diego Exp $
-----------------------------------------------------------------------------
<comment> All comments in lua start with '--'
local socket = require("socket")
<comment> we import the 'socket' module similar to perl 'use' or python 'import'
host = host or "localhost"
port = port or 1234
if arg then
host = arg[1] or host
port = arg[2] or port
end
<comment> The above lines are reasonably straight forward. arg[1] to
arg[n] stand for
<comment> command line arguments. Also note if then ... end. You also have
<comment> while do ... end and for do ... end
host = socket.dns.toip(host)
<comment> You get IP from DNS. You can do print(host) and check it
here if you want
udp = assert(socket.udp())
assert(udp:setpeername(host, port))
<comment> You see assert() in action here. If the value is empty
program will exit I think.
<comment> You can also do udp = socket.udp(). You are opening a UDP socket.
<comment> setpeername() is necessary I think in lua. Not sure
print("Using remote host '" ..host.. "' and port " .. port .. "...")
<comment> print() function like C printf or perl print or python
print. Just like python you also
<comment> an interactive interpreter. Just type lua. You also have an
alias for print called '='.
<comment> For example: lua>=3*5 will give 15
while 1 do
line = io.read()
if not line or line == "" then os.exit() end
assert(udp:send(line))
dgram = assert(udp:receive())
print(dgram)
end
<comment> While loop in action. io.read() and io.write() will read and
write from/to STDIN/STDOUT.
<comment> Exit on empty line and invoke the send() function of udp table.
<comment> Then receive...
Now let us move on to the server.
Just copy paste this and use this server with it:
2)echosrvr.lua
-----------------------------------------------------------------------------
-- UDP sample: echo protocol server
-- LuaSocket sample files
-- Author: Diego Nehab
-- RCS ID: $Id: echosrvr.lua,v 1.12 2005/11/22 08:33:29 diego Exp $
-----------------------------------------------------------------------------
local socket = require("socket")
host = host or "127.0.0.1"
port = port or 1234
if arg then
host = arg[1] or host
port = arg[2] or port
end
<same as above>
print("Binding to host '" ..host.. "' and port " ..port.. "...")
udp = assert(socket.udp())
assert(udp:setsockname(host, port))
assert(udp:settimeout(5))
<comment> In the server you have to bind. You also set a timeout
ip, port = udp:getsockname()
<comment> simultaneous assignment of two values like in perl or python
assert(ip, port)
<comment> Ensuing that both values are defined and usable
print("Waiting packets on " .. ip .. ":" .. port .. "...")
<comment> You give arguments to print() or io.write() using ..
operator. Like %s in C and
<comment> % in python and . in perl.
while 1 do
dgram, ip, port = udp:receivefrom()
if dgram then
print("Echoing '" .. dgram .. "' to " .. ip .. ":" .. port)
udp:sendto(dgram, ip, port)
else
print(ip)
end
end
<comment> infinite loop. Please note the end placements to signify if
and while closing points
Please ask in case of doubts. This should get you started. Tomorrow we
will examine a lua
sample to print thumbnails of images. With that lua tutorial will end.;)
If I get time to learn this language properly I shall organize a one
day programme on lua within 2 months.
If you want to sponsor a hall, please mail me or Bharathi in private.
-Girish
--
Gayatri Hitech
web: http://gayatri-hitech.com
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