Shootout Echo

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-- 2003-09 (Lua 5.0)

-- lua -lposix -lsocket echo.lua [number]



data = 'Hello there sailor\n'

dlen = string.len(data)



-- this documents the ways a tcp receive() can go wrong.  it should

-- not be called if the 2nd result of calling receive() == nil, but it

-- guards against the possibility even so.

function socket_receive_error(err)

   if err == nil then

      print'socket_receive_error(): err == nil, oops!'

   elseif err == 'closed' then

      print'<socket>:receive(): connection closed'

      return

   elseif err == 'timeout' then

      print'<socket>:receive(): connection timed out'

   else

      error('<socket>:receive(): error: '..err)

   end

end



function server_sock()

   local server,err = socket.bind('127.0.0.1',0)

   assert(server,err)

   return server

end



function get_port(sock)

   local _,port = sock:getsockname()

   return port

end



function client_sock(port)

   local client,err = socket.connect('127.0.0.1',port)

   assert(client,err)

   return client

end



function echo_client(n,port)

   local s = client_sock(port)

   for i=1,n do

      s:send(data)

      local d,err = s:receive(dlen)

      if err then

         socket_receive_error(err)

         break

      end

      if d ~= data then error('server reply: '..d) end

   end

   s:close()

end



function echo_server(n)

   local ssock = server_sock()

   local pid = posix.fork()

   if pid == 0 then

      echo_client(n,get_port(ssock)) -- child is client

   else

      local n = 0

      local client,err = ssock:accept()

      while true do

         local data,err = client:receive(dlen)

         if err then

            socket_receive_error(err)

            break

         end

         n = n + string.len(data)

         client:send(data)

      end

      print('server received '..n..' bytes')

   end

end



-- insist on a proper argument if one's present, no silent corrections

if arg and arg[1] then

   n = tonumber(arg[1])

   if not n then error('arg must be a number') end

else

   n = 1

end

echo_server(n)

--SteveElkins