TCP receive problem w. Java Server

jcfinnerup · February 13, 2014, 3:47pm

Hi There!

I am developing a Java server to go along with an app, however i have run into the following problem:

I am using TCP to handle the client/server communication but for some reason, i am only able to send data to the Server but not receive a reply.

This is an example of my code which is super simple but for some reason doesn’t work and I am far beyond the point of staring myself blind, trying to fix it.

Lua:

function pushToServer(dataToSend)

local tcp = socket.tcp()

tcp:settimeout(2)

tcp:connect(xxxx, yyyyy);

tcp:send(dataToSend);

print(tcp:receive("*l"))

tcp:close()

end

Java:

// Read incoming

Socket clientSocket = serverSocket.accept();

in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

String jsonString = in.readLine();

// Reply

out = new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream()));

out.write(stringToReturn);

I have debugged the code enough to know that the java code is first executed when the Lua client’s connection is closed, and I cant seem to figure out why. The Server succesfully reads the data from the Lua client, but first when the client closes the connection. Then the Server writes a reply but cant, because the connection is closed, and so the client receives NIL.

I am convinced that the problem is probably really simple and i am just making a newbie mistake so i hope some of you ninjas can help.

Thanks in advance
Jens Finneurp

Develephant · February 20, 2014, 3:04pm

Hi,

This code is completely out of context as I just copied and pasted some of the relevant portions from an older project, but you basically need to make sure you’re continuously checking the TCP stream.

Again, this code won’t work as-is, it just to illustrate the behavior.

Hope it helps.

local socketlib = require( "socket" ) local json = require( "json" ) self.socket = socketlib.tcp() local success, msg = self.socket:connect( self.host, self.port ) if success then &nbsp;&nbsp;&nbsp;&nbsp;if self.inLobby == nil then &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;self.inLobby = true &nbsp;&nbsp;&nbsp;&nbsp;else &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;self.inLobby = false --in game &nbsp;&nbsp;&nbsp;&nbsp;end &nbsp;&nbsp;&nbsp;&nbsp;self.socket:settimeout( 0 ) &nbsp;&nbsp;&nbsp;&nbsp;self.socket:setoption( "tcp-nodelay", true ) &nbsp;&nbsp;&nbsp;&nbsp;self:start() end -- ... function Game:tick() &nbsp; &nbsp; local input, \_ = socketlib.select( { self.socket }, nil, 0 ) &nbsp; &nbsp; for \_, client in ipairs( input ) do &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp; &nbsp; local line, err, partial = client:receive('\*l') &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp; &nbsp; if not err then &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; local data = json.decode( line ) &nbsp; &nbsp; &nbsp; else &nbsp; &nbsp; &nbsp; &nbsp; if err == "closed" then &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; --kill connection &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; self:stop() &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; self.socket:close() &nbsp; &nbsp; &nbsp; &nbsp; end &nbsp; &nbsp; &nbsp; end &nbsp; &nbsp; end end function Game:start() &nbsp; if not self.processTimer then &nbsp; &nbsp; self.processTimer = timer.performWithDelay( 50, function() self:tick(); end, -1 ) &nbsp; end end &nbsp;

Develephant · February 20, 2014, 3:04pm

Hi,

This code is completely out of context as I just copied and pasted some of the relevant portions from an older project, but you basically need to make sure you’re continuously checking the TCP stream.

Again, this code won’t work as-is, it just to illustrate the behavior.

Hope it helps.

local socketlib = require( "socket" ) local json = require( "json" ) self.socket = socketlib.tcp() local success, msg = self.socket:connect( self.host, self.port ) if success then &nbsp;&nbsp;&nbsp;&nbsp;if self.inLobby == nil then &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;self.inLobby = true &nbsp;&nbsp;&nbsp;&nbsp;else &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;self.inLobby = false --in game &nbsp;&nbsp;&nbsp;&nbsp;end &nbsp;&nbsp;&nbsp;&nbsp;self.socket:settimeout( 0 ) &nbsp;&nbsp;&nbsp;&nbsp;self.socket:setoption( "tcp-nodelay", true ) &nbsp;&nbsp;&nbsp;&nbsp;self:start() end -- ... function Game:tick() &nbsp; &nbsp; local input, \_ = socketlib.select( { self.socket }, nil, 0 ) &nbsp; &nbsp; for \_, client in ipairs( input ) do &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp; &nbsp; local line, err, partial = client:receive('\*l') &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp; &nbsp; if not err then &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; local data = json.decode( line ) &nbsp; &nbsp; &nbsp; else &nbsp; &nbsp; &nbsp; &nbsp; if err == "closed" then &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; --kill connection &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; self:stop() &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; self.socket:close() &nbsp; &nbsp; &nbsp; &nbsp; end &nbsp; &nbsp; &nbsp; end &nbsp; &nbsp; end end function Game:start() &nbsp; if not self.processTimer then &nbsp; &nbsp; self.processTimer = timer.performWithDelay( 50, function() self:tick(); end, -1 ) &nbsp; end end &nbsp;