SocketChannel in Java sends data, but it doesn't get to destination application
- by Peterson
Hi Everybody,
I'm suffering a lot to create a simple ChatServer in Java, using the NIO libraries. Wonder if someone could help me.
I am doing that by using SocketChannel and Selector to handle multiple clients in a single thread. The problem is: I am able to accept new connections and get it's data, but when I try to send data back, the SocketChannel simply doesn't work. In the method write(), it returns a integer that is the same size of the data i'm passing to it, but the client never receives that data. Strangely, when I close the server application, the client receives the data. It's like the socketchannel maintains a buffer, and it only get flushed when I close the application.
Here are some more details, to give you more information to help. I'm handling the events in this piece of code:
private void run() throws IOException {
ServerSocketChannel ssc = ServerSocketChannel.open();
// Set it to non-blocking, so we can use select
ssc.configureBlocking( false );
// Get the Socket connected to this channel, and bind it
// to the listening port
this.serverSocket = ssc.socket();
InetSocketAddress isa = new InetSocketAddress( this.port );
serverSocket.bind( isa );
// Create a new Selector for selecting
this.masterSelector = Selector.open();
// Register the ServerSocketChannel, so we can
// listen for incoming connections
ssc.register( masterSelector, SelectionKey.OP_ACCEPT );
while (true) {
// See if we've had any activity -- either
// an incoming connection, or incoming data on an
// existing connection
int num = masterSelector.select();
// If we don't have any activity, loop around and wait
// again
if (num == 0) {
continue;
}
// Get the keys corresponding to the activity
// that has been detected, and process them
// one by one
Set keys = masterSelector.selectedKeys();
Iterator it = keys.iterator();
while (it.hasNext()) {
// Get a key representing one of bits of I/O
// activity
SelectionKey key = (SelectionKey)it.next();
// What kind of activity is it?
if ((key.readyOps() & SelectionKey.OP_ACCEPT) ==
SelectionKey.OP_ACCEPT) {
// Aceita a conexão
Socket s = serverSocket.accept();
System.out.println( "LOG: Conexao TCP aceita de " + s.getInetAddress() + ":" + s.getPort() );
// Make sure to make it non-blocking, so we can
// use a selector on it.
SocketChannel sc = s.getChannel();
sc.configureBlocking( false );
// Registra a conexao no seletor, apenas para leitura
sc.register( masterSelector, SelectionKey.OP_READ );
} else if ( key.isReadable() ) {
SocketChannel sc = null;
// It's incoming data on a connection, so
// process it
sc = (SocketChannel)key.channel();
// Verifica se a conexão corresponde a um cliente já existente
if((clientsMap.getClient(key)) != null){
boolean closedConnection = !processIncomingClientData(key);
if(closedConnection){
int id = clientsMap.getClient(key);
closeClient(id);
}
} else {
boolean clientAccepted = processIncomingDataFromNewClient(key);
if(!clientAccepted){
// Se o cliente não foi aceito, sua conexão é simplesmente fechada
sc.socket().close();
sc.close();
key.cancel();
}
}
}
}
// We remove the selected keys, because we've dealt
// with them.
keys.clear();
}
}
This piece of code is simply handles new clients that wants to connect to the chat. So, a client makes a TCP connection to the server, and once it gets accepted, it sends data to the server following a simply text protocol, informing his id and asking to get registrated to the server. I handle this in the method processIncomingDataFromNewClient(key). I'm also keeping a map of clients and its connections in a data structure similar to a hashtable. I? doing that because I need to recover a client Id from a connection and a connection from a client Id. This is can be shown in: clientsMap.getClient(key).
But the problem itself resides in the method processIncomingDataFromNewClient(key). There, I simply read the data that the client sent to me, validate it, and if it's ok, I send a message back to the client to tell that it is connected to the chat server.
Here is a similar piece of code:
private boolean processIncomingDataFromNewClient(SelectionKey key){
SocketChannel sc = (SocketChannel) key.channel();
String connectionOrigin = sc.socket().getInetAddress() + ":" + sc.socket().getPort();
int id = 0; //id of the client
buf.clear();
int bytesRead = 0;
try {
bytesRead = sc.read(buf);
if(bytesRead<=0){
System.out.println("Conexão fechada pelo: " + connectionOrigin);
return false;
}
System.out.println("LOG: " + bytesRead + " bytes lidos de " + connectionOrigin);
String msg = new String(buf.array(),0,bytesRead);
// Do validations with the client sent me here
// gets the client id
}catch (Exception e) {
e.printStackTrace();
System.out.println("LOG: Oops. Cliente não conhece o protocolo. Fechando a conexão: " + connectionOrigin);
System.out.println("LOG: Primeiros 10 caracteres enviados pelo cliente: " + msg);
return false;
}
}
} catch (IOException e) {
System.out.println("LOG: Erro ao ler dados da conexao: " + connectionOrigin);
System.out.println("LOG: "+ e.getLocalizedMessage());
System.out.println("LOG: Fechando a conexão...");
return false;
}
// If it gets to here, the protocol is ok and we can add the client
boolean inserted = clientsMap.addClient(key, id);
if(!inserted){
System.out.println("LOG: Não foi possível adicionar o cliente. Ou ele já está conectado ou já têm clientes demais. Id: " + id);
System.out.println("LOG: Fechando a conexão: " + connectionOrigin);
return false;
}
System.out.println("LOG: Novo cliente conectado! Enviando mesnsagem de confirmação. Id: " + id + " Conexao: " + connectionOrigin);
/* Here is the error */
sendMessage(id, "Servidor pet: connection accepted");
System.out.println("LOG: Novo cliente conectado! Id: " + id + " Conexao: " + connectionOrigin);
return true;
}
And finally, the method sendMessage(SelectionKey key) looks like this:
private void sendMessage(int destId, String msg) {
Charset charset = Charset.forName("ISO-8859-1");
CharBuffer charBuffer = CharBuffer.wrap(msg, 0, msg.length());
ByteBuffer bf = charset.encode(charBuffer);
//bf.flip();
int bytesSent = 0;
SelectionKey key = clientsMap.getClient(destId);
SocketChannel sc = (SocketChannel) key.channel();
try {
/
int total_bytes_sent = 0;
while(total_bytes_sent < msg.length()){
bytesSent = sc.write(bf);
total_bytes_sent += bytesSent;
}
System.out.println("LOG: Bytes enviados para o cliente " + destId + ": "+ total_bytes_sent + " Tamanho da mensagem: " + msg.length());
} catch (IOException e) {
System.out.println("LOG: Erro ao mandar mensagem para: " + destId);
System.out.println("LOG: " + e.getLocalizedMessage());
}
}
So, what is happening is that the server, when send a message, prints something like this:
LOG: Bytes sent to the client: 28 Size of the message: 28
So, it tells that it sent the data, but the chat client keeps blocking, waiting in the recv() method. So, the data never gets to it. When I close the server application, though, all the data appears in the client. I wonder why.
It is important to say that the client is in C and the server JAVA, and I'm running both in the same machine, an Ubuntu Guest in virtualbox under windows. I also run both under windows host and under linuxes hosts, and keep getting the same strange problem.
I'm sorry for the great lenght of this question, but I already searched a lot of places for an answer, found a lot of tutorials and questions, including here at StackOverflow, but coundn't find a reasonable explanation. I am really not liking this Java NIO, and i saw a lot of people complaining about it too. I am thinking that if I had done that in C it would have been a lot easier :-D
So, if someone could help me and even discuss this behavor, it would be great! :-)
Thanks everybody in advance,
Péterson
