socket communication in java

Question

this.cin = new DataInputStream(this.csocket.getInputStream()); 

public class ReceiveMessage extends Thread{             
    public void run(){
        while(stop == false)
            try {
                if(cin.available()>0)
                    receMessage();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
}

    // choke, unchoke, interested, notinterested, have, bitfield, request, piece
    public void receMessage(){
        int rv=0;
        byte[] length = new byte[4];        // total length
        try {
            rv = cin.read(length, 0, 4);
        } catch (IOException e) {
            e.printStackTrace();
        }

        if(rv <=0)              
            return;         

        byte[] type = new byte[1];
        try {
            cin.read(type, 0, 1);
        } catch (IOException e) {
            e.printStackTrace();
        }

        int size = byte2int(length) -4 -1; //size of payload            
        clearPayload();
        if(size > 0){               
            try {                   
                cin.read(this.payload, 0, size);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        byte mtype = type[0];
        switch(mtype){
            case (byte)0:
                receNoPayload((byte)0);
                break;
            case 1:
                receNoPayload((byte)1);
                break;
            case 2:
                receNoPayload((byte)2);
                break;
            case 3:
                receNoPayload((byte)3);
                break;
            case 4:
                receHave(payload);
                break;
            case 5: 
                receBitField(payload);
                break;
            case 6:
                receRequest(payload);
                break;
            case 7:             
                recePiece(payload, size);
                break;
            default:
                System.out.println("wrong message type!");
        }       

}

the code above is used to read data from socket. I create a thread to read data from socket.and then analyze the data according the type of message contained in data. Now, the problem is if I transfer 100 bytes into socket, I can do everything correctly; however, if I transfer 1000 bytes into socket, sometimes, the data read out is wrong. for example, the variable type cannot be greater than 7 normally. But now the type read out is greater than 7, which is wrong.

in both case, I do not change anything, except the size of data transferred.

please help me, thank you! I have done everything I can do, but i still cannot figure it out.

Answer 1

1. Get rid of the available() call. The read() will block if there is no data. At present you're just burning the CPU.

2. Check the result of each read. You can't assume it filled the buffer. Or use DataInputStream.readFully() instead.