ByteArrayInputStream question
Greetings everyone,
I'm working on a project to do a simple .txt file transfer over a UDP protocol. However we have to make it more reliable by calculating checksum's and sequence numbers and send ack's via the stop and wait protocol (rdt 2.2). So here's my question:
In my receiever class I have this:
publicbyte[] rdt_receive(){
byte[] data =newbyte[maxPacketSize];
try{
DatagramPacket recievedPacket =new DatagramPacket(data,
data.length);
// data recieving part
clientSocket.receive(recievedPacket);
ByteArrayInputStream bais =new ByteArrayInputStream(recievedPacket.getData());
DataInputStream dis =new DataInputStream(bais);
int seqNum = dis.read();
System.out.println(seqNum);
short checkSum = dis.readShort();
System.out.println(checkSum);
/*
System.out.println("Sequence Number of packet received: " + seqNum);
System.out.println("Sequence Number Expected: " + expectedSeqNum);
if(seqNum != expectedSeqNum){
System.err.println("Woops...wrong sequence number");
}*/
int i = 0;
byte newest = dis.readByte();
while(Byte.valueOf(newest) !=null){
data[i] = newest;
newest = dis.readByte();
i++;
}
for(int j=0; j<data.length; j++){
System.out.print(data[i] +" ");
}
//short ourCheckSum = getCheckSum(data);
//System.out.println("CheckSum of packet received: " + checkSum);
//System.out.println("CheckSum we calculated " + ourCheckSum);
expectedSeqNum++;
}catch (Exception e){
System.err.println(e.getMessage() +" receive method");
}
return data;
}
However when I read from the bais, I watch the position while debugging and my i in the while loop increases slower than the bais position counter. I have already figured out that it goes like this:
dis.readInt() increases the position counter by 1
dis.readShort() increases the position counter by 2
The checksum is calculated as a 16 bit short so naturally that's 2 bytes so I guess the +2 on the counter is acceptable, but I can't figure out how to get this receive method to work. If anyone can give me any advice/needs me to post more code, just let me know.
Oh p.s. the error I'm getting is Null (because the position counter goes higher than the InputStream)
Thanks,
Alex
Message was edited by:
thequietone>
