Hey guys!

I am writing a multiplayer game and I'm going on to the networking now. But I run into an issue.

My C# server is not reading the bytes sent from my java client correctly.

This is the code on both sides:

Client:
public void sendPacket() {
		try {
			dos = new DataOutputStream(server.getOutputStream());
			dos.writeBytes(packet.getPacketID());
			dos.flush();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

Server:
NetworkStream playerStream = client.GetStream();
			
int recv;
byte[] data = new byte[client.ReceiveBufferSize];
			
Console.WriteLine("Player has connected: {0}", client.Client.RemoteEndPoint);
if (client.Client.Available > 0) {
	PacketReader s = new PacketReader(data);
	s.s(); // This does "ReadString()" from BinaryReader.
}

My Strings show up blank in the console. Any help?

// The 32-bit integer, 4779:
Little endian:  AB 12 00 00
Big endian:     00 00 12 AB


// The string, "Kosher-Yosher™":
UTF-8:
4B 6F 73 68 65 72 2D 59 6F 73 68 65 72 E2 84 A2

UTF-16, big endian, with byte order mark: 
FE FF 00 4B 00 6F 00 73 00 68 00 65 00 72 00 2D
00 59 00 6F 00 73 00 68 00 65 00 72 21 22

UTF-16, little endian, with byte order mark:
FF FE 4B 00 6F 00 73 00 68 00 65 00 72 00 2D 00
59 00 6F 00 73 00 68 00 65 00 72 00 22 21

// Java
string s = packet.getPacketID();
dos.writeInt(s.length);
dos.writeBytes(s);
dos.flush();


// C#
int length = packetReader.ReadInt32();
string s = Encoding.ASCII.GetString(packetReader.ReadBytes(length));

// Java
int packetId = whatever;
dos.writeInt(packetId);

// C#
int packetId = packetReader.ReadInt32();

BinaryReader.ReadString expects a string in a different format than what Java is writing.

Java's writeBytes function writes a sequence of bytes, where each byte is the low 8 bits of each char in the string. So basically, it'll work on ASCII strings. However, C#'s BinaryReader.ReadString expects the string's length in VLQ form ( https://en.wikipedia.org/wiki/Variable-length_quantity ) to appear before the characters.

You can use C#'s BinaryReader.ReadChars, or BinaryReader.ReadBytes followed by Encoding.ASCII.GetString instead to avoid that problem. However, you will need to write the length manually, otherwise you won't know how many chars to read. So your code would look something like this:

// Java
string s = packet.getPacketID();
dos.writeInt(s.length);
dos.writeBytes(s);
dos.flush();


// C#
int length = packetReader.ReadInt32();
string s = Encoding.ASCII.GetString(packetReader.ReadBytes(length));

Alternatively, if you want to use an integer as your packet id instead of a string, it's much easier:

// Java
int packetId = whatever;
dos.writeInt(packetId);

// C#
int packetId = packetReader.ReadInt32();

The server still prints out a blank string even I use it exactly how you did...

The server still prints out a blank string even I use it exactly how you did...

The server still prints out a blank string even I use it exactly how you did...

Can you show us all of your code between the point where you read the packetId and print it out to the console? Your original post doesn't contain anything that will try to print the packetId to the console.

Server:
public class PacketReader : BinaryReader
	{
		public PacketReader(NetworkStream str) : base(str) {
		}
		
		public void s() {
			int le = ReadInt32();
			Console.WriteLine(le); // Prints a big int.
			string m = Encoding.ASCII.GetString(ReadBytes(le)); // Doesn't print anything out but causes an exception when i close the client.
			Console.WriteLine(m);
		}
 	}

Client:
public void sendPacket() {
		try {
			dos = new DataOutputStream(server.getOutputStream());
			dos.writeInt(packet.getPacketID().length());
			dos.writeBytes(packet.getPacketID());
			dos.flush();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

These two show how the bytes are sent, and how the server tries to read them.

And...

Server:
public void handleConnection() {
			NetworkStream playerStream = client.GetStream();
			
			int recv;
			byte[] data = new byte[1024];
			
			Console.WriteLine("Player has connected: {0}", client.Client.RemoteEndPoint);
			if (client.Client.Available > 0) {
				PacketReader s = new PacketReader(playerStream);
				s.s();
			}
		}

This is currently how it checks if the data is available and uses "s.s" to print it out.

What does WriteLine(le) print out? Is it correct?

The server prints out a much bring length then the client does when testing...