TCP-Server reading a packet structure from a non Java client

Question

So I wanna communicate between a C++ client and a Java server.
So far so good (yeah I know about the Endiness prob) but I would like to read a defined structure on my serverside which was defined on clientside.

Let's say my client sends a packet in this structure:

char *pLoginData = new char[512];
// ...
char *packet = pLoginData;
*(WORD*)pLoginData = (usernameLength + 1 + passwordLength + 1);

pLoginData += 2;

strcpy((char*)(pLoginData), username.c_str());
pLoginData += usernameLength + 1;

strcpy((char*)(pLoginData), password.c_str());
pLoginData += passwordLength + 1;

// now send it
m_iResult = send(connectSocket, packet, *(WORD*)(packet) + 2, 0);

On my serverside how far I got is:

// init socket, init DataInputStream..
// ...
messageByte[0] = in.readByte(); // defined as: byte[] messageByte = new byte[1000];
System.out.println("Packet len: " + messageByte[0]);

bytesRead = in.read(messageByte);
msg += new String(messageByte, 0, bytesRead); // defined as: String msg = null;

System.out.println(msg);

Output is unfortunately:

Packet len: 16
null testuser testpw

(there is a space after testpw, why? because look on how the client constructs the packet)
As you can see, my output contains the word "null" (dunno why?), but you see aswell that the word "null" isn't counted, cause packet len returns 16 which is: username (space) pw (space) (testuser testpw )

Hope you guys could help me out here :)
Thanks in advance!

Federico klez Culloca · Accepted Answer · 2018-02-21 13:25:16Z

2

As you said in a comment in the code, you're defining msg as a null string and then appending to it.

You should declare msg as an empty string.

answered Feb 21, 2018 at 13:25

Federico klez Culloca

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