Question

Suppose I get from the network a sequence of bytes in the following order:
X X X X = X X X X = X X X X = … and so on
you can notice immediately the pattern (a message is a sequence of 5 bytes: “X X X X =
X can be any number except ‘=’ of course)

Now, the transmission occur periodically.
In some point my application is starting and getting the bytes sequence

What is the best algorithm for taking those bytes and framing them to 5 bytes messages?
There are two problems:
1. How do you find the first message? I guess I need to drop some bytes till I get ‘=’ right?
2. How the application suppose to handle a pause of transimmision and a new start.

Answer 1

The simplest way is to use a blocking read (which is the most common because its the simplest) to read 5 bytes at a time.

Normally, you wouldn’t assume you have junk data at the start, and just read everything. If you have a header, I would read that too.

DataInputStream dis = new DataInputStream(socket stream);
byte[] bytes = new byte[5];

int sep;
do {
  dis.readFully(bytes);
  process(bytes);
} while((sep = dis.read()) == '=');
if (sep > 0)
   System.err.println("Unexpected character "+ (char) sep));