code: public static int findPreamble(byte[] buf, int start, int len) {
          int e = start + len - PREAMBLE.length + 1;
  
          OUTER:
          for (int i=start; i<e; i++) {
              if (buf[i]==PREAMBLE[0]) {
                  // check for the rest of the match
                  for (int j=1; j<PREAMBLE.length; j++) {
                      if (buf[i+j]!=PREAMBLE[j])
                          continue OUTER;
                  }
                  return i; // found it
              }
          }
          return -1; // not found
      }
docs: Locates the preamble in the given buffer.