[CopyPaste] We DON'T copy-paste as a professional programmer

Yesterday I used almost half day to debug a strange problem: When we set a specific timeout for watchdog timeout via a uart port in our application, the checking of the ack from the other end will not pass. But our HW engineer has a tiny tool which can do that too will be OK.

Later I found the decoding is wrong with pppDecode ( which was copied from a blog by someone, http://blog.csdn.net/wangxg_7520/article/details/2488491) . 

Let's have a look at the function:

int pppDecode(unsigned char * buf, int len) {
  unsigned char * pi, *po;
  int i, olen;
  unsigned char obuf[BUF_LEN];

  if(len > BUF_LEN) {
    return -1;
  }

  memset(obuf, 0, BUF_LEN);
  pi = buf;
  po = obuf;
  olen = len;

  for(i=0; i<len; i++) {
   if(*pi == PPP_FRAME_ESC) {

    /* skip the escape byte */
    pi++;
    olen--;

   /* xor the 6th bit */
   *po = *pi ^ PPP_FRAME_ENC;
   }
   else {
    *po = *pi;
   }
   pi++;
   po++;
}

The pi may be added twice in one loop. While the loop control is the i variable. Thus pi may exceed the buf area and the behavior depends on the data after buf... 

Commented to the blog author, hope he can update soon.

Final words, as a professional programmer, never copy-paste code directly from internent without understanding it!