The function has two major parts - branches of the outermost IF. In the ELSE 
branch there is another IF with condition, which is always true, considering 
where it appears. Thus, a big portion of code in the ELSE part of the inner IF 
is effectively disabled. 

if (input->buf != NULL) {
   ...
   ...
} else {  
   // input->buf is NULL here!
   if ((input->length == 0) || (input->buf == NULL)) {
      ...
   } else {
      // UNREACHABLE BLOCK OF CODE
   }
}

Some compilers are smart enough to not compile unreached code (though not 
issuing a warning), but this fact is still worrying.