/**
 * call-seq:
 *    parser.execute(req_hash, data, start) -> Integer
 *
 * Takes a Hash and a String of data, parses the String of data filling in the Hash
 * returning an Integer to indicate how much of the data has been read.  No matter
 * what the return value, you should call HttpParser#finished? and HttpParser#error?
 * to figure out if it's done parsing or there was an error.
 * 
 * This function now throws an exception when there is a parsing error.  This makes 
 * the logic for working with the parser much easier.  You can still test for an 
 * error, but now you need to wrap the parser with an exception handling block.
 *
 * The third argument allows for parsing a partial request and then continuing
 * the parsing from that position.  It needs all of the original data as well 
 * so you have to append to the data buffer as you read.
 */
VALUE HttpParser_execute(VALUE self, VALUE req_hash, VALUE data, VALUE start)
{
  http_parser *http = NULL;
  int from = 0;
  char *dptr = NULL;
  long dlen = 0;

  DATA_GET(self, http_parser, http);

  from = FIX2INT(start);
  dptr = RSTRING(data)->ptr;
  dlen = RSTRING(data)->len;
  
  if(from >= dlen) {
    rb_raise(eHttpParserError, "Requested start is after data buffer end.");
  } else {
    http->data = (void *)req_hash;
    http_parser_execute(http, dptr, dlen, from);
    
    VALIDATE_MAX_LENGTH(http_parser_nread(http), HEADER);
    
    if(http_parser_has_error(http)) {
      rb_raise(eHttpParserError, "Invalid HTTP format, parsing fails.");
    } else {
      return INT2FIX(http_parser_nread(http));
    }
  }
}