Edge case errors in multipart binary file uploads

[shaunkime]

I found this error in the lacewing version of the multipart-parser-c, but I think that it also resides in your original version.

When in the s_part_data_almost_boundary condition when dealing with the test for a LF character fails, there are two current bad edge conditions, when i is 0 or when i is_last. Additionally, in the s_part_data_boundary condition when the boundary does not equal the current index, there is an edge condition when i is_last as well.

Cutting & pasting my local changes with debugging logic still in place:

multipart_parser.c(228)
/* fallthrough */
case s_part_data:
multipart_log("s_part_data");
if (c == CR) {
EMIT_DATA_CB(part_data, buf + mark, i - mark);
mark = i;
p->state = s_part_data_almost_boundary;
p->lookbehind[0] = CR;
break;
}
if (is_last)
EMIT_DATA_CB(part_data, buf + mark, (i - mark) + 1);
break;

case s_part_data_almost_boundary:
multipart_log("s_part_data_almost_boundary");
if (c == LF) {
p->state = s_part_data_boundary;
p->lookbehind[1] = LF;
p->index = 0;
break;
}
EMIT_DATA_CB(part_data, p->lookbehind, 1);
p->state = s_part_data;

//  sckime edit  begin
if (i == 0)
{
  mark = i; // The new buffer mark is the start, would otherwise be -1
}
else if (is_last)
{
  mark = i; 
  EMIT_DATA_CB(part_data, buf + mark, (i - mark) + 1); // No one will output this data otherwise.
}
else
//  sckime edit  end
{
  mark = i --;
}
break;

case s_part_data_boundary:
multipart_log("s_part_data_boundary");
if (p->multipart_boundary[p->index] != c) {
EMIT_DATA_CB(part_data, p->lookbehind, 2 + p->index);
p->state = s_part_data;
mark = i --;

  // sckime edit begin
  if (is_last)
  {
    mark = i;
    EMIT_DATA_CB(part_data, buf + mark, (i - mark) + 1);  // No one will output this data otherwise.
  }
  //sckime edit end
  break;
}
p->lookbehind[2 + p->index] = c;
if ((++ p->index) == p->boundary_length) {
    NOTIFY_CB(part_data_end);
    p->state = s_part_data_almost_end;
}
break;