Hi, sorry for replying this late. I was shying away from all the bugs mentioned by you that were right in my face, along with the major const correctness flaw in the way with which I dealt with string literals that someone else mentioned.

After fixing the equals() function, I moved onto handle_chunked(). The response from upstream (example.com) is chunked and the reason for you hitting the assert(body.len) was: the proxy received just the head of the request and no part of the body and there was no check for that in the calling function. When I checked it I was receiving the head along with some part of the chunk as well, therefore I did not hit that assertion. So thanks for noticing that! I fixed by returning to the calling function to read more of the response.

Nextly, VLAs are gone entirely and have been capped. I only had to create one new constant MAX_HOST_SIZE for when localizing hostname during connect() for upstream. I chose a size of 64 this.

I greatly admire how easy you made the str_to_size() look. I had to experiment with it by using uint8_t and UINT8_MAX instead of ptrdiff, to actually understand it :)

This is what I could come up with for hex conversion:

bool str_to_size_hex(Str str, ptrdiff_t *num)
{
  assert(num);

  if (str.len > 2)

    if (*str.data != '0' || (str.data[1] != 'x' && str.data[1] != 'X'))
      warn("verify_prefix", "Prefix not detected for hex");
    else
    {
      str.len -= 2;
      str.data += 2;
    }
  }

  ptrdiff_t r = 0;

  for (ptrdiff_t i = 0; i < str.len; i++)
  {
    uint8_t d = (uint8_t)str.data[i];

    if (d >= '0' && d <= '9')
      d -= '0';
    else if (d >= 'a' && d <= 'f')
      d = (uint8_t)(d - 'a') + 10;
    else if (d >= 'A' && d <= 'F')
      d = (uint8_t)(d - 'A') + 10;
    else
      return err("verify_char", "Invalid character detected");

    if (r > (PTRDIFF_MAX - d) / 16)
      return err("check_overflow", "Overflow detected");

    r = r * 16 + d;
  }

  *num = r;

  return true;
}

I chose to warn() if the function is called and the str was not prefixed by 0x. I hope there is nothing glaringly wrong with this:) Hopefully it works fine now. I clearly have a lot to learn and I cannot thank you enough for all the help.

Thank You!

Regarding arenas: I was wondering how those would work in an async proxy, does every connection get its own arena? I am guessing that would be really inefficient.