[DxeNetLib] Why do we restrict each field to have the same leading zero format?

[Guoheyi <guoheyi@huawei.com>]

Hi folks,

We are using NetLibAsciiStrToIp6 function in DxeNetLib.c of MdeModulePkg to convert string to IPv6 address. We found this function will return invalid parameter with below input:
2001:3456:789a:0000:f012:2:2003:2005

We trace the code and believe it is handled by the branch in line 2955:

      if ((Cnt != 0) && (Cnt < 4) && LeadZero) {
        return EFI_INVALID_PARAMETER;
      }

I think the reason is that we have field 3 of "0000" which has leading zero and causes LeadZero flag to be true, and it requires all the following fields to have the same leading zero format, while field 5 of "2" is not.

I checked RFC 4291 and only found below text; I didn't find any restriction that requires each field to have the same leading zero format.

   1. The preferred form is x:x:x:x:x:x:x:x, where the 'x's are one to
      four hexadecimal digits of the eight 16-bit pieces of the address.
      Examples:

         ABCD:EF01:2345:6789:ABCD:EF01:2345:6789

         2001:DB8:0:0:8:800:200C:417A

      Note that it is not necessary to write the leading zeros in an
      individual field, but there must be at least one numeral in every
      field (except for the case described in 2.).

Could you help to confirm whether it is a bug or there is some special reason for this?

Thanks and regards,

Gary (Heyi Guo)