pub fn read(
decoder: &mut BinDecoder<'_>,
rdata_length: Restrict<u16>
) -> ProtoResult<CAA>Expand description
Read the binary CAA format
RFC 6844, DNS Certification Authority Authorization, January 2013
5.1. Syntax
A CAA RR contains a single property entry consisting of a tag-value
pair. Each tag represents a property of the CAA record. The value
of a CAA property is that specified in the corresponding value field.
A domain name MAY have multiple CAA RRs associated with it and a
given property MAY be specified more than once.
The CAA data field contains one property entry. A property entry
consists of the following data fields:
+0-1-2-3-4-5-6-7-|0-1-2-3-4-5-6-7-|
| Flags | Tag Length = n |
+----------------+----------------+...+---------------+
| Tag char 0 | Tag char 1 |...| Tag char n-1 |
+----------------+----------------+...+---------------+
+----------------+----------------+.....+----------------+
| Value byte 0 | Value byte 1 |.....| Value byte m-1 |
+----------------+----------------+.....+----------------+
Where n is the length specified in the Tag length field and m is the
remaining octets in the Value field (m = d - n - 2) where d is the
length of the RDATA section.
The data fields are defined as follows:
Flags: One octet containing the following fields:
Bit 0, Issuer Critical Flag: If the value is set to '1', the
critical flag is asserted and the property MUST be understood
if the CAA record is to be correctly processed by a certificate
issuer.
A Certification Authority MUST NOT issue certificates for any
Domain that contains a CAA critical property for an unknown or
unsupported property tag that for which the issuer critical
flag is set.
Note that according to the conventions set out in [RFC1035], bit 0
is the Most Significant Bit and bit 7 is the Least Significant
Bit. Thus, the Flags value 1 means that bit 7 is set while a value
of 128 means that bit 0 is set according to this convention.
All other bit positions are reserved for future use.
To ensure compatibility with future extensions to CAA, DNS records
compliant with this version of the CAA specification MUST clear
(set to "0") all reserved flags bits. Applications that interpret
CAA records MUST ignore the value of all reserved flag bits.
Tag Length: A single octet containing an unsigned integer specifying
the tag length in octets. The tag length MUST be at least 1 and
SHOULD be no more than 15.
Tag: The property identifier, a sequence of US-ASCII characters.
Tag values MAY contain US-ASCII characters 'a' through 'z', 'A'
through 'Z', and the numbers 0 through 9. Tag values SHOULD NOT
contain any other characters. Matching of tag values is case
insensitive.
Tag values submitted for registration by IANA MUST NOT contain any
characters other than the (lowercase) US-ASCII characters 'a'
through 'z' and the numbers 0 through 9.
Value: A sequence of octets representing the property value.
Property values are encoded as binary values and MAY employ sub-
formats.
The length of the value field is specified implicitly as the
remaining length of the enclosing Resource Record data field.