done

Netch/3rd/DnsClient.NET/Protocol/CaaRecord.cs

@@ -0,0 +1,130 @@
+using System;
+namespace DnsClient.Protocol
+{
+    /* RFC 6844 (https://tools.ietf.org/html/rfc6844#section-5.1)
+    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.
+    * */
+
+    /// <summary>
+    /// A <see cref="DnsResourceRecord"/> representing a certification authority authorization.
+    /// <para>
+    /// The Certification Authority Authorization (CAA) DNS Resource Record
+    /// allows a DNS domain name holder to specify one or more Certification
+    /// Authorities(CAs) authorized to issue certificates for that domain.
+    /// </para>
+    /// <para>
+    /// CAA Resource Records allow a public Certification Authority to
+    /// implement additional controls to reduce the risk of unintended
+    /// certificate mis-issue.This document defines the syntax of the CAA
+    /// record and rules for processing CAA records by certificate issuers.
+    /// </para>
+    /// </summary>
+    /// <seealso href="https://tools.ietf.org/html/rfc6844">RFC 6844</seealso>
+    public class CaaRecord : DnsResourceRecord
+    {
+        /// <summary>
+        /// One octet containing the flags.
+        /// </summary>
+        public byte Flags { get; }
+
+        /// <summary>
+        /// The property identifier, a sequence of US-ASCII characters.
+        /// </summary>
+        public string Tag { get; }
+
+        /// <summary>
+        /// A sequence of octets representing the property value.
+        /// Property values are encoded as binary values and MAY employ sub-formats.
+        /// </summary>
+        public string Value { get; }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="CaaRecord"/> class.
+        /// </summary>
+        /// <param name="info">The information.</param>
+        /// <param name="flags">The flags.</param>
+        /// <param name="tag">The tag.</param>
+        /// <param name="value">The value.</param>
+        /// <exception cref="System.ArgumentNullException">If <paramref name="info"/> or <paramref name="tag"/> or <paramref name="value"/> is null.</exception>
+        public CaaRecord(ResourceRecordInfo info, byte flags, string tag, string value) : base(info)
+        {
+            Flags = flags;
+            Tag = tag ?? throw new ArgumentNullException(nameof(tag));
+            Value = value ?? throw new ArgumentNullException(nameof(value));
+        }
+
+        private protected override string RecordToString()
+        {
+            return $"{Flags} {Tag} \"{Value}\"";
+        }
+    }
+}