Adds DnsCaaResource.

src/Ae.Dns.Protocol/DnsByteExtensions.cs

@@ -67,15 +67,20 @@ public static ReadOnlyMemory<byte> ReadBytes(ReadOnlyMemory<byte> bytes, int len
             return data;
         }
 
-        private static string ReadStringSimple(ReadOnlyMemory<byte> bytes, ref int offset)
+        private static string ReadStringFromBuffer(ReadOnlySpan<byte> bytes)
         {
-            byte labelLength = bytes.Span[offset];
-            offset += 1;
 #if NETSTANDARD2_0
-            var str = Encoding.ASCII.GetString(bytes.Slice(offset, labelLength).ToArray());
+            return Encoding.ASCII.GetString(bytes.ToArray());
 #else
-            var str = Encoding.ASCII.GetString(bytes.Slice(offset, labelLength).Span);
+            return Encoding.ASCII.GetString(bytes);
 #endif
+        }
+
+        public static string ReadStringWithLengthPrefix(ReadOnlyMemory<byte> bytes, ref int offset)
+        {
+            byte labelLength = bytes.Span[offset];
+            offset += 1;
+            var str = ReadStringFromBuffer(bytes.Slice(offset, labelLength).Span);
             offset += labelLength;
             return str;
         }
@@ -106,7 +111,7 @@ private static List<string> ReadString(ReadOnlyMemory<byte> bytes, ref int offse
                     offset = ReadUInt16(bytes.Span[offset + 1], (byte)(bytes.Span[offset] & (1 << 6) - 1));
                 }
 
-                parts.Add(ReadStringSimple(bytes, ref offset));
+                parts.Add(ReadStringWithLengthPrefix(bytes, ref offset));
             }
 
             if (preCompressionOffset.HasValue)
@@ -171,16 +176,27 @@ public static ArraySegment<byte> Slice(this ArraySegment<byte> buffer, int start
             return reader;
         }
 
-        public static void ToBytes(string value, Memory<byte> buffer, ref int offset)
+        private static int ToBytesNoLengthPrefix(string value, Memory<byte> buffer, ref int offset)
         {
-            // First write the value 1 byte from the offset to leave room for the length byte
 #if NETSTANDARD2_0
             var stringBytes = Encoding.ASCII.GetBytes(value);
-            stringBytes.CopyTo(buffer.Slice(offset + 1, value.Length));
+            stringBytes.CopyTo(buffer.Slice(offset, value.Length));
             var length = stringBytes.Length;
 #else
-            var length = Encoding.ASCII.GetBytes(value, buffer.Slice(offset + 1, value.Length).Span);
+            var length = Encoding.ASCII.GetBytes(value, buffer.Slice(offset, value.Length).Span);
 #endif
+            // Finally advance the offset past the length and value
+            offset += length;
+
+            return length;
+        }
+
+        public static void ToBytes(string value, Memory<byte> buffer, ref int offset)
+        {
+            // First write the value 1 byte from the offset to leave room for the length byte
+            var offsetPlusOne = offset + 1;
+            var length = ToBytesNoLengthPrefix(value, buffer, ref offsetPlusOne);
+
 
             // Then write the length before the value
             buffer.Span[offset] = (byte)length;

src/Ae.Dns.Protocol/Records/DnsCaaResource.cs

@@ -0,0 +1,71 @@
+using System;
+using System.Text;
+
+namespace Ae.Dns.Protocol.Records
+{
+    /// <summary>
+    /// A Certification Authority Authorization (CAA) record is a type of DNS
+    /// resource record that specifies which certificate authorities (CAs) are
+    /// allowed to issue certificates for a domain. The CAA record format is
+    /// specified in RFC 6844.
+    /// </summary>
+    public sealed class DnsCaaResource : IDnsResource, IEquatable<DnsCaaResource>
+    {
+        /// <summary>
+        /// Issuer Critical:  If set to '1', indicates that the corresponding
+        /// property tag MUST be understood if the semantics of the CAA record
+        /// are to be correctly interpreted by an issuer.
+        /// Issuers MUST NOT issue certificates for a domain if the relevant
+        /// CAA Resource Record set contains unknown property tags that have
+        /// the Critical bit set.
+        /// </summary>
+        public byte Flag { get; set; }
+        /// <summary>
+        /// The property identifier, a sequence of US-ASCII characters.
+        /// </summary>
+        public string? Tag { get; set; }
+        /// <summary>
+        /// A sequence of octets representing the property value.
+        /// </summary>
+        public ReadOnlyMemory<byte> Value { get; set; }
+
+        /// <inheritdoc/>
+        public bool Equals(DnsCaaResource? other)
+        {
+            if (other == null)
+            {
+                return false;
+            }
+
+            return Equals(Flag, other.Flag) && Equals(Tag, other.Tag) && Value.Span.SequenceEqual(other.Value.Span);
+        }
+
+        /// <inheritdoc/>
+        public override bool Equals(object? obj) => obj is DnsCaaResource record ? Equals(record) : base.Equals(obj);
+
+        /// <inheritdoc/>
+        public override int GetHashCode() => HashCode.Combine(Flag, Tag, Value);
+
+        /// <inheritdoc/>
+        public void ReadBytes(ReadOnlyMemory<byte> bytes, ref int offset, int length)
+        {
+            var bufferEndPosition = offset + length;
+            Flag = bytes.Span[offset++];
+            Tag = DnsByteExtensions.ReadStringWithLengthPrefix(bytes, ref offset);
+            Value = bytes.Slice(offset, bufferEndPosition - offset);
+            offset = bufferEndPosition;
+        }
+
+        /// <inheritdoc/>
+        public override string ToString() => $"{Flag} {Tag} {Encoding.ASCII.GetString(Value.ToArray())}";
+
+        /// <inheritdoc/>
+        public void WriteBytes(Memory<byte> bytes, ref int offset)
+        {
+            bytes.Span[offset++] = Flag;
+            DnsByteExtensions.ToBytes(Tag ?? string.Empty, bytes, ref offset);
+            Value.CopyTo(bytes.Slice(offset));
+            offset += Value.Length;
+        }
+    }
+}

src/Ae.Dns.Protocol/Records/DnsResourceFactory.cs

@@ -28,6 +28,7 @@ public static IDnsResource CreateResource(DnsQueryType recordType)
                 DnsQueryType.OPT => new DnsOptResource(),
                 DnsQueryType.HTTPS => new DnsServiceBindingResource(),
                 DnsQueryType.SVCB => new DnsServiceBindingResource(),
+                DnsQueryType.CAA => new DnsCaaResource(),
                 _ => new DnsUnknownResource(),
             };
         }