static IReadOnlyList <DnsResourceRecord>?ParseSection(ref DnsParseContext context, int count)
{
if (count == 0)
{
return(null);
}
var result = new DnsResourceRecord[count];
foreach (ref var record in result.AsSpan())
{
string name = context.ReadDomainName();
DnsRecordType qtype = (DnsRecordType)context.ReadUInt16();
DnsEndpointClass qclass = (DnsEndpointClass)context.ReadUInt16();
int ttl = context.ReadInt32();
ushort rdlength = context.ReadUInt16();
record = qtype switch
{
DnsRecordType.A or DnsRecordType.AAAA => new IPRecord(),
DnsRecordType.TXT => new TxtRecord(),
DnsRecordType.CNAME => new DomainNameRecord(),
DnsRecordType.MX => new MXRecord(),
DnsRecordType.SOA => new SoaRecord(),
_ => new UnknownRecord()
};
record.Name = name;
record.Type = qtype;
record.EndpointClass = qclass;
record.AliveSeconds = ttl;
record.ReadData(ref context, rdlength);
}
return(result);
}
var queries = queryCount == 0 ? Array.Empty <DnsQuery>() : new DnsQuery[queryCount];
foreach (ref var query in queries.AsSpan())
{
string name = context.ReadDomainName();
DnsRecordType qtype = (DnsRecordType)context.ReadUInt16();
DnsEndpointClass qclass = (DnsEndpointClass)context.ReadUInt16();
query = new(name, qtype, qclass);
}
message.Queries = queries;
message.Answers = ParseSection(ref context, answerCount);
message.NameServerAuthorities = ParseSection(ref context, serverCount);
message.AdditionalRecords = ParseSection(ref context, additionalCount);
bytesConsumed = context.BytesConsumed;
return(message);
}
public static DnsMessage ParseMessage(ReadOnlySpan <byte> span, out int bytesConsumed)
{
var context = new DnsParseContext(span);
var message = new DnsMessage
{
QueryId = context.ReadUInt16(),
};
ushort flags = context.ReadUInt16();
int queryCount = context.ReadUInt16();
int answerCount = context.ReadUInt16();
int serverCount = context.ReadUInt16();
int additionalCount = context.ReadUInt16();
message.IsResponse = (flags & ResponseFlag) != 0;
message.Operation = (DnsOperation)((flags & OpCodeMask) >> OpCodeShift);
message.IsAuthoritativeAnswer = (flags & AuthoritativeMask) != 0;
message.IsTruncated = (flags & TruncationMask) != 0;
message.IsRecursionDesired = (flags & RecursionDesiredMask) != 0;
message.IsRecursionAvailable = (flags & RecursionAvailableMask) != 0;
message.ResponseCode = (DnsResponseCode)(flags & ResponseCodeMask);