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Fix domain name encoding to Latin1 and canonical case folding to ASCII-only #63

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Fix domain name encoding to Latin1 and canonical case folding to ASCII-only #63

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27 changes: 25 additions & 2 deletions TechnitiumLibrary.Net/Dns/DnsDatagram.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -481,7 +481,7 @@ public static void SerializeDomainName(ReadOnlySpan<char> domain, Stream s, List
domain = domain.Slice(i + 1);
}

if (!Encoding.ASCII.TryGetBytes(label, labelBytes, out labelBytesLength))
if (!Encoding.Latin1.TryGetBytes(label, labelBytes, out labelBytesLength))
throw new DnsClientException("Invalid domain name: label cannot exceed 63 bytes.");

s.WriteByte((byte)labelBytesLength);
Expand Down Expand Up @@ -536,7 +536,7 @@ public static string DeserializeDomainName(Stream s, int maxDepth = 10, bool ign
Span<byte> label = buffer.Slice(0, labelLength);
s.ReadExactly(label);

if (!Encoding.ASCII.TryGetChars(label, domain.Slice(domainPosition), out _))
if (!Encoding.Latin1.TryGetChars(label, domain.Slice(domainPosition), out _))
throw new DnsClientException("Error while reading domain name: domain name length cannot exceed 255 bytes.");

domainPosition += labelLength;
Expand Down Expand Up @@ -566,6 +566,29 @@ public static string DeserializeDomainName(Stream s, int maxDepth = 10, bool ign
return new string(domain.Slice(0, domainPosition));
}

//RFC 4034 section 6.2 canonical form requires lowercasing ASCII A-Z only; every other byte (including
//the Latin-1 supplement range 0xC0-0xDE) must pass through unchanged. string.ToLowerInvariant() does
//full Unicode case folding and would corrupt those bytes, so domain names use this instead wherever
//the result feeds into a signed hash or a canonical-order comparison.
internal static string ToLowerInvariantAscii(string domain)
{
char[] buffer = null;

for (int i = 0; i < domain.Length; i++)
{
char c = domain[i];
if ((c >= 'A') && (c <= 'Z'))
{
if (buffer is null)
buffer = domain.ToCharArray();

buffer[i] = (char)(c + 0x20);
}
}

return buffer is null ? domain : new string(buffer);
}

public static int GetSerializeDomainNameLength(string domain)
{
if (domain.Length == 0)
Expand Down
2 changes: 1 addition & 1 deletion TechnitiumLibrary.Net/Dns/ResourceRecords/CanonicallySerializedResourceRecord.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -56,7 +56,7 @@ public static CanonicallySerializedResourceRecord Create(string name, DnsResourc

//serialize owner name | type | class | Original TTL | RDATA length
buffer.SetLength(0);
DnsDatagram.SerializeDomainName(name.ToLowerInvariant(), buffer);
DnsDatagram.SerializeDomainName(DnsDatagram.ToLowerInvariantAscii(name), buffer);
DnsDatagram.WriteUInt16NetworkOrder((ushort)type, buffer);
DnsDatagram.WriteUInt16NetworkOrder((ushort)@class, buffer);
DnsDatagram.WriteUInt32NetworkOrder(originalTtl, buffer);
Expand Down
6 changes: 3 additions & 3 deletions TechnitiumLibrary.Net/Dns/ResourceRecords/DnsNSECRecordData.cs
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Expand Up @@ -107,8 +107,8 @@ public static bool IsDomainCovered(string ownerName, string nextDomainName, stri

public static int CanonicalComparison(string domain1, string domain2)
{
string[] labels1 = domain1.ToLowerInvariant().Split('.');
string[] labels2 = domain2.ToLowerInvariant().Split('.');
string[] labels1 = DnsDatagram.ToLowerInvariantAscii(domain1).Split('.');
string[] labels2 = DnsDatagram.ToLowerInvariantAscii(domain2).Split('.');

int minLength = labels1.Length;

Expand All @@ -117,7 +117,7 @@ public static int CanonicalComparison(string domain1, string domain2)

for (int i = 0; i < minLength; i++)
{
int value = CanonicalComparison(Encoding.ASCII.GetBytes(labels1[labels1.Length - 1 - i]), Encoding.ASCII.GetBytes(labels2[labels2.Length - 1 - i]));
int value = CanonicalComparison(Encoding.Latin1.GetBytes(labels1[labels1.Length - 1 - i]), Encoding.Latin1.GetBytes(labels2[labels2.Length - 1 - i]));
if (value != 0)
return value;
}
Expand Down