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chore: add TypeTSIG/RcodeMask constants, remove dead code, refactor FORMERR builder #7

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Merged
PhantomInTheWire merged 1 commit into from
Feb 25, 2026
Merged

chore: add TypeTSIG/RcodeMask constants, remove dead code, refactor FORMERR builder #7

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12 changes: 7 additions & 5 deletions internal/dns/message.go
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Original file line number Diff line number Diff line change
Expand Up @@ -35,10 +35,11 @@ const (
FlagRD = 0x0100 // Bit 8: Recursion Desired
FlagRA = 0x0080 // Bit 7: Recursion Available

RcodeSuccess = 0 // No error
RcodeFormat = 1 // Format error - request malformed
RcodeServer = 2 // Server failure
RcodeNXDomain = 3 // Non-existent domain
RcodeSuccess = 0 // No error
RcodeFormat = 1 // Format error - request malformed
RcodeServer = 2 // Server failure
RcodeNXDomain = 3 // Non-existent domain
RcodeMask = 0x000F // Bottom 4 bits: Response code

TypeA uint16 = 1
TypeNS uint16 = 2
Expand All @@ -48,6 +49,7 @@ const (
TypeTXT uint16 = 16
TypeAAAA uint16 = 28
TypeOPT uint16 = 41
TypeTSIG uint16 = 250
ClassIN uint16 = 1

MaxMessageSize = 4096
Expand Down Expand Up @@ -337,7 +339,7 @@ func ValidateResponseWithRequest(reqHeader Header, reqQuestions []Question, resp
return ErrIDMismatch
}

if respHeader.Flags&0x8000 == 0 {
if respHeader.Flags&FlagQR == 0 {
return ErrNotResponse
}

Expand Down
2 changes: 1 addition & 1 deletion internal/dns/response.go
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Original file line number Diff line number Diff line change
Expand Up @@ -80,7 +80,7 @@ func BuildResponse(req []byte, answers []Answer, rcode uint16) ([]byte, error) {
}

func responseFlags(reqFlags uint16, rcode uint16) uint16 {
return FlagQR | (reqFlags & FlagOpcode) | (reqFlags & FlagRD) | FlagRA | (rcode & 0x000F)
return FlagQR | (reqFlags & FlagOpcode) | (reqFlags & FlagRD) | FlagRA | (rcode & RcodeMask)
}

// MinimizeResponse strips authority/additional sections to reduce size.
Expand Down
58 changes: 1 addition & 57 deletions internal/dns/ttl.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,62 +2,6 @@ package dns

import "encoding/binary"

// RewriteAllRRsTTL rewrites the TTL field for all resource records
// (answer/authority/additional) to the provided value.
// This is used to serve cached packets with a TTL reflecting remaining lifetime.
//
// OPT (EDNS0) and TSIG are pseudo-RRs; their "TTL" fields are not TTLs and must not be rewritten.
func RewriteAllRRsTTL(msg []byte, ttl uint32) error {
h, err := ReadHeader(msg)
if err != nil {
return err
}
off := HeaderLen
for i := 0; i < int(h.QDCount); i++ {
next, err := SkipName(msg, off)
if err != nil {
return err
}
if len(msg) < next+4 {
return ErrShortBuffer
}
off = next + 4 // QTYPE(2) + QCLASS(2)
}

rewriteRR := func(count uint16) error {
for i := 0; i < int(count); i++ {
next, err := SkipName(msg, off)
if err != nil {
return err
}
if len(msg) < next+10 {
return ErrShortBuffer
}
rrType := binary.BigEndian.Uint16(msg[next : next+2])
if rrType != TypeOPT && rrType != 250 {
binary.BigEndian.PutUint32(msg[next+4:next+8], ttl)
}
rdlen := int(binary.BigEndian.Uint16(msg[next+8 : next+10]))
off = next + 10 + rdlen
if off > len(msg) {
return ErrShortBuffer
}
}
return nil
}

if err := rewriteRR(h.ANCount); err != nil {
return err
}
if err := rewriteRR(h.NSCount); err != nil {
return err
}
if err := rewriteRR(h.ARCount); err != nil {
return err
}
return nil
}

// RewriteTTLsAtOffsets rewrites TTL fields at provided offsets.
// Offsets must point at the start of the 4-byte TTL field.
func RewriteTTLsAtOffsets(msg []byte, ttl uint32, offsets []uint16) {
Expand Down Expand Up @@ -103,7 +47,7 @@ func CollectTTLOffsets(msg []byte) ([]uint16, error) {
return ErrShortBuffer
}
rrType := binary.BigEndian.Uint16(msg[next : next+2])
if rrType != TypeOPT && rrType != 250 {
if rrType != TypeOPT && rrType != TypeTSIG {
ttlOff := next + 4
if ttlOff+4 <= len(msg) {
offsets = append(offsets, uint16(ttlOff))
Expand Down
48 changes: 0 additions & 48 deletions internal/dns/util.go
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Original file line number Diff line number Diff line change
Expand Up @@ -11,41 +11,6 @@ func NormalizeName(name string) string {
return asciiLowerIfNeeded(name)
}

// JoinLabels joins a slice of domain name labels with dots.
// Returns "." if the labels slice is empty.
func JoinLabels(labels []string) string {
if len(labels) == 0 {
return "."
}
return strings.Join(labels, ".")
}

// SplitLabels splits a domain name into its constituent labels.
// Returns an empty slice for empty names or root (".") names.
func SplitLabels(name string) []string {
if name == "" || name == "." {
return nil
}
name = strings.TrimSuffix(name, ".")

dotCount := strings.Count(name, ".")
labels := make([]string, 0, dotCount+1)

start := 0
for i := 0; i < len(name); i++ {
if name[i] == '.' {
if i > start {
labels = append(labels, name[start:i])
}
start = i + 1
}
}
if start < len(name) {
labels = append(labels, name[start:])
}
return labels
}

// IsSubdomain checks if child is a subdomain of parent.
// Both names should be normalized (lowercase, no trailing dot).
func IsSubdomain(child, parent string) bool {
Expand Down Expand Up @@ -161,16 +126,3 @@ func BuildQueryIntoWithEDNS(buf []byte, id uint16, name string, qtype, qclass ui

return off, nil
}

// BuildQuery constructs a DNS query message for the given name, type, and class.
// It uses a maximum-size buffer to avoid calculation errors, as DNS messages
// over UDP are limited to 512 bytes per RFC 1035.
// Returns the serialized query as a byte slice.
func BuildQuery(id uint16, name string, qtype, qclass uint16) ([]byte, error) {
buf := make([]byte, MaxMessageSize)
n, err := BuildQueryInto(buf, id, name, qtype, qclass)
if err != nil {
return nil, err
}
return buf[:n], nil
}
4 changes: 2 additions & 2 deletions internal/resolver/recursive.go
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Original file line number Diff line number Diff line change
Expand Up @@ -457,7 +457,7 @@ func (r *Recursive) resolveIterative(ctx context.Context, reqHeader dns.Header,
}

if debugEnabled {
rcode := respMsg.Header.Flags & 0x000F
rcode := respMsg.Header.Flags & dns.RcodeMask
kind := "empty"
if len(respMsg.Answers) > 0 {
kind = "answer"
Expand Down Expand Up @@ -506,7 +506,7 @@ func (r *Recursive) resolveIterative(ctx context.Context, reqHeader dns.Header,
return minimized, cleanup, nil
}

if (respMsg.Header.Flags & 0x000F) == dns.RcodeNXDomain {
if (respMsg.Header.Flags & dns.RcodeMask) == dns.RcodeNXDomain {
respMsg.Release()
segMin := r.tracers.iterMinimize.TraceNested(sampled)
minimized, _ := minimizeAndSetID(resp, clientID, true)
Expand Down
4 changes: 2 additions & 2 deletions internal/resolver/utils.go
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Original file line number Diff line number Diff line change
Expand Up @@ -97,7 +97,7 @@ func servfailFromRequest(req []byte) ([]byte, bool) {
resp := make([]byte, qEnd)
copy(resp, req[:qEnd])

hdr.Flags = dns.FlagQR | (hdr.Flags & dns.FlagOpcode) | (hdr.Flags & dns.FlagRD) | dns.FlagRA | (dns.RcodeServer & 0x000F)
hdr.Flags = dns.FlagQR | (hdr.Flags & dns.FlagOpcode) | (hdr.Flags & dns.FlagRD) | dns.FlagRA | (dns.RcodeServer & dns.RcodeMask)
hdr.QDCount = 1
hdr.ANCount = 0
hdr.NSCount = 0
Expand Down Expand Up @@ -134,7 +134,7 @@ func sleepOrDone(ctx context.Context, d time.Duration) bool {
// - NXDOMAIN and NOERROR/NODATA negative caching using SOA.MINIMUM (RFC2308-ish).
// It returns (ttl, true) when cacheable.
func cacheTTLForResponse(fullResp []byte, msg dns.Message, q dns.Question) (time.Duration, bool) {
rcode := msg.Header.Flags & 0x000F
rcode := msg.Header.Flags & dns.RcodeMask
q = q.Normalize()

soaTTL, hasSOA := negativeTTLFromSOA(fullResp, msg.Authorities)
Expand Down
24 changes: 5 additions & 19 deletions internal/server/udp.go
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Original file line number Diff line number Diff line change
Expand Up @@ -23,7 +23,7 @@ func (s *Server) maybeLogServfail(resp []byte, addr net.Addr) {
if err != nil {
return
}
if (hdr.Flags & 0x000F) != dns.RcodeServer {
if (hdr.Flags & dns.RcodeMask) != dns.RcodeServer {
return
}
s.logger.Debug("sending SERVFAIL", "id", hdr.ID, "bytes", len(resp), "addr", addr.String())
Expand Down Expand Up @@ -146,25 +146,11 @@ func (s *Server) udpReadLoop(ctx context.Context, writer *udpWriter, cacheResolv
if !dns.IsValidRequest(b[:n]) {
if hdr, err := dns.ReadHeader(b[:n]); err == nil {
var formerr [dns.HeaderLen]byte
formerr[0] = byte(hdr.ID >> 8)
formerr[1] = byte(hdr.ID)
// 0x80 = QR=1 (response), 0x01 = RD; preserve OPCODE from request
opcode := byte((hdr.Flags & dns.FlagOpcode) >> 8)
if hdr.Flags&dns.FlagRD != 0 {
formerr[2] = 0x80 | 0x01 | opcode
} else {
formerr[2] = 0x80 | opcode
fmtHdr := dns.Header{
ID: hdr.ID,
Flags: dns.FlagQR | (hdr.Flags & dns.FlagOpcode) | (hdr.Flags & dns.FlagRD) | (dns.RcodeFormat & dns.RcodeMask),
}
// RCODE=1 (Format Error)
formerr[3] = 0x01
formerr[4] = 0x00
formerr[5] = 0x00
formerr[6] = 0x00
formerr[7] = 0x00
formerr[8] = 0x00
formerr[9] = 0x00
formerr[10] = 0x00
formerr[11] = 0x00
_ = dns.WriteHeader(formerr[:], fmtHdr)
if _, err := writer.conn.WriteTo(formerr[:], addr); err != nil {
s.WriteErrors.Add(1)
}
Expand Down
2 changes: 1 addition & 1 deletion internal/server/utils.go
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Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,7 @@ func servfailFromRequestInPlace(req []byte) ([]byte, bool) {
return nil, false
}

hdr.Flags = dns.FlagQR | (hdr.Flags & dns.FlagOpcode) | (hdr.Flags & dns.FlagRD) | dns.FlagRA | (dns.RcodeServer & 0x000F)
hdr.Flags = dns.FlagQR | (hdr.Flags & dns.FlagOpcode) | (hdr.Flags & dns.FlagRD) | dns.FlagRA | (dns.RcodeServer & dns.RcodeMask)
hdr.QDCount = 1
hdr.ANCount = 0
hdr.NSCount = 0
Expand Down