Initial commit

checker/collect.go

@@ -0,0 +1,474 @@
+package checker
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"strings"
+	"sync"
+
+	"github.com/miekg/dns"
+
+	sdk "git.happydns.org/checker-sdk-go/checker"
+)
+
+// Collect runs the alias observation and returns an *AliasData populated with
+// raw facts: the resolution chain, apex/DNSSEC flags, coexisting RRsets, and
+// chain-termination reason. It does not judge; judgement lives in the rules.
+func (p *aliasProvider) Collect(ctx context.Context, opts sdk.CheckerOptions) (any, error) {
+	owner, err := resolveOwner(opts)
+	if err != nil {
+		return nil, err
+	}
+
+	maxChain := sdk.GetIntOption(opts, "maxChainLength", 8)
+	requireTarget := sdk.GetBoolOption(opts, "requireResolvableTarget", true)
+	_ = requireTarget // Consumed by target_resolvable rule, not collection.
+
+	data := &AliasData{Owner: owner}
+
+	resolver := systemResolver()
+
+	// 1. Find apex and authoritative servers.
+	apex, servers, err := findApex(ctx, owner, resolver)
+	if err != nil {
+		data.ApexLookupError = err.Error()
+		return data, nil
+	}
+	data.Apex = apex
+	data.AuthServers = servers
+	data.OwnerIsApex = lowerFQDN(owner) == lowerFQDN(apex)
+
+	// 2. Detect DNAME substitutions from owner up to apex (exclusive of apex).
+	data.DNAMESubstitutions = collectDNAMEs(ctx, servers, owner, apex)
+
+	// 3. Walk the CNAME/DNAME chain.
+	chainCtx := &chainCtx{
+		data:        data,
+		maxLen:      maxChain,
+		servers:     servers,
+		apex:        apex,
+		seenOwners:  map[string]bool{},
+		recFallback: resolver,
+	}
+	chainCtx.walk(ctx, owner)
+
+	// 4. Apex-level observations (flattening, CNAME-at-apex).
+	if data.OwnerIsApex {
+		observeApex(ctx, data, servers, apex)
+	}
+
+	// 5. Coexistence at owner (applies at any level, not just apex).
+	observeCoexistence(ctx, data, servers, owner)
+
+	// 6. DNSSEC observations.
+	observeDNSSEC(ctx, data, servers, apex, owner)
+
+	return data, nil
+}
+
+// resolveOwner derives the FQDN to check from the auto-filled options. The
+// "service" option takes precedence (it carries a dns.CNAME whose owner is
+// authoritative); otherwise we fall back to subdomain + domain_name.
+func resolveOwner(opts sdk.CheckerOptions) (string, error) {
+	if svcMsg, ok := sdk.GetOption[serviceMessage](opts, "service"); ok && len(svcMsg.Service) > 0 {
+		var c cnameService
+		if err := json.Unmarshal(svcMsg.Service, &c); err == nil && c.Record != nil && c.Record.Hdr.Name != "" {
+			return lowerFQDN(c.Record.Hdr.Name), nil
+		}
+	}
+
+	parent, _ := sdk.GetOption[string](opts, "domain_name")
+	sub, _ := sdk.GetOption[string](opts, "subdomain")
+	if parent == "" {
+		return "", fmt.Errorf("missing 'domain_name' option")
+	}
+	parent = strings.TrimSuffix(parent, ".")
+	if sub == "" || sub == "@" {
+		return lowerFQDN(parent), nil
+	}
+	sub = strings.TrimSuffix(sub, ".")
+	return lowerFQDN(sub + "." + parent), nil
+}
+
+// chainCtx carries the mutable state of a chain walk.
+type chainCtx struct {
+	data        *AliasData
+	maxLen      int
+	servers     []string
+	apex        string
+	seenOwners  map[string]bool
+	recFallback string
+}
+
+// walk follows CNAME/DNAME hops starting from name. It writes hops into
+// data.Chain and records the termination reason in data.ChainTerminated.
+func (c *chainCtx) walk(ctx context.Context, name string) {
+	current := lowerFQDN(name)
+	currentServers := c.servers
+
+	for i := 0; i <= c.maxLen+1; i++ {
+		if c.seenOwners[current] {
+			c.data.ChainTerminated = ChainTermination{
+				Reason:  TermLoop,
+				Subject: current,
+				Detail:  fmt.Sprintf("chain loops back to %s", current),
+			}
+			c.data.FinalTarget = current
+			return
+		}
+		c.seenOwners[current] = true
+
+		if i > c.maxLen {
+			c.data.ChainTerminated = ChainTermination{
+				Reason:  TermTooLong,
+				Subject: current,
+				Detail:  fmt.Sprintf("chain exceeds %d hops at %s", c.maxLen, current),
+			}
+			c.data.FinalTarget = current
+			return
+		}
+
+		q := dns.Question{Name: current, Qtype: dns.TypeCNAME, Qclass: dns.ClassINET}
+		r, server, err := c.queryFor(ctx, currentServers, q)
+		if err != nil {
+			c.data.ChainTerminated = ChainTermination{
+				Reason:  TermQueryErr,
+				Subject: current,
+				Detail:  err.Error(),
+			}
+			c.data.FinalTarget = current
+			return
+		}
+
+		if r.Rcode != dns.RcodeSuccess {
+			rcode := rcodeText(r.Rcode)
+			c.data.ChainTerminated = ChainTermination{
+				Reason:  TermRcode,
+				Subject: current,
+				Rcode:   rcode,
+				Detail:  fmt.Sprintf("server answered %s for %s", rcode, current),
+			}
+			c.data.FinalTarget = current
+			return
+		}
+
+		cname, synthesizedFromDNAME, ttl := extractCNAME(r, current)
+		if cname == "" {
+			// No CNAME at this name: terminal hop, resolve A/AAAA.
+			c.data.Chain = append(c.data.Chain, ChainHop{
+				Owner:  current,
+				Kind:   KindTarget,
+				Server: server,
+			})
+			c.data.FinalTarget = current
+			c.data.ChainTerminated = ChainTermination{Reason: TermOK}
+			c.resolveFinal(ctx, current, currentServers)
+			return
+		}
+
+		if current == c.data.Owner && !synthesizedFromDNAME {
+			c.data.OwnerHasCNAME = true
+		}
+
+		target := lowerFQDN(cname)
+		kind := KindCNAME
+		if synthesizedFromDNAME {
+			kind = KindDNAME
+		}
+		c.data.Chain = append(c.data.Chain, ChainHop{
+			Owner:       current,
+			Kind:        kind,
+			Target:      target,
+			TTL:         ttl,
+			Server:      server,
+			Synthesized: synthesizedFromDNAME,
+		})
+
+		// Re-evaluate servers for the next hop: if target leaves the apex,
+		// we need its own authoritative servers. Out-of-zone targets are
+		// resolved via the system resolver (recursive path).
+		if isSubdomain(target, c.apex) {
+			currentServers = c.servers
+		} else {
+			zone, _, _ := findApex(ctx, target, c.recFallback)
+			ns, err := resolveZoneNSAddrs(ctx, zone)
+			if err != nil || len(ns) == 0 {
+				currentServers = []string{c.recFallback}
+			} else {
+				currentServers = ns
+			}
+		}
+		current = target
+	}
+}
+
+// queryFor sends q, retrying via the recursive resolver if the authoritative
+// set is empty (useful for foreign targets).
+func (c *chainCtx) queryFor(ctx context.Context, servers []string, q dns.Question) (*dns.Msg, string, error) {
+	if len(servers) == 0 {
+		r, err := recursiveExchange(ctx, c.recFallback, q)
+		return r, c.recFallback, err
+	}
+	return queryAtAuth(ctx, "", servers, q)
+}
+
+// extractCNAME returns the first CNAME target matched for owner, and reports
+// whether it was synthesized from a DNAME present in the same response.
+func extractCNAME(r *dns.Msg, owner string) (target string, fromDNAME bool, ttl uint32) {
+	for _, rr := range r.Answer {
+		if c, ok := rr.(*dns.CNAME); ok && strings.EqualFold(dns.Fqdn(c.Hdr.Name), dns.Fqdn(owner)) {
+			target = c.Target
+			ttl = c.Hdr.Ttl
+			break
+		}
+	}
+	if target == "" {
+		return "", false, 0
+	}
+	for _, rr := range r.Answer {
+		if _, ok := rr.(*dns.DNAME); ok {
+			fromDNAME = true
+			break
+		}
+	}
+	return
+}
+
+// resolveFinal fetches A/AAAA of the final target and records them.
+func (c *chainCtx) resolveFinal(ctx context.Context, name string, servers []string) {
+	var wg sync.WaitGroup
+	var finalA, finalAAAA []string
+	var rcode string
+
+	wg.Add(2)
+	go func() {
+		defer wg.Done()
+		q := dns.Question{Name: dns.Fqdn(name), Qtype: dns.TypeA, Qclass: dns.ClassINET}
+		var r *dns.Msg
+		var err error
+		if len(servers) > 0 {
+			r, _, err = queryAtAuth(ctx, "", servers, q)
+		} else {
+			r, err = recursiveExchange(ctx, c.recFallback, q)
+		}
+		if err == nil && r != nil {
+			if r.Rcode != dns.RcodeSuccess {
+				rcode = rcodeText(r.Rcode)
+			}
+			for _, rr := range r.Answer {
+				if a, ok := rr.(*dns.A); ok {
+					finalA = append(finalA, a.A.String())
+				}
+			}
+		}
+	}()
+	go func() {
+		defer wg.Done()
+		q := dns.Question{Name: dns.Fqdn(name), Qtype: dns.TypeAAAA, Qclass: dns.ClassINET}
+		var r *dns.Msg
+		var err error
+		if len(servers) > 0 {
+			r, _, err = queryAtAuth(ctx, "", servers, q)
+		} else {
+			r, err = recursiveExchange(ctx, c.recFallback, q)
+		}
+		if err == nil && r != nil {
+			for _, rr := range r.Answer {
+				if aaaa, ok := rr.(*dns.AAAA); ok {
+					finalAAAA = append(finalAAAA, aaaa.AAAA.String())
+				}
+			}
+		}
+	}()
+	wg.Wait()
+
+	c.data.FinalA = append(c.data.FinalA, finalA...)
+	c.data.FinalAAAA = append(c.data.FinalAAAA, finalAAAA...)
+	if rcode != "" {
+		c.data.FinalRcode = rcode
+	}
+}
+
+// collectDNAMEs queries every label from owner up to (but excluding) apex for
+// a DNAME record, returning any substitutions found.
+func collectDNAMEs(ctx context.Context, servers []string, owner, apex string) []ChainHop {
+	labels := dns.SplitDomainName(owner)
+	apexLabels := dns.SplitDomainName(apex)
+	stop := max(len(labels)-len(apexLabels), 0)
+
+	results := make([][]ChainHop, stop)
+	var wg sync.WaitGroup
+	wg.Add(stop)
+	for i := range stop {
+		go func() {
+			defer wg.Done()
+			name := dns.Fqdn(strings.Join(labels[i:], "."))
+			q := dns.Question{Name: name, Qtype: dns.TypeDNAME, Qclass: dns.ClassINET}
+			r, server, err := queryAtAuth(ctx, "", servers, q)
+			if err != nil || r == nil || r.Rcode != dns.RcodeSuccess {
+				return
+			}
+			for _, rr := range r.Answer {
+				if d, ok := rr.(*dns.DNAME); ok {
+					results[i] = append(results[i], ChainHop{
+						Owner:  lowerFQDN(d.Hdr.Name),
+						Kind:   KindDNAME,
+						Target: lowerFQDN(d.Target),
+						TTL:    d.Hdr.Ttl,
+						Server: server,
+					})
+				}
+			}
+		}()
+	}
+	wg.Wait()
+
+	var out []ChainHop
+	for _, hops := range results {
+		out = append(out, hops...)
+	}
+	return out
+}
+
+// observeApex records apex-level signals: A/AAAA presence, CNAME-at-apex,
+// ALIAS/ANAME flattening.
+func observeApex(ctx context.Context, data *AliasData, servers []string, apex string) {
+	var hasA, hasAAAA bool
+	var wg sync.WaitGroup
+	wg.Add(2)
+	go func() {
+		defer wg.Done()
+		q := dns.Question{Name: apex, Qtype: dns.TypeA, Qclass: dns.ClassINET}
+		r, _, err := queryAtAuth(ctx, "", servers, q)
+		if err != nil || r == nil {
+			return
+		}
+		for _, rr := range r.Answer {
+			if _, ok := rr.(*dns.A); ok {
+				hasA = true
+				return
+			}
+		}
+	}()
+	go func() {
+		defer wg.Done()
+		q := dns.Question{Name: apex, Qtype: dns.TypeAAAA, Qclass: dns.ClassINET}
+		r, _, err := queryAtAuth(ctx, "", servers, q)
+		if err != nil || r == nil {
+			return
+		}
+		for _, rr := range r.Answer {
+			if _, ok := rr.(*dns.AAAA); ok {
+				hasAAAA = true
+				return
+			}
+		}
+	}()
+	wg.Wait()
+
+	data.ApexHasA = hasA
+	data.ApexHasAAAA = hasAAAA
+
+	for _, h := range data.Chain {
+		if h.Kind == KindCNAME && h.Owner == lowerFQDN(apex) {
+			data.ApexHasCNAME = true
+			break
+		}
+	}
+
+	if (hasA || hasAAAA) && !data.ApexHasCNAME {
+		data.ApexFlattening = true
+	}
+}
+
+// observeCoexistence records any sibling RRsets that sit next to a CNAME at
+// the owner.
+func observeCoexistence(ctx context.Context, data *AliasData, servers []string, owner string) {
+	if !data.OwnerHasCNAME {
+		return
+	}
+
+	siblings := []uint16{
+		dns.TypeA, dns.TypeAAAA, dns.TypeMX, dns.TypeTXT,
+		dns.TypeNS, dns.TypeSRV, dns.TypeCAA,
+	}
+	seen := map[string]uint32{}
+	var mu sync.Mutex
+	var wg sync.WaitGroup
+	wg.Add(len(siblings))
+	for _, qt := range siblings {
+		go func() {
+			defer wg.Done()
+			q := dns.Question{Name: owner, Qtype: qt, Qclass: dns.ClassINET}
+			r, _, err := queryAtAuth(ctx, "", servers, q)
+			if err != nil || r == nil {
+				return
+			}
+			// A synthesized CNAME from DNAME will be present in Answer for
+			// any type; only count answers whose owner matches and whose
+			// type is qt.
+			for _, rr := range r.Answer {
+				if rr.Header().Rrtype != qt {
+					continue
+				}
+				if !strings.EqualFold(dns.Fqdn(rr.Header().Name), dns.Fqdn(owner)) {
+					continue
+				}
+				mu.Lock()
+				seen[dns.TypeToString[qt]] = rr.Header().Ttl
+				mu.Unlock()
+				break
+			}
+		}()
+	}
+	wg.Wait()
+
+	for t, ttl := range seen {
+		data.Coexisting = append(data.Coexisting, CoexistingRRset{Type: t, TTL: ttl})
+	}
+}
+
+// observeDNSSEC records whether the apex zone is signed and, when a CNAME is
+// present at owner, whether it carries an RRSIG.
+func observeDNSSEC(ctx context.Context, data *AliasData, servers []string, apex, owner string) {
+	qk := dns.Question{Name: apex, Qtype: dns.TypeDNSKEY, Qclass: dns.ClassINET}
+	r, _, err := queryAtAuth(ctx, "tcp", servers, qk)
+	if err != nil || r == nil || r.Rcode != dns.RcodeSuccess {
+		return
+	}
+	signed := false
+	for _, rr := range r.Answer {
+		if _, ok := rr.(*dns.DNSKEY); ok {
+			signed = true
+			break
+		}
+	}
+	data.ZoneSigned = signed
+	if !signed {
+		return
+	}
+
+	// Query CNAME with DO; check for an RRSIG covering it.
+	q := dns.Question{Name: owner, Qtype: dns.TypeCNAME, Qclass: dns.ClassINET}
+	r, _, err = queryAtAuth(ctx, "tcp", servers, q)
+	if err != nil || r == nil {
+		return
+	}
+	sawCNAME := false
+	sawSig := false
+	for _, rr := range r.Answer {
+		switch v := rr.(type) {
+		case *dns.CNAME:
+			sawCNAME = true
+		case *dns.RRSIG:
+			if v.TypeCovered == dns.TypeCNAME {
+				sawSig = true
+			}
+		}
+	}
+	if sawCNAME {
+		data.CNAMESigCheckDone = true
+		data.CNAMESigned = sawSig
+	}
+}