feat: implement traversal engine (HAN-380) (#6)

Co-authored-by: Hansen IT Solutions <gary@hansenits.com>
Co-committed-by: Hansen IT Solutions <gary@hansenits.com>

internal/traverse/cache.go

@@ -0,0 +1,124 @@
+package traverse
+
+import (
+	"net"
+	"strings"
+	"sync"
+
+	miekgdns "github.com/miekg/dns"
+)
+
+type InfoCache struct {
+	parent   *InfoCache
+	mu       sync.RWMutex
+	ns       map[string][]string
+	glue     map[string][]net.IP
+}
+
+func NewInfoCache(parent *InfoCache) *InfoCache {
+	return &InfoCache{
+		parent: parent,
+		ns:     make(map[string][]string),
+		glue:   make(map[string][]net.IP),
+	}
+}
+
+func (c *InfoCache) StoreNS(zone string, nameservers []string) {
+	if len(nameservers) == 0 {
+		return
+	}
+	zone = normalize(zone)
+	c.mu.Lock()
+	seen := make(map[string]bool)
+	for _, ns := range nameservers {
+		ns = normalize(ns)
+		if !seen[ns] {
+			seen[ns] = true
+			c.ns[zone] = append(c.ns[zone], ns)
+		}
+	}
+	c.mu.Unlock()
+}
+
+func (c *InfoCache) LookupNS(zone string) []string {
+	zone = normalize(zone)
+	if names := c.localNS(zone); len(names) > 0 {
+		return names
+	}
+	if c.parent != nil {
+		return c.parent.LookupNS(zone)
+	}
+	return nil
+}
+
+func (c *InfoCache) localNS(zone string) []string {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	names, ok := c.ns[zone]
+	if !ok {
+		return nil
+	}
+	result := make([]string, len(names))
+	copy(result, names)
+	return result
+}
+
+func (c *InfoCache) StoreGlue(name string, addrs []net.IP) {
+	if len(addrs) == 0 {
+		return
+	}
+	name = normalize(name)
+	c.mu.Lock()
+	seen := make(map[string]bool)
+	for _, addr := range addrs {
+		key := addr.String()
+		if !seen[key] {
+			seen[key] = true
+			c.glue[name] = append(c.glue[name], addr)
+		}
+	}
+	c.mu.Unlock()
+}
+
+func (c *InfoCache) LookupGlue(name string) []net.IP {
+	name = normalize(name)
+	if addrs := c.localGlue(name); len(addrs) > 0 {
+		return addrs
+	}
+	if c.parent != nil {
+		return c.parent.LookupGlue(name)
+	}
+	return nil
+}
+
+func (c *InfoCache) localGlue(name string) []net.IP {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	addrs, ok := c.glue[name]
+	if !ok {
+		return nil
+	}
+	result := make([]net.IP, len(addrs))
+	copy(result, addrs)
+	return result
+}
+
+func (c *InfoCache) Child() *InfoCache {
+	return NewInfoCache(c)
+}
+
+func (c *InfoCache) NSCount() int {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return len(c.ns)
+}
+
+func (c *InfoCache) GlueCount() int {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return len(c.glue)
+}
+
+func normalize(name string) string {
+	return strings.ToLower(miekgdns.Fqdn(name))
+}