Phase 4.1: Error handling, edge cases, and robustness (#11)

internal/traverse/traverser.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net"
 	"sync"
+	"time"
 
 	"github.com/hits/ExploreDNS/internal/dns"
 	miekgdns "github.com/miekg/dns"
@@ -17,6 +18,12 @@ type TraverserConfig struct {
 	QueryConfig *dns.QueryConfig
 	RootAddrs   []net.IP
 	Hooks       *TraverserHooks
+	// Fast controls cache sharing across branches. When true (default), child
+	// branches inherit glue discovered by earlier branches via the shared root
+	// cache, trading accuracy for speed. When false, each branch gets a
+	// completely independent cache — slower but results are not contaminated by
+	// sibling branch observations.
+	Fast bool
 }
 
 func DefaultTraverserConfig() *TraverserConfig {
@@ -26,6 +33,7 @@ func DefaultTraverserConfig() *TraverserConfig {
 		RootConfig:  nil,
 		QueryConfig: nil,
 		RootAddrs:   nil,
+		Fast:        true,
 	}
 }
 
@@ -97,9 +105,19 @@ func (t *Traverser) Traverse(ctx context.Context, name string) ([]TraversalResul
 			break
 		}
 
-		cache := rootCache
-		if ref.Parent != nil {
-			cache = rootCache.Child()
+		var cache *InfoCache
+		if t.config.Fast {
+			// Fast mode: inherit glue from the shared root cache so earlier
+			// branch discoveries are visible to later branches.
+			cache = rootCache
+			if ref.Parent != nil {
+				cache = rootCache.Child()
+			}
+		} else {
+			// Non-fast mode: every referral gets its own independent cache so
+			// no cross-branch glue is reused, ensuring each path is resolved
+			// from scratch.
+			cache = NewInfoCache(nil)
 		}
 
 		if t.config.Hooks != nil {
@@ -141,7 +159,19 @@ func (t *Traverser) Traverse(ctx context.Context, name string) ([]TraversalResul
 		if resp.Type == RespCNAMEFollow {
 			follow := resp.CNAMEFollowReferral()
 			if follow != nil {
-				if !stack.Push(follow) {
+				// Detect CNAME loop: target name already appears in the ancestor chain.
+				if follow.Parent != nil && follow.Parent.IsNameInChain(follow.Name) {
+					mu.Lock()
+					results = append(results, TraversalResult{
+						Referral: follow,
+						Response: &Response{
+							Referral:     follow,
+							Type:         RespCNAMELoop,
+							ErrorMessage: fmt.Sprintf("CNAME loop detected: %s already in traversal chain", follow.Name),
+						},
+					})
+					mu.Unlock()
+				} else if !stack.Push(follow) {
 					mu.Lock()
 					results = append(results, TraversalResult{
 						Referral: follow,
@@ -412,12 +442,16 @@ func (t *Traverser) resolveGlueViaSystem(ctx context.Context, name string, cache
 
 	c := &miekgdns.Client{
 		Net:          "udp",
-		ReadTimeout:  5,
-		WriteTimeout: 5,
+		ReadTimeout:  5 * time.Second,
+		WriteTimeout: 5 * time.Second,
 	}
 	if deadline, ok := ctx.Deadline(); ok {
-		c.ReadTimeout = deadline.Sub(deadline)
-		c.WriteTimeout = deadline.Sub(deadline)
+		remaining := time.Until(deadline)
+		if remaining <= 0 {
+			return nil
+		}
+		c.ReadTimeout = remaining
+		c.WriteTimeout = remaining
 	}
 
 	fqdn := miekgdns.Fqdn(name)