fix: only set gotTimeout for actual timeout errors

Previously, querySingleType set gotTimeout=true for any queryDNS error,
misclassifying connection refused, network unreachable, etc. as timeouts.

Now uses errors.As(err, &net.Error) with Timeout() check to distinguish
real timeouts from other network errors. Non-timeout errors are tracked
via a new gotError field and classified as StatusError.

internal/resolver/errors.go

@@ -4,11 +4,6 @@ import "errors"
 
 // Sentinel errors returned by the resolver.
 var (
-	// ErrNotImplemented indicates a method is stubbed out.
-	ErrNotImplemented = errors.New(
-		"resolver not yet implemented",
-	)
-
 	// ErrNoNameservers is returned when no authoritative NS
 	// could be discovered for a domain.
 	ErrNoNameservers = errors.New(

internal/resolver/iterative.go

@@ -435,6 +435,23 @@ func (r *Resolver) QueryNameserver(
 	return r.queryAllTypes(ctx, nsHostname, nsIPs[0], hostname)
 }
 
+// QueryNameserverIP queries a nameserver by its IP address directly,
+// bypassing NS hostname resolution.
+func (r *Resolver) QueryNameserverIP(
+	ctx context.Context,
+	nsHostname string,
+	nsIP string,
+	hostname string,
+) (*NameserverResponse, error) {
+	if checkCtx(ctx) != nil {
+		return nil, ErrContextCanceled
+	}
+
+	hostname = dns.Fqdn(hostname)
+
+	return r.queryAllTypes(ctx, nsHostname, nsIP, hostname)
+}
+
 func (r *Resolver) queryAllTypes(
 	ctx context.Context,
 	nsHostname string,
@@ -462,6 +479,8 @@ func (r *Resolver) queryAllTypes(
 type queryState struct {
 	gotNXDomain bool
 	gotSERVFAIL bool
+	gotTimeout  bool
+	gotError    bool
 	hasRecords  bool
 }
 
@@ -499,6 +518,13 @@ func (r *Resolver) querySingleType(
 ) {
 	msg, err := r.queryDNS(ctx, nsIP, hostname, qtype)
 	if err != nil {
+		var netErr net.Error
+		if errors.As(err, &netErr) && netErr.Timeout() {
+			state.gotTimeout = true
+		} else {
+			state.gotError = true
+		}
+
 		return
 	}
 
@@ -540,13 +566,25 @@ func classifyResponse(resp *NameserverResponse, state queryState) {
 	switch {
 	case state.gotNXDomain && !state.hasRecords:
 		resp.Status = StatusNXDomain
-	case state.gotSERVFAIL && !state.hasRecords:
+	case state.gotTimeout && !state.hasRecords:
+		resp.Status = StatusTimeout
+		resp.Error = "all queries timed out"
+	case (state.gotError || state.gotSERVFAIL) && !state.hasRecords:
 		resp.Status = StatusError
+		resp.Error = errorMessageForState(state)
 	case !state.hasRecords && !state.gotNXDomain:
 		resp.Status = StatusNoData
 	}
 }
 
+func errorMessageForState(state queryState) string {
+	if state.gotSERVFAIL {
+		return "server returned SERVFAIL"
+	}
+
+	return "query failed due to non-timeout error"
+}
+
 // extractRecordValue formats a DNS RR value as a string.
 func extractRecordValue(rr dns.RR) string {
 	switch r := rr.(type) {

internal/resolver/resolver.go

@@ -17,6 +17,7 @@ const (
 	StatusError    = "error"
 	StatusNXDomain = "nxdomain"
 	StatusNoData   = "nodata"
+	StatusTimeout  = "timeout"
 )
 
 // MaxCNAMEDepth is the maximum CNAME chain depth to follow.

internal/resolver/resolver_test.go

@@ -10,6 +10,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/miekg/dns"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
@@ -622,6 +623,59 @@ func TestQueryAllNameservers_ContextCanceled(t *testing.T) {
 	assert.Error(t, err)
 }
 
+// ----------------------------------------------------------------
+// Timeout tests
+// ----------------------------------------------------------------
+
+func TestQueryNameserverIP_Timeout(t *testing.T) {
+	t.Parallel()
+
+	log := slog.New(slog.NewTextHandler(
+		os.Stderr,
+		&slog.HandlerOptions{Level: slog.LevelDebug},
+	))
+
+	r := resolver.NewFromLoggerWithClient(
+		log, &timeoutClient{},
+	)
+
+	ctx, cancel := context.WithTimeout(
+		context.Background(), 10*time.Second,
+	)
+	t.Cleanup(cancel)
+
+	// Query any IP — the client always returns a timeout error.
+	resp, err := r.QueryNameserverIP(
+		ctx, "unreachable.test.", "192.0.2.1",
+		"example.com",
+	)
+	require.NoError(t, err)
+
+	assert.Equal(t, resolver.StatusTimeout, resp.Status)
+	assert.NotEmpty(t, resp.Error)
+}
+
+// timeoutClient simulates DNS timeout errors for testing.
+type timeoutClient struct{}
+
+func (c *timeoutClient) ExchangeContext(
+	_ context.Context,
+	_ *dns.Msg,
+	_ string,
+) (*dns.Msg, time.Duration, error) {
+	return nil, 0, &net.OpError{
+		Op:  "read",
+		Net: "udp",
+		Err: &timeoutError{},
+	}
+}
+
+type timeoutError struct{}
+
+func (e *timeoutError) Error() string   { return "i/o timeout" }
+func (e *timeoutError) Timeout() bool   { return true }
+func (e *timeoutError) Temporary() bool { return true }
+
 func TestResolveIPAddresses_ContextCanceled(t *testing.T) {
 	t.Parallel()