Revert "[client] Add TTL-based refresh to mgmt DNS cache via handler chain (#5945)"

This reverts commit 801de8c68d.

client/internal/dns/handler_chain.go

@@ -1,10 +1,7 @@
 package dns
 
 import (
-	"context"
 	"fmt"
-	"math"
-	"net"
 	"slices"
 	"strconv"
 	"strings"
@@ -195,12 +192,6 @@ func (c *HandlerChain) logHandlers() {
 }
 
 func (c *HandlerChain) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
-	c.dispatch(w, r, math.MaxInt)
-}
-
-// dispatch routes a DNS request through the chain, skipping handlers with
-// priority > maxPriority. Shared by ServeDNS and ResolveInternal.
-func (c *HandlerChain) dispatch(w dns.ResponseWriter, r *dns.Msg, maxPriority int) {
 	if len(r.Question) == 0 {
 		return
 	}
@@ -225,9 +216,6 @@ func (c *HandlerChain) dispatch(w dns.ResponseWriter, r *dns.Msg, maxPriority in
 
 	// Try handlers in priority order
 	for _, entry := range handlers {
-		if entry.Priority > maxPriority {
-			continue
-		}
 		if !c.isHandlerMatch(qname, entry) {
 			continue
 		}
@@ -285,55 +273,6 @@ func (c *HandlerChain) logResponse(logger *log.Entry, cw *ResponseWriterChain, q
 		cw.response.Len(), meta, time.Since(startTime))
 }
 
-// ResolveInternal runs an in-process DNS query against the chain, skipping any
-// handler with priority > maxPriority. Used by internal callers (e.g. the mgmt
-// cache refresher) that must bypass themselves to avoid loops. Honors ctx
-// cancellation; on ctx.Done the dispatch goroutine is left to drain on its own
-// (bounded by the invoked handler's internal timeout).
-func (c *HandlerChain) ResolveInternal(ctx context.Context, r *dns.Msg, maxPriority int) (*dns.Msg, error) {
-	if len(r.Question) == 0 {
-		return nil, fmt.Errorf("empty question")
-	}
-
-	base := &internalResponseWriter{}
-	done := make(chan struct{})
-	go func() {
-		c.dispatch(base, r, maxPriority)
-		close(done)
-	}()
-
-	select {
-	case <-done:
-	case <-ctx.Done():
-		// Prefer a completed response if dispatch finished concurrently with cancellation.
-		select {
-		case <-done:
-		default:
-			return nil, fmt.Errorf("resolve %s: %w", strings.ToLower(r.Question[0].Name), ctx.Err())
-		}
-	}
-
-	if base.response == nil || base.response.Rcode == dns.RcodeRefused {
-		return nil, fmt.Errorf("no handler resolved %s at priority ≤ %d",
-			strings.ToLower(r.Question[0].Name), maxPriority)
-	}
-	return base.response, nil
-}
-
-// HasRootHandlerAtOrBelow reports whether any "." handler is registered at
-// priority ≤ maxPriority.
-func (c *HandlerChain) HasRootHandlerAtOrBelow(maxPriority int) bool {
-	c.mu.RLock()
-	defer c.mu.RUnlock()
-
-	for _, h := range c.handlers {
-		if h.Pattern == "." && h.Priority <= maxPriority {
-			return true
-		}
-	}
-	return false
-}
-
 func (c *HandlerChain) isHandlerMatch(qname string, entry HandlerEntry) bool {
 	switch {
 	case entry.Pattern == ".":
@@ -352,36 +291,3 @@ func (c *HandlerChain) isHandlerMatch(qname string, entry HandlerEntry) bool {
 		}
 	}
 }
-
-// internalResponseWriter captures a dns.Msg for in-process chain queries.
-type internalResponseWriter struct {
-	response *dns.Msg
-}
-
-func (w *internalResponseWriter) WriteMsg(m *dns.Msg) error { w.response = m; return nil }
-func (w *internalResponseWriter) LocalAddr() net.Addr       { return nil }
-func (w *internalResponseWriter) RemoteAddr() net.Addr      { return nil }
-
-// Write unpacks raw DNS bytes so handlers that call Write instead of WriteMsg
-// still surface their answer to ResolveInternal.
-func (w *internalResponseWriter) Write(p []byte) (int, error) {
-	msg := new(dns.Msg)
-	if err := msg.Unpack(p); err != nil {
-		return 0, err
-	}
-	w.response = msg
-	return len(p), nil
-}
-
-func (w *internalResponseWriter) Close() error      { return nil }
-func (w *internalResponseWriter) TsigStatus() error { return nil }
-
-// TsigTimersOnly is part of dns.ResponseWriter.
-func (w *internalResponseWriter) TsigTimersOnly(bool) {
-	// no-op: in-process queries carry no TSIG state.
-}
-
-// Hijack is part of dns.ResponseWriter.
-func (w *internalResponseWriter) Hijack() {
-	// no-op: in-process queries have no underlying connection to hand off.
-}