dnsx/cacher: barriered ans as cached ans (mk 2)

intra/core/barrier.go

@@ -19,6 +19,11 @@ import (
 	"time"
 )
 
+const (
+	Anew = iota
+	Shared
+)
+
 // V is an in-flight or completed Barrier.Do V
 type V struct {
 	wg  sync.WaitGroup
@@ -66,21 +71,21 @@ func (ba *Barrier) addLocked(k string) *V {
 // sure that only one execution is in-flight for a given key at a
 // time. If a duplicate comes in, the duplicate caller waits for the
 // original to complete and receives the same results.
-func (ba *Barrier) Do(k string, me func() (any, error)) *V {
+func (ba *Barrier) Do(k string, me func() (any, error)) (*V, int) {
 	ba.mu.Lock()
 	c, ok := ba.getLocked(k)
 	if ok {
 		ba.mu.Unlock()
 
 		c.N.Add(1)
 		c.wg.Wait() // wait for the in-flight req to complete
-		return c
+		return c, Shared
 	}
 	c = ba.addLocked(k)
 	ba.mu.Unlock()
 
 	c.Val, c.Err = me()
 
 	c.wg.Done() // unblock all waiters
-	return c
+	return c, Anew
 }

intra/dnsx/cacher.go

@@ -300,18 +300,11 @@ func (t *ctransport) Type() string {
 }
 
 func (t *ctransport) fetch(network string, q []byte, msg *dns.Msg, summary *Summary, cb *cache, key string) (r []byte, err error) {
-	sendRequest := func(async bool) ([]byte, error) {
-		var finalsumm *Summary
-		if async {
-			finalsumm = new(Summary)
-		} else {
-			finalsumm = summary
-		}
-
+	sendRequest := func(finalsumm *Summary) ([]byte, error) {
 		finalsumm.ID = t.Transport.ID()
 		finalsumm.Type = t.Transport.Type()
 
-		rv := t.reqbarrier.Do(key, func() (any, error) {
+		rv, st := t.reqbarrier.Do(key, func() (any, error) {
 			ans, err := t.Transport.Query(network, q, finalsumm)
 			cb.put(ans, finalsumm)
 			return &cres{ans: xdns.AsMsg(ans), s: finalsumm}, err
@@ -322,9 +315,14 @@ func (t *ctransport) fetch(network string, q []byte, msg *dns.Msg, summary *Summ
 			return nil, errCacheResponseMismatch
 		}
 
+		// if rv is "shared", then use this req's summary over the "shared" one
+		if st == core.Shared {
+			cachedres.s = finalsumm
+		}
+
 		finalres, origsumm, finalerr := asResponse(msg, cachedres, true)
 		// fill summary regardless of errors
-		origsumm.FillInto(finalsumm) // origsumm may be equal to s
+		origsumm.FillInto(finalsumm) // origsumm may be equal to finalsumm
 
 		return finalres, errors.Join(rv.Err, finalerr)
 	}
@@ -353,7 +351,7 @@ func (t *ctransport) fetch(network string, q []byte, msg *dns.Msg, summary *Summ
 			// fallthrough to sendRequest
 		} else if cachedsummary != nil {
 			if !isfresh { // not fresh, fetch in the background
-				go sendRequest(true)
+				go sendRequest(new(Summary))
 			}
 			// change summary fields to reflect cached response, except for latency
 			cachedsummary.FillInto(summary)
@@ -362,7 +360,8 @@ func (t *ctransport) fetch(network string, q []byte, msg *dns.Msg, summary *Summ
 			return
 		} // else: fallthrough to sendRequest
 	}
-	return sendRequest(false) // summary is filled by underlying transport
+
+	return sendRequest(summary) // summary is filled by underlying transport
 }
 
 func (t *ctransport) Query(network string, q []byte, summary *Summary) ([]byte, error) {

intra/ipn/wgnet.go

@@ -573,7 +573,7 @@ func (tnet *wgtun) DialContext(ctx context.Context, network, address string) (ne
 		}
 	}
 
-	rv := tnet.reqbarrier.Do(host, func() (any, error) {
+	rv, _ := tnet.reqbarrier.Do(host, func() (any, error) {
 		return tnet.LookupContextHost(ctx, host)
 	})
 	if rv.Err != nil {