types/views: add Slice.All iterator

And convert a few callers as an example, but nowhere near all.

Updates #12912

Change-Id: I5eaa12a29a6cd03b58d6f1072bd27bc0467852f2
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/local.go

@@ -2095,9 +2095,7 @@ func (b *LocalBackend) updateFilterLocked(netMap *netmap.NetworkMap, prefs ipn.P
 		}
 	}
 	if prefs.Valid() {
-		ar := prefs.AdvertiseRoutes()
-		for i := range ar.Len() {
-			r := ar.At(i)
+		for _, r := range prefs.AdvertiseRoutes().All() {
 			if r.Bits() == 0 {
 				// When offering a default route to the world, we
 				// filter out locally reachable LANs, so that the
@@ -2312,8 +2310,8 @@ func packetFilterPermitsUnlockedNodes(peers map[tailcfg.NodeID]tailcfg.NodeView,
 			continue
 		}
 		numUnlocked++
-		for i := range p.AllowedIPs().Len() { // not only addresses!
-			b.AddPrefix(p.AllowedIPs().At(i))
+		for _, pfx := range p.AllowedIPs().All() { // not only addresses!
+			b.AddPrefix(pfx)
 		}
 	}
 	if numUnlocked == 0 {
@@ -4105,15 +4103,14 @@ func dnsConfigForNetmap(nm *netmap.NetworkMap, peers map[tailcfg.NodeID]tailcfg.
 			return // TODO: propagate error?
 		}
 		var have4 bool
-		for i := range addrs.Len() {
-			if addrs.At(i).Addr().Is4() {
+		for _, addr := range addrs.All() {
+			if addr.Addr().Is4() {
 				have4 = true
 				break
 			}
 		}
 		var ips []netip.Addr
-		for i := range addrs.Len() {
-			addr := addrs.At(i)
+		for _, addr := range addrs.All() {
 			if selfV6Only {
 				if addr.Addr().Is6() {
 					ips = append(ips, addr.Addr())
@@ -4401,8 +4398,7 @@ func (b *LocalBackend) initPeerAPIListener() {
 	b.peerAPIServer = ps
 
 	isNetstack := b.sys.IsNetstack()
-	for i := range addrs.Len() {
-		a := addrs.At(i)
+	for i, a := range addrs.All() {
 		var ln net.Listener
 		var err error
 		skipListen := i > 0 && isNetstack
@@ -5263,8 +5259,8 @@ func (b *LocalBackend) setNetMapLocked(nm *netmap.NetworkMap) {
 		b.nodeByAddr[k] = 0
 	}
 	addNode := func(n tailcfg.NodeView) {
-		for i := range n.Addresses().Len() {
-			if ipp := n.Addresses().At(i); ipp.IsSingleIP() {
+		for _, ipp := range n.Addresses().All() {
+			if ipp.IsSingleIP() {
 				b.nodeByAddr[ipp.Addr()] = n.ID()
 			}
 		}

types/views/views.go

@@ -10,6 +10,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"iter"
 	"maps"
 	"reflect"
 	"slices"
@@ -208,6 +209,17 @@ type Slice[T any] struct {
 	ж []T
 }
 
+// All returns an iterator over v.
+func (v Slice[T]) All() iter.Seq2[int, T] {
+	return func(yield func(int, T) bool) {
+		for i, v := range v.ж {
+			if !yield(i, v) {
+				return
+			}
+		}
+	}
+}
+
 // MapKey returns a unique key for a slice, based on its address and length.
 func (v Slice[T]) MapKey() SliceMapKey[T] { return mapKey(v.ж) }
 

types/views/views_test.go

@@ -6,8 +6,10 @@ package views
 import (
 	"bytes"
 	"encoding/json"
+	"fmt"
 	"net/netip"
 	"reflect"
+	"slices"
 	"strings"
 	"testing"
 	"unsafe"
@@ -412,3 +414,15 @@ func TestContainsPointers(t *testing.T) {
 		})
 	}
 }
+
+func TestSliceRange(t *testing.T) {
+	sv := SliceOf([]string{"foo", "bar"})
+	var got []string
+	for i, v := range sv.All() {
+		got = append(got, fmt.Sprintf("%d-%s", i, v))
+	}
+	want := []string{"0-foo", "1-bar"}
+	if !slices.Equal(got, want) {
+		t.Errorf("got %q; want %q", got, want)
+	}
+}