tailcfg, control/controlclient: make nil PacketFilter mean unchanged (mapver 6)

After mapver 5's incremental netmap updates & user profiles, much of
the remaining bandwidth for streamed MapResponses were redundant,
unchanged PacketFilters. So make MapRequest.Version 6 mean that nil
means unchanged from the previous value.

control/controlclient/direct.go

@@ -45,6 +45,7 @@ import (
 	"tailscale.com/types/opt"
 	"tailscale.com/types/structs"
 	"tailscale.com/version"
+	"tailscale.com/wgengine/filter"
 )
 
 type Persist struct {
@@ -541,7 +542,7 @@ func (c *Direct) PollNetMap(ctx context.Context, maxPolls int, cb func(*NetworkM
 	}
 
 	request := tailcfg.MapRequest{
-		Version:    5,
+		Version:    6,
 		KeepAlive:  c.keepAlive,
 		NodeKey:    tailcfg.NodeKey(persist.PrivateNodeKey.Public()),
 		DiscoKey:   c.discoPubKey,
@@ -636,6 +637,7 @@ func (c *Direct) PollNetMap(ctx context.Context, maxPolls int, cb func(*NetworkM
 
 	var lastDERPMap *tailcfg.DERPMap
 	var lastUserProfile = map[tailcfg.UserID]tailcfg.UserProfile{}
+	var lastParsedPacketFilter []filter.Match
 
 	// If allowStream, then the server will use an HTTP long poll to
 	// return incremental results. There is always one response right
@@ -713,6 +715,10 @@ func (c *Direct) PollNetMap(ctx context.Context, maxPolls int, cb func(*NetworkM
 			resp.Peers = filtered
 		}
 
+		if pf := resp.PacketFilter; pf != nil {
+			lastParsedPacketFilter = c.parsePacketFilter(pf)
+		}
+
 		nm := &NetworkMap{
 			NodeKey:      tailcfg.NodeKey(persist.PrivateNodeKey.Public()),
 			PrivateKey:   persist.PrivateNodeKey,
@@ -727,7 +733,7 @@ func (c *Direct) PollNetMap(ctx context.Context, maxPolls int, cb func(*NetworkM
 			Domain:       resp.Domain,
 			DNS:          resp.DNSConfig,
 			Hostinfo:     resp.Node.Hostinfo,
-			PacketFilter: c.parsePacketFilter(resp.PacketFilter),
+			PacketFilter: lastParsedPacketFilter,
 			DERPMap:      lastDERPMap,
 			Debug:        resp.Debug,
 		}

tailcfg/tailcfg.go

@@ -476,6 +476,7 @@ type MapRequest struct {
 	//     3: implicit compression, keep-alives
 	//     4: opt-in keep-alives via KeepAlive field, opt-in compression via Compress
 	//     5: 2020-10-19, implies IncludeIPv6, delta Peers/UserProfiles, supports MagicDNS
+	//     6: 2020-12-07: means MapResponse.PacketFilter nil means unchanged
 	Version     int
 	Compress    string // "zstd" or "" (no compression)
 	KeepAlive   bool   // whether server should send keep-alives back to us
@@ -620,11 +621,25 @@ type MapResponse struct {
 	SearchPaths []string  `json:",omitempty"`
 	DNSConfig   DNSConfig `json:",omitempty"`
 
-	// ACLs
+	// Domain is the name of the network that this node is
+	// in. It's either of the form "example.com" (for user
+	// foo@example.com, for multi-user networks) or
+	// "foo@gmail.com" (for siloed users on shared email
+	// providers). Its exact form should not be depended on; new
+	// forms are coming later.
 	Domain string
+
+	// PacketFilter are the firewall rules.
+	//
+	// For MapRequest.Version >= 6, a nil value means the most
+	// previously streamed non-nil MapResponse.PacketFilter within
+	// the same HTTP response. A non-nil but empty list always means
+	// no PacketFilter (that is, to block everything).
 	PacketFilter []FilterRule
-	UserProfiles []UserProfile // as of 1.1.541: may be new or updated user profiles only
+
+	UserProfiles []UserProfile // as of 1.1.541 (mapver 5): may be new or updated user profiles only
 	Roles        []Role        // deprecated; clients should not rely on Roles
+
 	// TODO: Groups       []Group
 	// TODO: Capabilities []Capability
 

version/version.go

@@ -10,7 +10,7 @@ package version
 // Long is a full version number for this build, of the form
 // "x.y.z-commithash", or "date.yyyymmdd" if no actual version was
 // provided.
-const Long = "date.20201203"
+const Long = "date.20201207"
 
 // Short is a short version number for this build, of the form
 // "x.y.z", or "date.yyyymmdd" if no actual version was provided.