tailcfg: bump, document MapRequest.Version value

Fixes tailscale/corp#634

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

control/controlclient/direct.go

@@ -530,16 +530,14 @@ func (c *Direct) PollNetMap(ctx context.Context, maxPolls int, cb func(*NetworkM
 	}
 
 	request := tailcfg.MapRequest{
-		Version:     4,
-		IncludeIPv6: true,
-		DeltaPeers:  true,
-		KeepAlive:   c.keepAlive,
-		NodeKey:     tailcfg.NodeKey(persist.PrivateNodeKey.Public()),
-		DiscoKey:    c.discoPubKey,
-		Endpoints:   ep,
-		Stream:      allowStream,
-		Hostinfo:    hostinfo,
-		DebugFlags:  c.debugFlags,
+		Version:    5,
+		KeepAlive:  c.keepAlive,
+		NodeKey:    tailcfg.NodeKey(persist.PrivateNodeKey.Public()),
+		DiscoKey:   c.discoPubKey,
+		Endpoints:  ep,
+		Stream:     allowStream,
+		Hostinfo:   hostinfo,
+		DebugFlags: c.debugFlags,
 	}
 	if c.newDecompressor != nil {
 		request.Compress = "zstd"

tailcfg/tailcfg.go

@@ -461,17 +461,23 @@ type RegisterResponse struct {
 // using the local machine key, and sent to:
 //	https://login.tailscale.com/machine/<mkey hex>/map
 type MapRequest struct {
-	Version            int    // current version is 4
-	Compress           string // "zstd" or "" (no compression)
-	KeepAlive          bool   // whether server should send keep-alives back to us
-	NodeKey            NodeKey
-	DiscoKey           DiscoKey
-	Endpoints          []string // caller's endpoints (IPv4 or IPv6)
-	IncludeIPv6        bool     // include IPv6 endpoints in returned Node Endpoints
-	IncludeIPv6Overlay bool     // include IPv6 Addresses and AllowedIPs in returned Nodes.
-	DeltaPeers         bool     // whether the 2nd+ network map in response should be deltas, using PeersChanged, PeersRemoved
-	Stream             bool     // if true, multiple MapResponse objects are returned
-	Hostinfo           *Hostinfo
+	// Version is incremented whenever the client code changes enough that
+	// we want to signal to the control server that we're capable of something
+	// different.
+	//
+	// History of versions:
+	//     3: implicit compression, keep-alives
+	//     4: opt-in keep-alives via KeepAlive field, opt-in compression via Compress
+	//     5: 2020-10-19, implies IncludeIPv6, DeltaPeers/DeltaUserProfiles, supports MagicDNS
+	Version     int
+	Compress    string // "zstd" or "" (no compression)
+	KeepAlive   bool   // whether server should send keep-alives back to us
+	NodeKey     NodeKey
+	DiscoKey    DiscoKey
+	Endpoints   []string // caller's endpoints (IPv4 or IPv6)
+	IncludeIPv6 bool     `json:",omitempty"` // include IPv6 endpoints in returned Node Endpoints (for Version 4 clients)
+	Stream      bool     // if true, multiple MapResponse objects are returned
+	Hostinfo    *Hostinfo
 
 	// ReadOnly is whether the client just wants to fetch the
 	// MapResponse, without updating their Endpoints. The