control/controlclient: let clients opt in to Sharer-vs-User split model

Updates tailscale/corp#1183

control/controlclient/direct.go

@@ -117,6 +117,7 @@ type Direct struct {
 	discoPubKey            tailcfg.DiscoKey
 	machinePrivKey         wgkey.Private
 	debugFlags             []string
+	keepSharerAndUserSplit bool
 
 	mu           sync.Mutex // mutex guards the following fields
 	serverKey    wgkey.Key
@@ -144,6 +145,10 @@ type Options struct {
 	Logf              logger.Logf
 	HTTPTestClient    *http.Client // optional HTTP client to use (for tests only)
 	DebugFlags        []string     // debug settings to send to control
+
+	// KeepSharerAndUserSplit controls whether the client
+	// understands Node.Sharer. If false, the Sharer is mapped to the User.
+	KeepSharerAndUserSplit bool
 }
 
 type Decompressor interface {
@@ -201,6 +206,7 @@ func NewDirect(opts Options) (*Direct, error) {
 		authKey:                opts.AuthKey,
 		discoPubKey:            opts.DiscoPublicKey,
 		debugFlags:             opts.DebugFlags,
+		keepSharerAndUserSplit: opts.KeepSharerAndUserSplit,
 	}
 	if opts.Hostinfo == nil {
 		c.SetHostinfo(NewHostinfo())
@@ -785,20 +791,13 @@ func (c *Direct) sendMapRequest(ctx context.Context, maxPolls int, cb func(*Netw
 		}
 		addUserProfile(nm.User)
 		for _, peer := range resp.Peers {
-			// TODO(bradfitz): ideally we'd push down the semantically correct
-			// Nodes with differing User vs Sharer fields, but that means
-			// updating Windows, macOS, and tailscale status to respect all
-			// those fields, but until we have a plan for what the UI should
-			// be later when we treat them differently, it's easier to just
-			// merge it together here. The server will anonymize UserProfile
-			// records of those not in your network and not a sharer, which
-			// will be most of the peer.Users so it'll be rare when a node's
-			// owner-who's-different-from-sharer will have a non-scrubbed
-			// UserProfile: they would've also needed to share a node
-			// themselves.  Until we care, merge the data here.
 			if !peer.Sharer.IsZero() {
+				if c.keepSharerAndUserSplit {
+					addUserProfile(peer.Sharer)
+				} else {
 					peer.User = peer.Sharer
 				}
+			}
 			addUserProfile(peer.User)
 		}
 		if resp.Node.MachineAuthorized {