add config option for control URL

Closes #22

Co-authored-by: ChibangLW <ich@leonlenzen.de>
Signed-off-by: Will Norris <will@tailscale.com>

Author: willnorris

app.go

@@ -25,6 +25,9 @@ type TSApp struct {
 	// Ephemeral specifies whether Tailscale nodes should be registered as ephemeral.
 	Ephemeral bool `json:"ephemeral,omitempty" caddy:"namespace=tailscale.ephemeral"`
 
+	// ControlURL specifies the default control URL to use for nodes.
+	ControlURL string `json:"control_url,omitempty" caddy:"namespace=tailscale.control_url"`
+
 	// Nodes is a map of per-node configuration which overrides global options.
 	Nodes map[string]TSNode `json:"nodes,omitempty" caddy:"namespace=tailscale"`
 
@@ -41,6 +44,9 @@ type TSNode struct {
 	// Ephemeral specifies whether the node should be registered as ephemeral.
 	Ephemeral bool `json:"ephemeral,omitempty" caddy:"namespace=tailscale.ephemeral"`
 
+	// ControlURL specifies the control URL to use for the node.
+	ControlURL string `json:"control_url,omitempty" caddy:"namespace=tailscale.control_url"`
+
 	name string
 }
 
@@ -119,6 +125,11 @@ func parseTSNode(d *caddyfile.Dispenser) (TSNode, error) {
 				return node, segment.ArgErr()
 			}
 			node.AuthKey = segment.Val()
+		case "control_url":
+			if !segment.NextArg() {
+				return node, segment.ArgErr()
+			}
+			node.ControlURL = segment.Val()
 		case "ephemeral":
 			node.Ephemeral = true
 		default:

module.go

@@ -114,6 +114,9 @@ func getNode(ctx caddy.Context, name string) (*tailscaleNode, error) {
 		if s.AuthKey, err = getAuthKey(name, app); err != nil {
 			app.logger.Warn("error parsing auth key", zap.Error(err))
 		}
+		if s.ControlURL, err = getControlURL(name, app); err != nil {
+			app.logger.Warn("error parsing control URL", zap.Error(err))
+		}
 
 		if name != "" {
 			// Set config directory for tsnet.  By default, tsnet will use the name of the
@@ -179,6 +182,19 @@ func getEphemeral(name string, app *TSApp) bool {
 	return app.Ephemeral
 }
 
+func getControlURL(name string, app *TSApp) (string, error) {
+	if app == nil {
+		return "", nil
+	}
+	if node, ok := app.Nodes[name]; ok {
+		if node.ControlURL != "" {
+			return repl.ReplaceOrErr(node.ControlURL, true, true)
+		}
+	}
+
+	return repl.ReplaceOrErr(app.ControlURL, true, true)
+}
+
 // tailscaleNode is a wrapper around a tsnet.Server that provides a fully self-contained Tailscale node.
 // This node can listen on the tailscale network interface, or be used to connect to other nodes in the tailnet.
 type tailscaleNode struct {