cmd/tailscale, ipn/ipnlocal: add suggest exit node CLI option (#11407)

Updates tailscale/corp#17516

Signed-off-by: Claire Wang <claire@tailscale.com>

client/tailscale/apitype/apitype.go

@@ -49,3 +49,11 @@ type ReloadConfigResponse struct {
 	Reloaded bool   // whether the config was reloaded
 	Err      string // any error message
 }
+
+// ExitNodeSuggestionResponse is the response to a LocalAPI suggest-exit-node GET request.
+// It returns the StableNodeID, name, and location of a suggested exit node for the client making the request.
+type ExitNodeSuggestionResponse struct {
+	ID       tailcfg.StableNodeID
+	Name     string
+	Location tailcfg.LocationView `json:",omitempty"`
+}

client/tailscale/localclient.go

@@ -1514,3 +1514,12 @@ func (w *IPNBusWatcher) Next() (ipn.Notify, error) {
 	}
 	return n, nil
 }
+
+// SuggestExitNode requests an exit node suggestion and returns the exit node's details.
+func (lc *LocalClient) SuggestExitNode(ctx context.Context) (apitype.ExitNodeSuggestionResponse, error) {
+	body, err := lc.get200(ctx, "/localapi/v0/suggest-exit-node")
+	if err != nil {
+		return apitype.ExitNodeSuggestionResponse{}, err
+	}
+	return decodeJSON[apitype.ExitNodeSuggestionResponse](body)
+}