cmd/vnet: add --blend and --pcap flags

Updates #13038

Change-Id: Id16ea9eb94447a3d9651215f04b2525daf10b3eb
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/vnet/vnet-main.go

@@ -27,6 +27,8 @@ var (
 	nat2     = flag.String("nat2", "hard", "type of NAT to use for second network")
 	portmap  = flag.Bool("portmap", false, "enable portmapping")
 	dgram    = flag.Bool("dgram", false, "enable datagram mode; for use with macOS Hypervisor.Framework and VZFileHandleNetworkDeviceAttachment")
+	blend    = flag.Bool("blend", true, "blend reality (controlplane.tailscale.com and DERPs) into the virtual network")
+	pcapFile = flag.String("pcap", "", "if non-empty, filename to write pcap")
 )
 
 func main() {
@@ -57,6 +59,8 @@ func main() {
 	}
 
 	var c vnet.Config
+	c.SetPCAPFile(*pcapFile)
+	c.SetBlendReality(*blend)
 	node1 := c.AddNode(c.AddNetwork("2.1.1.1", "192.168.1.1/24", vnet.NAT(*nat)))
 	c.AddNode(c.AddNetwork("2.2.2.2", "10.2.0.1/16", vnet.NAT(*nat2)))
 	if *portmap {

tstest/natlab/vnet/conf.go

@@ -32,16 +32,28 @@ type Config struct {
 	nodes        []*Node
 	networks     []*Network
 	pcapFile     string
+	blendReality bool
 }
 
+// SetPCAPFile sets the filename to write a pcap file to,
+// or empty to disable pcap file writing.
 func (c *Config) SetPCAPFile(file string) {
 	c.pcapFile = file
 }
 
+// NumNodes returns the number of nodes in the configuration.
 func (c *Config) NumNodes() int {
 	return len(c.nodes)
 }
 
+// SetBlendReality sets whether to blend the real controlplane.tailscale.com and
+// DERP servers into the virtual network. This is mostly useful for interactive
+// testing when working on natlab.
+func (c *Config) SetBlendReality(v bool) {
+	c.blendReality = v
+}
+
+// FirstNetwork returns the first network in the config, or nil if none.
 func (c *Config) FirstNetwork() *Network {
 	if len(c.networks) == 0 {
 		return nil