tunnel: linkmtu, tunmtu as separate inputs

Author: ignoramous

intra/tun2socks.go

@@ -66,30 +66,34 @@ func init() {
 // Connect creates firestack-administered tunnel.
 // `fd` is the TUN device. The tunnel acquires an additional reference to it, which is
 // released by Disconnect(), so the caller must close `fd` and Disconnect() to close the TUN device.
-// `mtu` is the MTU of the TUN device.
+// `linkmtu` is the MTU of the underlying link (actual network). If <= 0, it is assumed to be same as `tunmtu`.
+// `tunmtu` is the MTU of the TUN device. This can be "faked", ie set to values larger than linkmtu. Typically, its value is same as `linkmtu`.
 // `ifaddrs` is a comma-separated list of interface addresses with prefix lengths, "ip/prefixlen".
 // `fakedns` is a comman-separated list of the nameservers that the system believes it is using, in "host:port" style.
 // `bdg` is a kotlin object that implements the Bridge interface.
 // `dtr` is the DefaultDNS (see: intra.NewDefaultDNS); can be nil. Changeable via intra.AddDefaultTransport.
 // Throws an exception if the TUN file descriptor cannot be opened, or if the tunnel fails to
 // connect.
-func Connect(fd, mtu int, ifaddrs, fakedns string, dtr DefaultDNS, bdg Bridge) (t Tunnel, err error) {
-	return NewTunnel(fd, mtu, ifaddrs, fakedns, dtr, bdg)
+func Connect(fd, linkmtu, tunmtu int, ifaddrs, fakedns string, dtr DefaultDNS, bdg Bridge) (t Tunnel, err error) {
+	if linkmtu <= 0 {
+		NewTunnel(fd, tunmtu, ifaddrs, fakedns, dtr, bdg)
+	}
+	return NewTunnel2(fd, linkmtu, tunmtu, ifaddrs, fakedns, dtr, bdg)
 }
 
-// Connect2 is like Connect, but assumes defaults for ifaddrs and fakedns
-// as ["10.111.222.1/24", "fd66:f83a:c650::0/120"] and ["10.111.222.3", "fd66:f83a:c650::3"]
+// Connect2 is like Connect, but assumes defaults for linkmtu, ifaddrs, and fakedns
+// as -1, ["10.111.222.1/24", "fd66:f83a:c650::0/120"], and ["10.111.222.3", "fd66:f83a:c650::3"]
 // respectively.
-func Connect2(fd, mtu int, dtr DefaultDNS, bdg Bridge) (t Tunnel, err error) {
+func Connect2(fd, tunmtu int, dtr DefaultDNS, bdg Bridge) (t Tunnel, err error) {
 	// usually, 10.111.222.0/24 / [fd66:f83a:c650::0]/120
 	// github.com/celzero/rethink-app/blob/59aa0daae/app/src/main/java/com/celzero/bravedns/service/BraveVPNService.kt#L2813
-	return NewTunnel(fd, mtu, "10.111.222.1/24,fd66:f83a:c650::0/120", "10.111.222.3,fd66:f83a:c650::3", nil, bdg)
+	return Connect(fd, -1, tunmtu, "10.111.222.1/24,fd66:f83a:c650::0/120", "10.111.222.3,fd66:f83a:c650::3", nil, bdg)
 }
 
 // Connect3 is like Connect2, but does not require passing a Default DNS resolver.
 // The tunnel will instead attempt to use the system DNS resolver (best effort).
-func Connect3(fd, mtu int, bdg Bridge) (t Tunnel, err error) {
-	return Connect2(fd, mtu, nil, bdg)
+func Connect3(fd, tunmtu int, bdg Bridge) (t Tunnel, err error) {
+	return Connect2(fd, tunmtu, nil, bdg)
 }
 
 // ControlledRouter creates a [backend.Router] over a [backend.Internet] proxy (like [backend.Exit]),