Add API functions for manipulating maximum session MTU, fix TUN/TAP to use that

src/tuntap/tun.go

@@ -35,6 +35,7 @@ const tun_ETHER_HEADER_LENGTH = 14
 // you should pass this object to the yggdrasil.SetRouterAdapter() function
 // before calling yggdrasil.Start().
 type TunAdapter struct {
+	core        *yggdrasil.Core
 	writer      tunWriter
 	reader      tunReader
 	config      *config.NodeState
@@ -131,6 +132,7 @@ func (tun *TunAdapter) Init(core *yggdrasil.Core, config *config.NodeState, log
 	if !ok {
 		return fmt.Errorf("invalid options supplied to TunAdapter module")
 	}
+	tun.core = core
 	tun.config = config
 	tun.log = log
 	tun.listener = tunoptions.Listener
@@ -181,6 +183,7 @@ func (tun *TunAdapter) _start() error {
 	if tun.MTU() != current.IfMTU {
 		tun.log.Warnf("Warning: Interface MTU %d automatically adjusted to %d (supported range is 1280-%d)", current.IfMTU, tun.MTU(), MaximumMTU(tun.IsTAP()))
 	}
+	tun.core.SetMaximumSessionMTU(uint16(tun.MTU()))
 	tun.isOpen = true
 	go tun.handler()
 	tun.reader.Act(nil, tun.reader._read) // Start the reader

src/yggdrasil/api.go

@@ -363,6 +363,22 @@ func (c *Core) SetNodeInfo(nodeinfo interface{}, nodeinfoprivacy bool) {
 	c.router.nodeinfo.setNodeInfo(nodeinfo, nodeinfoprivacy)
 }
 
+// GetMaximumSessionMTU returns the maximum allowed session MTU size.
+func (c *Core) GetMaximumSessionMTU(mtu uint16) uint16 {
+	return c.router.sessions.myMaximumMTU
+}
+
+// SetMaximumSessionMTU sets the maximum allowed session MTU size. The return
+// value contains the actual set value, since Yggdrasil will not accept MTUs
+// below 1280 bytes. The default value is 65535 bytes.
+func (c *Core) SetMaximumSessionMTU(mtu uint16) uint16 {
+	if mtu < 1280 {
+		mtu = 1280
+	}
+	c.router.sessions.myMaximumMTU = mtu
+	return mtu
+}
+
 // GetNodeInfo requests nodeinfo from a remote node, as specified by the public
 // key and coordinates specified. The third parameter specifies whether a cached
 // result is acceptable - this results in less traffic being generated than is

src/yggdrasil/session.go

@@ -121,6 +121,7 @@ type sessions struct {
 	lastCleanup      time.Time
 	isAllowedHandler func(pubkey *crypto.BoxPubKey, initiator bool) bool // Returns true or false if session setup is allowed
 	isAllowedMutex   sync.RWMutex                                        // Protects the above
+	myMaximumMTU     uint16                                              // Maximum allowed session MTU
 	permShared       map[crypto.BoxPubKey]*crypto.BoxSharedKey           // Maps known permanent keys to their shared key, used by DHT a lot
 	sinfos           map[crypto.Handle]*sessionInfo                      // Maps handle onto session info
 	byTheirPerm      map[crypto.BoxPubKey]*crypto.Handle                 // Maps theirPermPub onto handle
@@ -133,6 +134,7 @@ func (ss *sessions) init(r *router) {
 	ss.sinfos = make(map[crypto.Handle]*sessionInfo)
 	ss.byTheirPerm = make(map[crypto.BoxPubKey]*crypto.Handle)
 	ss.lastCleanup = time.Now()
+	ss.myMaximumMTU = 65535
 }
 
 func (ss *sessions) reconfigure() {
@@ -187,9 +189,9 @@ func (ss *sessions) createSession(theirPermKey *crypto.BoxPubKey) *sessionInfo {
 	sinfo.mySesPriv = *priv
 	sinfo.myNonce = *crypto.NewBoxNonce()
 	sinfo.theirMTU = 1280
-	ss.router.core.config.Mutex.RLock()
-	sinfo.myMTU = uint16(ss.router.core.config.Current.IfMTU)
-	ss.router.core.config.Mutex.RUnlock()
+	// TODO: sinfo.myMTU becomes unnecessary if we always have a reference to the
+	// sessions struct so let's check if that is the case
+	sinfo.myMTU = ss.myMaximumMTU
 	now := time.Now()
 	sinfo.timeOpened = now
 	sinfo.time = now