Add session context outbounds as slice (#3356)

* Add session context outbounds as slice

slice is needed for dialer proxy where two outbounds work on top of each other
There are two sets of target addr for example
It also enable Xtls to correctly do splice copy by checking both outbounds are ready to do direct copy

* Fill outbound tag info

* Splice now checks capalibility from all outbounds

* Fix unit tests

proxy/shadowsocks_2022/inbound.go

@@ -66,7 +66,7 @@ func (i *Inbound) Network() []net.Network {
 func (i *Inbound) Process(ctx context.Context, network net.Network, connection stat.Connection, dispatcher routing.Dispatcher) error {
 	inbound := session.InboundFromContext(ctx)
 	inbound.Name = "shadowsocks-2022"
-	inbound.SetCanSpliceCopy(3)
+	inbound.CanSpliceCopy = 3
 
 	var metadata M.Metadata
 	if inbound.Source.IsValid() {

proxy/shadowsocks_2022/inbound_multi.go

@@ -155,7 +155,7 @@ func (i *MultiUserInbound) Network() []net.Network {
 func (i *MultiUserInbound) Process(ctx context.Context, network net.Network, connection stat.Connection, dispatcher routing.Dispatcher) error {
 	inbound := session.InboundFromContext(ctx)
 	inbound.Name = "shadowsocks-2022-multi"
-	inbound.SetCanSpliceCopy(3)
+	inbound.CanSpliceCopy = 3
 
 	var metadata M.Metadata
 	if inbound.Source.IsValid() {

proxy/shadowsocks_2022/inbound_relay.go

@@ -87,7 +87,7 @@ func (i *RelayInbound) Network() []net.Network {
 func (i *RelayInbound) Process(ctx context.Context, network net.Network, connection stat.Connection, dispatcher routing.Dispatcher) error {
 	inbound := session.InboundFromContext(ctx)
 	inbound.Name = "shadowsocks-2022-relay"
-	inbound.SetCanSpliceCopy(3)
+	inbound.CanSpliceCopy = 3
 
 	var metadata M.Metadata
 	if inbound.Source.IsValid() {

proxy/shadowsocks_2022/outbound.go

@@ -65,15 +65,16 @@ func (o *Outbound) Process(ctx context.Context, link *transport.Link, dialer int
 	inbound := session.InboundFromContext(ctx)
 	if inbound != nil {
 		inboundConn = inbound.Conn
-		inbound.SetCanSpliceCopy(3)
 	}
 
-	outbound := session.OutboundFromContext(ctx)
-	if outbound == nil || !outbound.Target.IsValid() {
+	outbounds := session.OutboundsFromContext(ctx)
+	ob := outbounds[len(outbounds) - 1]
+	if !ob.Target.IsValid() {
 		return newError("target not specified")
 	}
-	outbound.Name = "shadowsocks-2022"
-	destination := outbound.Target
+	ob.Name = "shadowsocks-2022"
+	ob.CanSpliceCopy = 3
+	destination := ob.Target
 	network := destination.Network
 
 	newError("tunneling request to ", destination, " via ", o.server.NetAddr()).WriteToLog(session.ExportIDToError(ctx))