XTLS Vision: Refactor code to use DispatchLink() in VLESS inbound (#5076)

* Xtls: code refactor

- Move more logic to VisionReader/Writer
- Remove XtlsWrite()
- XtlsRead now only handle splice at the outbound
- This helps VLESS inbound to have simple buf.copy() so that we can remove pipe next

* Add bufferFlushNext; Use DispatchLink() in VLESS inbound

* Use TimeoutWrapperReader; clean up timer/buffer

proxy/vless/encoding/encoding.go

@@ -1,7 +1,6 @@
 package encoding
 
 import (
-	"bytes"
 	"context"
 	"io"
 
@@ -11,7 +10,6 @@ import (
 	"github.com/xtls/xray-core/common/protocol"
 	"github.com/xtls/xray-core/common/session"
 	"github.com/xtls/xray-core/common/signal"
-	"github.com/xtls/xray-core/features/stats"
 	"github.com/xtls/xray-core/proxy"
 	"github.com/xtls/xray-core/proxy/vless"
 )
@@ -171,8 +169,8 @@ func DecodeResponseHeader(reader io.Reader, request *protocol.RequestHeader) (*A
 	return responseAddons, nil
 }
 
-// XtlsRead filter and read xtls protocol
-func XtlsRead(reader buf.Reader, writer buf.Writer, timer *signal.ActivityTimer, conn net.Conn, input *bytes.Reader, rawInput *bytes.Buffer, trafficState *proxy.TrafficState, ob *session.Outbound, isUplink bool, ctx context.Context) error {
+// XtlsRead can switch to splice copy
+func XtlsRead(reader buf.Reader, writer buf.Writer, timer *signal.ActivityTimer, conn net.Conn, trafficState *proxy.TrafficState, isUplink bool, ctx context.Context) error {
 	err := func() error {
 		for {
 			if isUplink && trafficState.Inbound.UplinkReaderDirectCopy || !isUplink && trafficState.Outbound.DownlinkReaderDirectCopy {
@@ -181,74 +179,11 @@ func XtlsRead(reader buf.Reader, writer buf.Writer, timer *signal.ActivityTimer,
 				if inbound := session.InboundFromContext(ctx); inbound != nil && inbound.Conn != nil {
 					writerConn = inbound.Conn
 					inTimer = inbound.Timer
-					if isUplink && inbound.CanSpliceCopy == 2 {
-						inbound.CanSpliceCopy = 1
-					}
-					if !isUplink && ob != nil && ob.CanSpliceCopy == 2 { // ob need to be passed in due to context can change
-						ob.CanSpliceCopy = 1
-					}
 				}
 				return proxy.CopyRawConnIfExist(ctx, conn, writerConn, writer, timer, inTimer)
 			}
 			buffer, err := reader.ReadMultiBuffer()
 			if !buffer.IsEmpty() {
-				timer.Update()
-				if isUplink && trafficState.Inbound.UplinkReaderDirectCopy || !isUplink && trafficState.Outbound.DownlinkReaderDirectCopy {
-					// XTLS Vision processes TLS-like conn's input and rawInput
-					if inputBuffer, err := buf.ReadFrom(input); err == nil && !inputBuffer.IsEmpty() {
-						buffer, _ = buf.MergeMulti(buffer, inputBuffer)
-					}
-					if rawInputBuffer, err := buf.ReadFrom(rawInput); err == nil && !rawInputBuffer.IsEmpty() {
-						buffer, _ = buf.MergeMulti(buffer, rawInputBuffer)
-					}
-					*input = bytes.Reader{} // release memory
-					input = nil
-					*rawInput = bytes.Buffer{} // release memory
-					rawInput = nil
-				}
-				if werr := writer.WriteMultiBuffer(buffer); werr != nil {
-					return werr
-				}
-			}
-			if err != nil {
-				return err
-			}
-		}
-	}()
-	if err != nil && errors.Cause(err) != io.EOF {
-		return err
-	}
-	return nil
-}
-
-// XtlsWrite filter and write xtls protocol
-func XtlsWrite(reader buf.Reader, writer buf.Writer, timer signal.ActivityUpdater, conn net.Conn, trafficState *proxy.TrafficState, ob *session.Outbound, isUplink bool, ctx context.Context) error {
-	err := func() error {
-		var ct stats.Counter
-		for {
-			buffer, err := reader.ReadMultiBuffer()
-			if isUplink && trafficState.Outbound.UplinkWriterDirectCopy || !isUplink && trafficState.Inbound.DownlinkWriterDirectCopy {
-				if inbound := session.InboundFromContext(ctx); inbound != nil {
-					if !isUplink && inbound.CanSpliceCopy == 2 {
-						inbound.CanSpliceCopy = 1
-					}
-					if isUplink && ob != nil && ob.CanSpliceCopy == 2 {
-						ob.CanSpliceCopy = 1
-					}
-				}
-				rawConn, _, writerCounter := proxy.UnwrapRawConn(conn)
-				writer = buf.NewWriter(rawConn)
-				ct = writerCounter
-				if isUplink {
-					trafficState.Outbound.UplinkWriterDirectCopy = false
-				} else {
-					trafficState.Inbound.DownlinkWriterDirectCopy = false
-				}
-			}
-			if !buffer.IsEmpty() {
-				if ct != nil {
-					ct.Add(int64(buffer.Len()))
-				}
 				timer.Update()
 				if werr := writer.WriteMultiBuffer(buffer); werr != nil {
 					return werr