Fix: http proxy Upgrade behavior (#2097)

common/net/relay.go

@@ -0,0 +1,30 @@
+package net
+
+import (
+	"io"
+	"net"
+	"time"
+
+	"github.com/Dreamacro/clash/common/pool"
+)
+
+// Relay copies between left and right bidirectionally.
+func Relay(leftConn, rightConn net.Conn) {
+	ch := make(chan error)
+
+	go func() {
+		buf := pool.Get(pool.RelayBufferSize)
+		// Wrapping to avoid using *net.TCPConn.(ReadFrom)
+		// See also https://github.com/Dreamacro/clash/pull/1209
+		_, err := io.CopyBuffer(WriteOnlyWriter{Writer: leftConn}, ReadOnlyReader{Reader: rightConn}, buf)
+		pool.Put(buf)
+		leftConn.SetReadDeadline(time.Now())
+		ch <- err
+	}()
+
+	buf := pool.Get(pool.RelayBufferSize)
+	io.CopyBuffer(WriteOnlyWriter{Writer: rightConn}, ReadOnlyReader{Reader: leftConn}, buf)
+	pool.Put(buf)
+	rightConn.SetReadDeadline(time.Now())
+	<-ch
+}