chore: support v2ray http upgrade server too

common/net/cached.go

@@ -0,0 +1,49 @@
+package net
+
+import (
+	"net"
+
+	"github.com/Dreamacro/clash/common/buf"
+)
+
+var _ ExtendedConn = (*CachedConn)(nil)
+
+type CachedConn struct {
+	ExtendedConn
+	data []byte
+}
+
+func NewCachedConn(c net.Conn, data []byte) *CachedConn {
+	return &CachedConn{NewExtendedConn(c), data}
+}
+
+func (c *CachedConn) Read(b []byte) (n int, err error) {
+	if len(c.data) > 0 {
+		n = copy(b, c.data)
+		c.data = c.data[n:]
+		return
+	}
+	return c.ExtendedConn.Read(b)
+}
+
+func (c *CachedConn) ReadCached() *buf.Buffer { // call in sing/common/bufio.Copy
+	if len(c.data) > 0 {
+		return buf.As(c.data)
+	}
+	return nil
+}
+
+func (c *CachedConn) Upstream() any {
+	return c.ExtendedConn
+}
+
+func (c *CachedConn) ReaderReplaceable() bool {
+	if len(c.data) > 0 {
+		return false
+	}
+	return true
+}
+
+func (c *CachedConn) WriterReplaceable() bool {
+	return true
+}