chore: simplify fast open code

common/net/earlyconn.go

@@ -0,0 +1,67 @@
+package net
+
+import (
+	"net"
+	"sync"
+	"sync/atomic"
+	"unsafe"
+
+	"github.com/metacubex/mihomo/common/buf"
+)
+
+type earlyConn struct {
+	ExtendedConn // only expose standard N.ExtendedConn function to outside
+	resFunc      func() error
+	resOnce      sync.Once
+	resErr       error
+}
+
+func (conn *earlyConn) Response() error {
+	conn.resOnce.Do(func() {
+		conn.resErr = conn.resFunc()
+	})
+	return conn.resErr
+}
+
+func (conn *earlyConn) Read(b []byte) (n int, err error) {
+	err = conn.Response()
+	if err != nil {
+		return 0, err
+	}
+	return conn.ExtendedConn.Read(b)
+}
+
+func (conn *earlyConn) ReadBuffer(buffer *buf.Buffer) (err error) {
+	err = conn.Response()
+	if err != nil {
+		return err
+	}
+	return conn.ExtendedConn.ReadBuffer(buffer)
+}
+
+func (conn *earlyConn) Upstream() any {
+	return conn.ExtendedConn
+}
+
+func (conn *earlyConn) Success() bool {
+	// atomic visit sync.Once.done
+	return atomic.LoadUint32((*uint32)(unsafe.Pointer(&conn.resOnce))) == 1 && conn.resErr == nil
+}
+
+func (conn *earlyConn) ReaderReplaceable() bool {
+	return conn.Success()
+}
+
+func (conn *earlyConn) ReaderPossiblyReplaceable() bool {
+	return !conn.Success()
+}
+
+func (conn *earlyConn) WriterReplaceable() bool {
+	return true
+}
+
+var _ ExtendedConn = (*earlyConn)(nil)
+
+func NewEarlyConn(c net.Conn, f func() error) net.Conn {
+	return &earlyConn{ExtendedConn: NewExtendedConn(c), resFunc: f}
+}