protocol: add v2 wire protocol with binary framing and capability negotiation (#5294)

server/proxy/proxy.go

@@ -44,7 +44,26 @@ func RegisterProxyFactory(proxyConfType reflect.Type, factory func(*BaseProxy) P
 	proxyFactoryRegistry[proxyConfType] = factory
 }
 
-type GetWorkConnFn func() (net.Conn, error)
+type WorkConn struct {
+	conn *msg.Conn
+}
+
+func NewWorkConn(conn *msg.Conn) *WorkConn {
+	return &WorkConn{conn: conn}
+}
+
+func (c *WorkConn) Start(m *msg.StartWorkConn) (net.Conn, error) {
+	if err := c.conn.WriteMsg(m); err != nil {
+		return nil, err
+	}
+	return c.conn, nil
+}
+
+func (c *WorkConn) Close() error {
+	return c.conn.Close()
+}
+
+type GetWorkConnFn func() (*WorkConn, error)
 
 type Proxy interface {
 	Context() context.Context
@@ -125,13 +144,13 @@ func (pxy *BaseProxy) GetWorkConnFromPool(src, dst net.Addr) (workConn net.Conn,
 	xl := xlog.FromContextSafe(pxy.ctx)
 	// try all connections from the pool
 	for i := 0; i < pxy.poolCount+1; i++ {
-		if workConn, err = pxy.getWorkConnFn(); err != nil {
+		var pxyWorkConn *WorkConn
+		if pxyWorkConn, err = pxy.getWorkConnFn(); err != nil {
 			xl.Warnf("failed to get work connection: %v", err)
 			return
 		}
-		xl.Debugf("get a new work connection: [%s]", workConn.RemoteAddr().String())
+		xl.Debugf("get a new work connection: [%s]", pxyWorkConn.conn.RemoteAddr().String())
 		xl.Spawn().AppendPrefix(pxy.GetName())
-		workConn = netpkg.NewContextConn(pxy.ctx, workConn)
 
 		var (
 			srcAddr    string
@@ -150,7 +169,7 @@ func (pxy *BaseProxy) GetWorkConnFromPool(src, dst net.Addr) (workConn net.Conn,
 			dstAddr, dstPortStr, _ = net.SplitHostPort(dst.String())
 			dstPort, _ = strconv.ParseUint(dstPortStr, 10, 16)
 		}
-		err = msg.WriteMsg(workConn, &msg.StartWorkConn{
+		workConn, err = pxyWorkConn.Start(&msg.StartWorkConn{
 			ProxyName: pxy.GetName(),
 			SrcAddr:   srcAddr,
 			SrcPort:   uint16(srcPort),
@@ -160,9 +179,10 @@ func (pxy *BaseProxy) GetWorkConnFromPool(src, dst net.Addr) (workConn net.Conn,
 		})
 		if err != nil {
 			xl.Warnf("failed to send message to work connection from pool: %v, times: %d", err, i)
-			workConn.Close()
+			pxyWorkConn.Close()
 			workConn = nil
 		} else {
+			workConn = netpkg.NewContextConn(pxy.ctx, workConn)
 			break
 		}
 	}

server/proxy/proxy_test.go

@@ -0,0 +1,53 @@
+// Copyright 2026 The frp Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package proxy
+
+import (
+	"net"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/fatedier/frp/pkg/msg"
+)
+
+func TestWorkConnStartWritesStartWorkConn(t *testing.T) {
+	client, server := net.Pipe()
+	defer client.Close()
+	defer server.Close()
+
+	serverMsgConn := msg.NewConn(server, msg.NewV2ReadWriter(server))
+	clientMsgConn := msg.NewConn(client, msg.NewV2ReadWriter(client))
+	workConn := NewWorkConn(serverMsgConn)
+
+	in := &msg.StartWorkConn{ProxyName: "tcp", SrcAddr: "127.0.0.1", SrcPort: 1234}
+	type startResult struct {
+		conn net.Conn
+		err  error
+	}
+	resultCh := make(chan startResult, 1)
+	go func() {
+		conn, err := workConn.Start(in)
+		resultCh <- startResult{conn: conn, err: err}
+	}()
+
+	out, err := clientMsgConn.ReadMsg()
+	require.NoError(t, err)
+	require.Equal(t, in, out)
+
+	result := <-resultCh
+	require.NoError(t, result.err)
+	require.Same(t, serverMsgConn, result.conn)
+}