Use channel for pool

https://github.com/XTLS/Xray-core/pull/5270#issuecomment-3483155727

app/proxyman/outbound/handler.go

@@ -317,8 +317,12 @@ func (h *Handler) Dial(ctx context.Context, dest net.Destination) (stat.Connecti
 	conn, err := internet.Dial(ctx, dest, h.streamSettings)
 	conn = h.getStatCouterConnection(conn)
 	outbounds := session.OutboundsFromContext(ctx)
-	ob := outbounds[len(outbounds)-1]
+	if outbounds != nil {
-	ob.Conn = conn
+		ob := outbounds[len(outbounds)-1]
+		ob.Conn = conn
+	} else {
+		// for Vision's pre-connect
+	}
 	return conn, err
 }
 

infra/conf/vless.go

@@ -212,6 +212,7 @@ type VLessOutboundConfig struct {
 	Seed       string                `json:"seed"`
 	Encryption string                `json:"encryption"`
 	Reverse    *vless.Reverse        `json:"reverse"`
+	Testpre    uint32                `json:"testpre"`
 	Vnext      []*VLessOutboundVnext `json:"vnext"`
 }
 
@@ -258,6 +259,7 @@ func (c *VLessOutboundConfig) Build() (proto.Message, error) {
 				//account.Seed = c.Seed
 				account.Encryption = c.Encryption
 				account.Reverse = c.Reverse
+				account.Testpre = c.Testpre
 			} else {
 				if err := json.Unmarshal(rawUser, account); err != nil {
 					return nil, errors.New(`VLESS users: invalid user`).Base(err)

proxy/vless/account.go

@@ -22,6 +22,7 @@ func (a *Account) AsAccount() (protocol.Account, error) {
 		Seconds:    a.Seconds,
 		Padding:    a.Padding,
 		Reverse:    a.Reverse,
+		Testpre:    a.Testpre,
 	}, nil
 }
 
@@ -38,6 +39,8 @@ type MemoryAccount struct {
 	Padding    string
 
 	Reverse *Reverse
+
+	Testpre uint32
 }
 
 // Equals implements protocol.Account.Equals().
@@ -58,5 +61,6 @@ func (a *MemoryAccount) ToProto() proto.Message {
 		Seconds:    a.Seconds,
 		Padding:    a.Padding,
 		Reverse:    a.Reverse,
+		Testpre:    a.Testpre,
 	}
 }

proxy/vless/account.pb.go

@@ -79,6 +79,7 @@ type Account struct {
 	Seconds    uint32   `protobuf:"varint,5,opt,name=seconds,proto3" json:"seconds,omitempty"`
 	Padding    string   `protobuf:"bytes,6,opt,name=padding,proto3" json:"padding,omitempty"`
 	Reverse    *Reverse `protobuf:"bytes,7,opt,name=reverse,proto3" json:"reverse,omitempty"`
+	Testpre    uint32   `protobuf:"varint,8,opt,name=testpre,proto3" json:"testpre,omitempty"`
 }
 
 func (x *Account) Reset() {
@@ -160,6 +161,13 @@ func (x *Account) GetReverse() *Reverse {
 	return nil
 }
 
+func (x *Account) GetTestpre() uint32 {
+	if x != nil {
+		return x.Testpre
+	}
+	return 0
+}
+
 var File_proxy_vless_account_proto protoreflect.FileDescriptor
 
 var file_proxy_vless_account_proto_rawDesc = []byte{
@@ -167,7 +175,7 @@ var file_proxy_vless_account_proto_rawDesc = []byte{
 	0x63, 0x6f, 0x75, 0x6e, 0x74, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x12, 0x10, 0x78, 0x72, 0x61,
 	0x79, 0x2e, 0x70, 0x72, 0x6f, 0x78, 0x79, 0x2e, 0x76, 0x6c, 0x65, 0x73, 0x73, 0x22, 0x1b, 0x0a,
 	0x07, 0x52, 0x65, 0x76, 0x65, 0x72, 0x73, 0x65, 0x12, 0x10, 0x0a, 0x03, 0x74, 0x61, 0x67, 0x18,
-	0x01, 0x20, 0x01, 0x28, 0x09, 0x52, 0x03, 0x74, 0x61, 0x67, 0x22, 0xd0, 0x01, 0x0a, 0x07, 0x41,
+	0x01, 0x20, 0x01, 0x28, 0x09, 0x52, 0x03, 0x74, 0x61, 0x67, 0x22, 0xea, 0x01, 0x0a, 0x07, 0x41,
 	0x63, 0x63, 0x6f, 0x75, 0x6e, 0x74, 0x12, 0x0e, 0x0a, 0x02, 0x69, 0x64, 0x18, 0x01, 0x20, 0x01,
 	0x28, 0x09, 0x52, 0x02, 0x69, 0x64, 0x12, 0x12, 0x0a, 0x04, 0x66, 0x6c, 0x6f, 0x77, 0x18, 0x02,
 	0x20, 0x01, 0x28, 0x09, 0x52, 0x04, 0x66, 0x6c, 0x6f, 0x77, 0x12, 0x1e, 0x0a, 0x0a, 0x65, 0x6e,
@@ -180,13 +188,15 @@ var file_proxy_vless_account_proto_rawDesc = []byte{
 	0x07, 0x70, 0x61, 0x64, 0x64, 0x69, 0x6e, 0x67, 0x12, 0x33, 0x0a, 0x07, 0x72, 0x65, 0x76, 0x65,
 	0x72, 0x73, 0x65, 0x18, 0x07, 0x20, 0x01, 0x28, 0x0b, 0x32, 0x19, 0x2e, 0x78, 0x72, 0x61, 0x79,
 	0x2e, 0x70, 0x72, 0x6f, 0x78, 0x79, 0x2e, 0x76, 0x6c, 0x65, 0x73, 0x73, 0x2e, 0x52, 0x65, 0x76,
-	0x65, 0x72, 0x73, 0x65, 0x52, 0x07, 0x72, 0x65, 0x76, 0x65, 0x72, 0x73, 0x65, 0x42, 0x52, 0x0a,
+	0x65, 0x72, 0x73, 0x65, 0x52, 0x07, 0x72, 0x65, 0x76, 0x65, 0x72, 0x73, 0x65, 0x12, 0x18, 0x0a,
-	0x14, 0x63, 0x6f, 0x6d, 0x2e, 0x78, 0x72, 0x61, 0x79, 0x2e, 0x70, 0x72, 0x6f, 0x78, 0x79, 0x2e,
+	0x07, 0x74, 0x65, 0x73, 0x74, 0x70, 0x72, 0x65, 0x18, 0x08, 0x20, 0x01, 0x28, 0x0d, 0x52, 0x07,
-	0x76, 0x6c, 0x65, 0x73, 0x73, 0x50, 0x01, 0x5a, 0x25, 0x67, 0x69, 0x74, 0x68, 0x75, 0x62, 0x2e,
+	0x74, 0x65, 0x73, 0x74, 0x70, 0x72, 0x65, 0x42, 0x52, 0x0a, 0x14, 0x63, 0x6f, 0x6d, 0x2e, 0x78,
-	0x63, 0x6f, 0x6d, 0x2f, 0x78, 0x74, 0x6c, 0x73, 0x2f, 0x78, 0x72, 0x61, 0x79, 0x2d, 0x63, 0x6f,
+	0x72, 0x61, 0x79, 0x2e, 0x70, 0x72, 0x6f, 0x78, 0x79, 0x2e, 0x76, 0x6c, 0x65, 0x73, 0x73, 0x50,
-	0x72, 0x65, 0x2f, 0x70, 0x72, 0x6f, 0x78, 0x79, 0x2f, 0x76, 0x6c, 0x65, 0x73, 0x73, 0xaa, 0x02,
+	0x01, 0x5a, 0x25, 0x67, 0x69, 0x74, 0x68, 0x75, 0x62, 0x2e, 0x63, 0x6f, 0x6d, 0x2f, 0x78, 0x74,
-	0x10, 0x58, 0x72, 0x61, 0x79, 0x2e, 0x50, 0x72, 0x6f, 0x78, 0x79, 0x2e, 0x56, 0x6c, 0x65, 0x73,
+	0x6c, 0x73, 0x2f, 0x78, 0x72, 0x61, 0x79, 0x2d, 0x63, 0x6f, 0x72, 0x65, 0x2f, 0x70, 0x72, 0x6f,
-	0x73, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
+	0x78, 0x79, 0x2f, 0x76, 0x6c, 0x65, 0x73, 0x73, 0xaa, 0x02, 0x10, 0x58, 0x72, 0x61, 0x79, 0x2e,
+	0x50, 0x72, 0x6f, 0x78, 0x79, 0x2e, 0x56, 0x6c, 0x65, 0x73, 0x73, 0x62, 0x06, 0x70, 0x72, 0x6f,
+	0x74, 0x6f, 0x33,
 }
 
 var (

proxy/vless/account.proto

@@ -22,4 +22,6 @@ message Account {
   string padding = 6;
 
   Reverse reverse = 7;
+
+  uint32 testpre = 8;
 }

proxy/vless/outbound/outbound.go

@@ -7,6 +7,7 @@ import (
 	"encoding/base64"
 	"reflect"
 	"strings"
+	"sync"
 	"time"
 	"unsafe"
 
@@ -52,6 +53,12 @@ type Handler struct {
 	cone          bool
 	encryption    *encryption.ClientInstance
 	reverse       *Reverse
+
+	testpre     uint32
+	initConns   sync.Once
+	preConns    chan stat.Connection
+	preConnWait chan struct{}
+	preConnStop chan struct{}
 }
 
 // New creates a new VLess outbound handler.
@@ -105,11 +112,20 @@ func New(ctx context.Context, config *Config) (*Handler, error) {
 		}()
 	}
 
+	handler.testpre = a.Testpre
+
 	return handler, nil
 }
 
 // Close implements common.Closable.Close().
 func (h *Handler) Close() error {
+	if h.preConnStop != nil {
+		close(h.preConnStop)
+		for range h.testpre {
+			conn := <-h.preConns
+			common.CloseIfExists(conn)
+		}
+	}
 	if h.reverse != nil {
 		return h.reverse.Close()
 	}
@@ -128,18 +144,38 @@ func (h *Handler) Process(ctx context.Context, link *transport.Link, dialer inte
 	rec := h.server
 	var conn stat.Connection
 
-	if err := retry.ExponentialBackoff(5, 200).On(func() error {
+	if h.testpre > 0 && h.reverse == nil {
-		var err error
+		h.initConns.Do(func() {
-		conn, err = dialer.Dial(ctx, rec.Destination)
+			h.preConns = make(chan stat.Connection, h.testpre)
-		if err != nil {
+			h.preConnStop = make(chan struct{})
-			return err
+			go h.preConnWorker(dialer, rec.Destination)
+		})
+		select {
+		case h.preConnWait <- struct{}{}:
+		default:
+		}
+		select {
+		case conn = <-h.preConns:
+		default:
+		}
+	}
+
+	if conn == nil {
+		if err := retry.ExponentialBackoff(5, 200).On(func() error {
+			var err error
+			conn, err = dialer.Dial(ctx, rec.Destination)
+			if err != nil {
+				return err
+			}
+			return nil
+		}); err != nil {
+			return errors.New("failed to find an available destination").Base(err).AtWarning()
 		}
-		return nil
-	}); err != nil {
-		return errors.New("failed to find an available destination").Base(err).AtWarning()
 	}
 	defer conn.Close()
 
+	ob.Conn = conn // for Vision's pre-connect
+
 	iConn := conn
 	if statConn, ok := iConn.(*stat.CounterConnection); ok {
 		iConn = statConn.Connection
@@ -426,3 +462,51 @@ func (r *Reverse) Start() error {
 func (r *Reverse) Close() error {
 	return r.monitorTask.Close()
 }
+
+func (h *Handler) preConnWorker(dialer internet.Dialer, dest net.Destination) {
+	// conn in conns may be nil
+	conns := make(chan stat.Connection)
+	dial := func() {
+		conn, err := dialer.Dial(context.Background(), dest)
+		if err != nil {
+			errors.LogError(context.Background(), "failed to dial VLESS pre connection: ", err)
+			common.CloseIfExists(conn)
+		}
+		conns <- conn
+	}
+	go func() {
+		go dial() // get a conn immediately
+		for range h.testpre - 1 {
+			select {
+			case <-h.preConnWait:
+				go dial()
+			case <-h.preConnStop:
+				return
+			}
+		}
+	}()
+	for {
+		select {
+		case conn := <-conns:
+			if conn != nil {
+				select {
+				case h.preConns <- conn:
+				case <-h.preConnStop:
+					common.CloseIfExists(conn)
+					return
+				}
+				go dial()
+			} else {
+				// sleep until next client try if dial failed
+				select {
+				case <-h.preConnWait:
+					go dial()
+				case <-h.preConnStop:
+					return
+				}
+			}
+		case <-h.preConnStop:
+			return
+		}
+	}
+}