Feature: support relay (proxy chains) (#539)

adapters/outboundgroup/fallback.go

@@ -77,7 +77,7 @@ func (f *Fallback) findAliveProxy() C.Proxy {
 
 func NewFallback(name string, providers []provider.ProxyProvider) *Fallback {
 	return &Fallback{
-		Base:      outbound.NewBase(name, C.Fallback, false),
+		Base:      outbound.NewBase(name, "", C.Fallback, false),
 		single:    singledo.NewSingle(defaultGetProxiesDuration),
 		providers: providers,
 	}

adapters/outboundgroup/loadbalance.go

@@ -120,7 +120,7 @@ func (lb *LoadBalance) MarshalJSON() ([]byte, error) {
 
 func NewLoadBalance(name string, providers []provider.ProxyProvider) *LoadBalance {
 	return &LoadBalance{
-		Base:      outbound.NewBase(name, C.LoadBalance, false),
+		Base:      outbound.NewBase(name, "", C.LoadBalance, false),
 		single:    singledo.NewSingle(defaultGetProxiesDuration),
 		maxRetry:  3,
 		providers: providers,

adapters/outboundgroup/parser.go

@@ -64,7 +64,7 @@ func ParseProxyGroup(config map[string]interface{}, proxyMap map[string]C.Proxy,
 			providers = append(providers, pd)
 		} else {
 			// select don't need health check
-			if groupOption.Type == "select" {
+			if groupOption.Type == "select" || groupOption.Type == "relay" {
 				hc := provider.NewHealthCheck(ps, "", 0)
 				pd, err := provider.NewCompatibleProvider(groupName, ps, hc)
 				if err != nil {
@@ -108,6 +108,8 @@ func ParseProxyGroup(config map[string]interface{}, proxyMap map[string]C.Proxy,
 		group = NewFallback(groupName, providers)
 	case "load-balance":
 		group = NewLoadBalance(groupName, providers)
+	case "relay":
+		group = NewRelay(groupName, providers)
 	default:
 		return nil, fmt.Errorf("%w: %s", errType, groupOption.Type)
 	}

adapters/outboundgroup/relay.go

@@ -0,0 +1,84 @@
+package outboundgroup
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+
+	"github.com/Dreamacro/clash/adapters/outbound"
+	"github.com/Dreamacro/clash/adapters/provider"
+	"github.com/Dreamacro/clash/common/singledo"
+	"github.com/Dreamacro/clash/component/dialer"
+	C "github.com/Dreamacro/clash/constant"
+)
+
+type Relay struct {
+	*outbound.Base
+	single    *singledo.Single
+	providers []provider.ProxyProvider
+}
+
+func (r *Relay) DialContext(ctx context.Context, metadata *C.Metadata) (C.Conn, error) {
+	proxies := r.proxies()
+	if len(proxies) == 0 {
+		return nil, errors.New("Proxy does not exist")
+	}
+	first := proxies[0]
+	last := proxies[len(proxies)-1]
+
+	c, err := dialer.DialContext(ctx, "tcp", first.Addr())
+	if err != nil {
+		return nil, fmt.Errorf("%s connect error: %w", first.Addr(), err)
+	}
+	tcpKeepAlive(c)
+
+	var currentMeta *C.Metadata
+	for _, proxy := range proxies[1:] {
+		currentMeta, err = addrToMetadata(proxy.Addr())
+		if err != nil {
+			return nil, err
+		}
+
+		c, err = first.StreamConn(c, currentMeta)
+		if err != nil {
+			return nil, fmt.Errorf("%s connect error: %w", first.Addr(), err)
+		}
+
+		first = proxy
+	}
+
+	c, err = last.StreamConn(c, metadata)
+	if err != nil {
+		return nil, fmt.Errorf("%s connect error: %w", last.Addr(), err)
+	}
+
+	return outbound.NewConn(c, r), nil
+}
+
+func (r *Relay) MarshalJSON() ([]byte, error) {
+	var all []string
+	for _, proxy := range r.proxies() {
+		all = append(all, proxy.Name())
+	}
+	return json.Marshal(map[string]interface{}{
+		"type": r.Type().String(),
+		"all":  all,
+	})
+}
+
+func (r *Relay) proxies() []C.Proxy {
+	elm, _, _ := r.single.Do(func() (interface{}, error) {
+		return getProvidersProxies(r.providers), nil
+	})
+
+	return elm.([]C.Proxy)
+}
+
+func NewRelay(name string, providers []provider.ProxyProvider) *Relay {
+	return &Relay{
+		Base:      outbound.NewBase(name, "", C.Relay, false),
+		single:    singledo.NewSingle(defaultGetProxiesDuration),
+		providers: providers,
+	}
+}

adapters/outboundgroup/selector.go

@@ -77,7 +77,7 @@ func (s *Selector) proxies() []C.Proxy {
 func NewSelector(name string, providers []provider.ProxyProvider) *Selector {
 	selected := providers[0].Proxies()[0]
 	return &Selector{
-		Base:      outbound.NewBase(name, C.Selector, false),
+		Base:      outbound.NewBase(name, "", C.Selector, false),
 		single:    singledo.NewSingle(defaultGetProxiesDuration),
 		providers: providers,
 		selected:  selected,

adapters/outboundgroup/urltest.go

@@ -86,7 +86,7 @@ func (u *URLTest) MarshalJSON() ([]byte, error) {
 
 func NewURLTest(name string, providers []provider.ProxyProvider) *URLTest {
 	return &URLTest{
-		Base:       outbound.NewBase(name, C.URLTest, false),
+		Base:       outbound.NewBase(name, "", C.URLTest, false),
 		single:     singledo.NewSingle(defaultGetProxiesDuration),
 		fastSingle: singledo.NewSingle(time.Second * 10),
 		providers:  providers,

adapters/outboundgroup/util.go

@@ -0,0 +1,53 @@
+package outboundgroup
+
+import (
+	"fmt"
+	"net"
+	"time"
+
+	C "github.com/Dreamacro/clash/constant"
+)
+
+func addrToMetadata(rawAddress string) (addr *C.Metadata, err error) {
+	host, port, err := net.SplitHostPort(rawAddress)
+	if err != nil {
+		err = fmt.Errorf("addrToMetadata failed: %w", err)
+		return
+	}
+
+	ip := net.ParseIP(host)
+	if ip != nil {
+		if ip.To4() != nil {
+			addr = &C.Metadata{
+				AddrType: C.AtypIPv4,
+				Host:     "",
+				DstIP:    ip,
+				DstPort:  port,
+			}
+			return
+		} else {
+			addr = &C.Metadata{
+				AddrType: C.AtypIPv6,
+				Host:     "",
+				DstIP:    ip,
+				DstPort:  port,
+			}
+			return
+		}
+	} else {
+		addr = &C.Metadata{
+			AddrType: C.AtypDomainName,
+			Host:     host,
+			DstIP:    nil,
+			DstPort:  port,
+		}
+		return
+	}
+}
+
+func tcpKeepAlive(c net.Conn) {
+	if tcp, ok := c.(*net.TCPConn); ok {
+		tcp.SetKeepAlive(true)
+		tcp.SetKeepAlivePeriod(30 * time.Second)
+	}
+}