Improve: Dial would reset proxy alive status

adapters/outbound/base.go

@@ -2,6 +2,9 @@ package adapters
 
 import (
 	"encoding/json"
+	"net"
+	"net/http"
+	"time"
 
 	C "github.com/Dreamacro/clash/constant"
 )
@@ -19,8 +22,62 @@ func (b *Base) Type() C.AdapterType {
 	return b.tp
 }
 
+func (b *Base) Destroy() {}
+
 func (b *Base) MarshalJSON() ([]byte, error) {
 	return json.Marshal(map[string]string{
 		"type": b.Type().String(),
 	})
 }
+
+type Proxy struct {
+	C.ProxyAdapter
+	alive bool
+}
+
+func (p *Proxy) Alive() bool {
+	return p.alive
+}
+
+func (p *Proxy) Dial(metadata *C.Metadata) (net.Conn, error) {
+	conn, err := p.ProxyAdapter.Dial(metadata)
+	p.alive = err == nil
+	return conn, err
+}
+
+// URLTest get the delay for the specified URL
+func (p *Proxy) URLTest(url string) (t int16, err error) {
+	addr, err := urlToMetadata(url)
+	if err != nil {
+		return
+	}
+
+	start := time.Now()
+	instance, err := p.ProxyAdapter.Dial(&addr)
+	if err != nil {
+		return
+	}
+	defer instance.Close()
+	transport := &http.Transport{
+		Dial: func(string, string) (net.Conn, error) {
+			return instance, nil
+		},
+		// from http.DefaultTransport
+		MaxIdleConns:          100,
+		IdleConnTimeout:       90 * time.Second,
+		TLSHandshakeTimeout:   10 * time.Second,
+		ExpectContinueTimeout: 1 * time.Second,
+	}
+	client := http.Client{Transport: transport}
+	resp, err := client.Get(url)
+	if err != nil {
+		return
+	}
+	resp.Body.Close()
+	t = int16(time.Since(start) / time.Millisecond)
+	return
+}
+
+func NewProxy(adapter C.ProxyAdapter) *Proxy {
+	return &Proxy{adapter, true}
+}