Optimization: use client session cache for TLS connection (#26)

adapters/outbound/util.go

@@ -1,10 +1,12 @@
 package adapters
 
 import (
+	"crypto/tls"
 	"fmt"
 	"net"
 	"net/http"
 	"net/url"
+	"sync"
 	"time"
 
 	C "github.com/Dreamacro/clash/constant"
@@ -14,6 +16,11 @@ const (
 	tcpTimeout = 5 * time.Second
 )
 
+var (
+	globalClientSessionCache tls.ClientSessionCache
+	once                     sync.Once
+)
+
 // DelayTest get the delay for the specified URL
 func DelayTest(proxy C.Proxy, url string) (t int16, err error) {
 	addr, err := urlToMetadata(url)
@@ -95,3 +102,10 @@ func tcpKeepAlive(c net.Conn) {
 		tcp.SetKeepAlivePeriod(30 * time.Second)
 	}
 }
+
+func getClientSessionCache() tls.ClientSessionCache {
+	once.Do(func() {
+		globalClientSessionCache = tls.NewLRUClientSessionCache(128)
+	})
+	return globalClientSessionCache
+}