fix: allow disabling ALPN by setting an empty array (#2225)

Author: eWloYW8

adapter/outbound/hysteria.go

@@ -172,7 +172,7 @@ func NewHysteria(option HysteriaOption) (*Hysteria, error) {
 		return nil, err
 	}
 
-	if len(option.ALPN) > 0 {
+	if option.ALPN != nil { // structure's Decode will ensure value not nil when input has value even it was set an empty array
 		tlsConfig.NextProtos = option.ALPN
 	} else {
 		tlsConfig.NextProtos = []string{DefaultALPN}

adapter/outbound/hysteria2.go

@@ -153,7 +153,7 @@ func NewHysteria2(option Hysteria2Option) (*Hysteria2, error) {
 		return nil, err
 	}
 
-	if len(option.ALPN) > 0 {
+	if option.ALPN != nil { // structure's Decode will ensure value not nil when input has value even it was set an empty array
 		tlsConfig.NextProtos = option.ALPN
 	}
 

adapter/outbound/trojan.go

@@ -95,7 +95,7 @@ func (t *Trojan) StreamConnContext(ctx context.Context, c net.Conn, metadata *C.
 		}
 
 		alpn := trojan.DefaultWebsocketALPN
-		if len(t.option.ALPN) != 0 {
+		if t.option.ALPN != nil { // structure's Decode will ensure value not nil when input has value even it was set an empty array
 			alpn = t.option.ALPN
 		}
 
@@ -119,7 +119,7 @@ func (t *Trojan) StreamConnContext(ctx context.Context, c net.Conn, metadata *C.
 		// default tcp network
 		// handle TLS
 		alpn := trojan.DefaultALPN
-		if len(t.option.ALPN) != 0 {
+		if t.option.ALPN != nil { // structure's Decode will ensure value not nil when input has value even it was set an empty array
 			alpn = t.option.ALPN
 		}
 		c, err = vmess.StreamTLSConn(ctx, c, &vmess.TLSConfig{