use external config converter first, and then fallback to the internal one

main/config_json.go

@@ -1,5 +1,41 @@
-// +build json
-
 package main
 
-import _ "v2ray.com/core/tools/conf"
+import (
+	"io"
+	"os"
+	"os/exec"
+
+	"v2ray.com/core"
+	"v2ray.com/core/app/log"
+	"v2ray.com/core/common/platform"
+	jsonconf "v2ray.com/ext/tools/conf/serial"
+)
+
+func jsonToProto(input io.Reader) (*core.Config, error) {
+	v2ctl := platform.GetToolLocation("v2ctl")
+	_, err := os.Stat(v2ctl)
+	if err != nil {
+		return nil, err
+	}
+	cmd := exec.Command(v2ctl, "config")
+	cmd.Stdin = input
+	cmd.Stderr = os.Stderr
+
+	stdoutReader, err := cmd.StdoutPipe()
+	if err != nil {
+		return nil, err
+	}
+	defer stdoutReader.Close()
+	return core.LoadConfig(core.ConfigFormat_Protobuf, stdoutReader)
+}
+
+func init() {
+	core.RegisterConfigLoader(core.ConfigFormat_JSON, func(input io.Reader) (*core.Config, error) {
+		config, err := jsonToProto(input)
+		if err != nil {
+			log.Trace(newError("failed to execute v2ctl to convert config file.").Base(err).AtWarning())
+			return jsonconf.LoadJSONConfig(input)
+		}
+		return config, nil
+	})
+}