diff --git a/include/dnsproxy.h b/include/dnsproxy.h
index 261db00..baa3750 100644
--- a/include/dnsproxy.h
+++ b/include/dnsproxy.h
@@ -15,14 +15,9 @@ typedef struct {
 } dnsproxy;
 
 dnsproxy* dnsproxy_init(int port);
-void dnsproxy_dump(char *caption, dnsproxy *info);
-
-void dnsproxy_add_primary(dnsproxy *info, char *server);
-void dnsproxy_add_fallback(dnsproxy *info, char *server);
-void dnsproxy_add_bootstrap(dnsproxy *info, char *server);
-
-char* dnsproxy_gen_config(dnsproxy *info);
-
-process* dnsproxy_load(char *caption, dnsproxy *info, char *work_dir, char *file);
+void dnsproxy_add_primary(dnsproxy *info, const char *server);
+void dnsproxy_add_fallback(dnsproxy *info, const char *server);
+void dnsproxy_add_bootstrap(dnsproxy *info, const char *server);
+process* dnsproxy_load(const char *caption, dnsproxy *info, const char *file);
 
 #endif
diff --git a/include/utils/str.h b/include/utils/str.h
index 94ae2b5..81f8384 100644
--- a/include/utils/str.h
+++ b/include/utils/str.h
@@ -1,12 +1,12 @@
 #ifndef _STR_H_
 #define _STR_H_
 
-char* string_init(char *str);
-char* string_join(char *base, const char *add, int is_new);
+char* string_init(const char *str);
+char* string_join(const char *base, const char *add);
 
 char** string_list_init();
 int string_list_len(char **string_list);
 char* string_list_dump(char **string_list);
-char** string_list_append(char **string_list, char *string);
+char** string_list_append(char **string_list, const char *string);
 
 #endif
diff --git a/src/cleardns.c b/src/cleardns.c
index ccabe72..5dc19aa 100644
--- a/src/cleardns.c
+++ b/src/cleardns.c
@@ -1,7 +1,6 @@
 #include "logger.h"
 #include "common.h"
 #include "dnsproxy.h"
-
 #include "str.h"
 
 //#include <stdio.h>
@@ -31,7 +30,6 @@
 int main(int argc, char *argv[]) { // ClearDNS server
 
     LOG_LEVEL = LOG_DEBUG;
-
     log_info("ClearDNS server start (%s)", VERSION);
 
     dnsproxy *domestic = dnsproxy_init(DOMESTIC_PORT);
@@ -47,18 +45,13 @@ int main(int argc, char *argv[]) { // ClearDNS server
 
 //    domestic->verify = FALSE;
 //    domestic->parallel = FALSE;
-//    domestic->optimistic = TRUE;
-    domestic->cache = 0;
-
-    dnsproxy_dump("Domestic", domestic);
-
-//    char *config = dnsproxy_gen_config(domestic);
-//    log_info("\n%s", config);
-
-//    log_info("%s", string_join(WORK_DIR, "domestic.json", TRUE));
+    domestic->optimistic = TRUE;
+//    domestic->cache = 0;
 
-    process *p = dnsproxy_load("Domestic", domestic, WORK_DIR, "domestic.json");
-    log_info("%s", string_list_dump(p->cmd));
+    process *p = dnsproxy_load("Domestic", domestic, "domestic.json");
+    log_info("cmd -> %s", string_list_dump(p->cmd));
+    log_info("env -> %s", string_list_dump(p->env));
+    log_info("cwd -> %s", p->cwd);
 
 //    int debug_mode = 0;
 //    fprintf(stderr, "[ClearDNS] Server start.\n");
diff --git a/src/dnsproxy.c b/src/dnsproxy.c
index 64d80cd..e5967a7 100644
--- a/src/dnsproxy.c
+++ b/src/dnsproxy.c
@@ -6,7 +6,22 @@
 #include "common.h"
 #include "cJSON.h"
 
-dnsproxy* dnsproxy_init(int port) {
+char* dnsproxy_gen_config(dnsproxy *info);
+void dnsproxy_dump(const char *caption, dnsproxy *info);
+
+void dnsproxy_add_primary(dnsproxy *info, const char *server) { // add primary dns server
+    info->primary = string_list_append(info->primary, server);
+}
+
+void dnsproxy_add_fallback(dnsproxy *info, const char *server) { // add fallback dns server
+    info->fallback = string_list_append(info->fallback, server);
+}
+
+void dnsproxy_add_bootstrap(dnsproxy *info, const char *server) { // add bootstrap dns server
+    info->bootstrap = string_list_append(info->bootstrap, server);
+}
+
+dnsproxy* dnsproxy_init(int port) { // init dnsproxy options
     dnsproxy *info = (dnsproxy*)malloc(sizeof(dnsproxy));
     info->port = port;
     info->verify = TRUE;
@@ -19,7 +34,7 @@ dnsproxy* dnsproxy_init(int port) {
     return info;
 }
 
-void dnsproxy_dump(char *caption, dnsproxy *info) {
+void dnsproxy_dump(const char *caption, dnsproxy *info) { // show dnsproxy info in debug log
     log_debug("%s listen port -> %d", caption, info->port);
     log_debug("%s verify -> %s", caption, show_bool(info->verify));
     log_debug("%s parallel -> %s", caption, show_bool(info->parallel));
@@ -30,70 +45,63 @@ void dnsproxy_dump(char *caption, dnsproxy *info) {
     log_debug("%s cache -> %d", caption, info->cache);
 }
 
-void dnsproxy_add_primary(dnsproxy *info, char *server) {
-    info->primary = string_list_append(info->primary, server);
-}
+process* dnsproxy_load(const char *caption, dnsproxy *info, const char *file) {
+    dnsproxy_dump(caption, info);
+    char *config = dnsproxy_gen_config(info); // string config (JSON format)
+    char *config_file = string_join(WORK_DIR, file);
+    save_file(config_file, config);
+    free(config_file);
+    free(config);
 
-void dnsproxy_add_fallback(dnsproxy *info, char *server) {
-    info->fallback = string_list_append(info->fallback, server);
-}
-
-void dnsproxy_add_bootstrap(dnsproxy *info, char *server) {
-    info->bootstrap = string_list_append(info->bootstrap, server);
+    char *option = string_join("--config-path=", file);
+    process *p = (process*)malloc(sizeof(process));
+    p->cmd = command_init(DNSPROXY_BIN);
+    p->cmd = string_list_append(p->cmd, option);
+    p->env = string_list_init();
+    p->cwd = WORK_DIR;
+    free(option);
+    return p;
 }
 
-char* dnsproxy_gen_config(dnsproxy *info) {
+char* dnsproxy_gen_config(dnsproxy *info) { // generate json configure from dnsproxy options
     cJSON *config = cJSON_CreateObject();
     if (!info->verify) {
         cJSON_AddTrueToObject(config, "insecure"); // insecure --(default)--> `false`
     }
     if (info->parallel) {
-        cJSON_AddTrueToObject(config, "all-servers");
+        cJSON_AddTrueToObject(config, "all-servers"); // all-servers --(default)--> `false`
     }
     if (info->cache) {
-        cJSON_AddTrueToObject(config, "cache");
+        cJSON_AddTrueToObject(config, "cache"); // cache --(default)--> `false`
         cJSON_AddNumberToObject(config, "cache-size", info->cache);
     }
     if (info->optimistic) {
-        cJSON_AddTrueToObject(config, "cache-optimistic");
+        cJSON_AddTrueToObject(config, "cache-optimistic"); // cache-optimistic --(default)--> `false`
     }
 
     cJSON *port = cJSON_CreateArray();
     cJSON_AddItemToArray(port, cJSON_CreateNumber(info->port));
-    cJSON_AddItemToObject(config, "listen-ports", port);
+    cJSON_AddItemToObject(config, "listen-ports", port); // listen-ports <=> port
 
     cJSON *bootstrap = cJSON_CreateArray();
     for (char **server = info->bootstrap; *server != NULL; ++server) {
         cJSON_AddItemToArray(bootstrap, cJSON_CreateString(*server));
     }
-    cJSON_AddItemToObject(config, "bootstrap", bootstrap);
+    cJSON_AddItemToObject(config, "bootstrap", bootstrap); // bootstrap <=> bootstrap
 
     cJSON *fallback = cJSON_CreateArray();
     for (char **server = info->fallback; *server != NULL; ++server) {
         cJSON_AddItemToArray(fallback, cJSON_CreateString(*server));
     }
-    cJSON_AddItemToObject(config, "fallback", fallback);
+    cJSON_AddItemToObject(config, "fallback", fallback); // fallback <=> fallback
 
     cJSON *primary = cJSON_CreateArray();
     for (char **server = info->primary; *server != NULL; ++server) {
         cJSON_AddItemToArray(primary, cJSON_CreateString(*server));
     }
-    cJSON_AddItemToObject(config, "upstream", primary);
+    cJSON_AddItemToObject(config, "upstream", primary); // upstream <=> primary
 
     char *config_str = cJSON_Print(config);
-    cJSON_Delete(config);
+    cJSON_Delete(config); // free json object
     return config_str;
 }
-
-process* dnsproxy_load(char *caption, dnsproxy *info, char *work_dir, char *file) {
-    char *config = dnsproxy_gen_config(info);
-
-    save_file(string_join(work_dir, file, TRUE), config);
-
-    process *demo = (process*)malloc(sizeof(process));
-    demo->cmd = command_init(DNSPROXY_BIN);
-    demo->env = string_list_init();
-    demo->cwd = work_dir;
-
-    return demo;
-}
diff --git a/src/utils/str.c b/src/utils/str.c
index 936fe76..6a8c30e 100644
--- a/src/utils/str.c
+++ b/src/utils/str.c
@@ -2,19 +2,25 @@
 #include <string.h>
 #include "str.h"
 
-char* string_init(char *str) {
+char* string_init(const char *str) {
     return strcpy((char*)malloc(strlen(str) + 1), str);
 }
 
-char* string_join(char *base, const char *add, int is_new) {
-    unsigned long string_len = strlen(base) + strlen(add);
-    if (is_new) {
-        char *ret = (char*)malloc(sizeof(char) * (string_len + 1));
-        return strcat(strcpy(ret, base), add);
-    } else {
-        base = (char*)realloc(base, sizeof(char) * (string_len + 1));
-        return strcat(base, add);
-    }
+char* string_join(const char *base, const char *add) {
+    char *ret = (char*)malloc(sizeof(char) * (strlen(base) + strlen(add) + 1));
+    return strcat(strcpy(ret, base), add);
+}
+
+char** string_list_init() {
+    char **string_list = (char**)malloc(sizeof(char*));
+    *string_list = NULL;
+    return string_list;
+}
+
+int string_list_len(char **string_list) {
+    int num = 0;
+    while(string_list[num++] != NULL); // get string list size
+    return num - 1;
 }
 
 char* string_list_dump(char **string_list) { // ['a', 'b', 'c', ...]
@@ -37,19 +43,7 @@ char* string_list_dump(char **string_list) { // ['a', 'b', 'c', ...]
     return string_ret;
 }
 
-int string_list_len(char **string_list) {
-    int num = 0;
-    while(string_list[num++] != NULL); // get string list size
-    return num - 1;
-}
-
-char** string_list_init() {
-    char **string_list = (char**)malloc(sizeof(char*));
-    *string_list = NULL;
-    return string_list;
-}
-
-char** string_list_append(char **string_list, char *string) {
+char** string_list_append(char **string_list, const char *string) {
     int len = string_list_len(string_list);
     string_list = (char**)realloc(string_list, sizeof(char*) * (len + 2));
     string_list[len] = string_init(string);