diff --git a/include/applet/dnsproxy.h b/include/applet/dnsproxy.h
index b112689..81a26e7 100644
--- a/include/applet/dnsproxy.h
+++ b/include/applet/dnsproxy.h
@@ -20,8 +20,4 @@ void dnsproxy_free(dnsproxy *info);
 dnsproxy* dnsproxy_init(uint16_t port);
 process* dnsproxy_load(const char *caption, dnsproxy *info, const 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);
-
 #endif
diff --git a/include/common/sundry.h b/include/common/sundry.h
index c10542d..f12a2a5 100644
--- a/include/common/sundry.h
+++ b/include/common/sundry.h
@@ -4,7 +4,7 @@
 #include <stdint.h>
 
 char* show_bool(uint8_t value);
-char* string_init(const char *str);
+char* string_load(const char *fmt, ...);
 char* uint32_to_string(uint32_t number);
 char* string_join(const char *base, const char *add);
 void string_list_debug(char *describe, char **string_list);
diff --git a/src/applet/adguard.c b/src/applet/adguard.c
index 9deaa3a..328d114 100644
--- a/src/applet/adguard.c
+++ b/src/applet/adguard.c
@@ -25,8 +25,8 @@ adguard* adguard_init() { // init adguard options
     info->dns_port = DNS_PORT;
     info->web_port = ADGUARD_PORT;
     info->upstream = string_join("127.0.0.1:", port_str); // default upstream
-    info->username = string_init(ADGUARD_USER);
-    info->password = string_init(ADGUARD_PASSWD);
+    info->username = strdup(ADGUARD_USER);
+    info->password = strdup(ADGUARD_PASSWD);
     free(port_str);
     return info;
 }
diff --git a/src/applet/crontab.c b/src/applet/crontab.c
index 515f1c5..126d1f0 100644
--- a/src/applet/crontab.c
+++ b/src/applet/crontab.c
@@ -1,4 +1,5 @@
 #include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
 #include "logger.h"
 #include "sundry.h"
@@ -17,7 +18,7 @@ void crontab_free(crontab *info) { // free crontab options
 crontab* crontab_init() { // init crontab options
     crontab *info = (crontab *)malloc(sizeof(crontab));
     info->debug = FALSE;
-    info->cron = string_init(UPDATE_CRON);
+    info->cron = strdup(UPDATE_CRON);
     return info;
 }
 
diff --git a/src/applet/dnsproxy.c b/src/applet/dnsproxy.c
index ca2f480..593b4b2 100644
--- a/src/applet/dnsproxy.c
+++ b/src/applet/dnsproxy.c
@@ -10,18 +10,6 @@
 char* dnsproxy_config(dnsproxy *info);
 void dnsproxy_dump(const char *caption, dnsproxy *info);
 
-void dnsproxy_add_primary(dnsproxy *info, const char *server) { // add primary dns server
-    string_list_append(&info->primary, server);
-}
-
-void dnsproxy_add_fallback(dnsproxy *info, const char *server) { // add fallback dns server
-    string_list_append(&info->fallback, server);
-}
-
-void dnsproxy_add_bootstrap(dnsproxy *info, const char *server) { // add bootstrap dns server
-    string_list_append(&info->bootstrap, server);
-}
-
 void dnsproxy_free(dnsproxy *info) { // free dnsproxy options
     string_list_free(info->bootstrap);
     string_list_free(info->fallback);
diff --git a/src/applet/overture.c b/src/applet/overture.c
index 393478e..f9024b8 100644
--- a/src/applet/overture.c
+++ b/src/applet/overture.c
@@ -1,4 +1,5 @@
 #include <stdlib.h>
+#include <string.h>
 #include "cJSON.h"
 #include "logger.h"
 #include "sundry.h"
@@ -30,10 +31,10 @@ overture* overture_init() { // init overture options
     info->foreign_port = FOREIGN_PORT;
     info->domestic_port = DOMESTIC_PORT;
     info->reject_type = uint32_list_init();
-    info->foreign_ip_file = string_init("/dev/null");
-    info->domestic_ip_file = string_init("/dev/null");
-    info->foreign_domain_file = string_init("/dev/null");
-    info->domestic_domain_file = string_init("/dev/null");
+    info->foreign_ip_file = strdup("/dev/null");
+    info->domestic_ip_file = strdup("/dev/null");
+    info->foreign_domain_file = strdup("/dev/null");
+    info->domestic_domain_file = strdup("/dev/null");
     return info;
 }
 
diff --git a/src/cleardns.c b/src/cleardns.c
index 8ca9c17..3ad366a 100644
--- a/src/cleardns.c
+++ b/src/cleardns.c
@@ -22,13 +22,13 @@ struct {
 } settings;
 
 void init(int argc, char *argv[]) { // return config file
-    settings.config = string_init(CONFIG_FILE);
+    settings.config = strdup(CONFIG_FILE);
     settings.debug = FALSE;
     settings.verbose = FALSE;
 
     if (getenv("CONFIG") != NULL) {
         free(settings.config);
-        settings.config = string_init(getenv("CONFIG"));
+        settings.config = strdup(getenv("CONFIG"));
     }
     if (getenv("DEBUG") != NULL && !strcmp(getenv("DEBUG"), "TRUE")) {
         settings.debug = TRUE;
@@ -55,7 +55,7 @@ void init(int argc, char *argv[]) { // return config file
                 exit(1);
             }
             free(settings.config);
-            settings.config = string_init(argv[++i]); // use custom config file
+            settings.config = strdup(argv[++i]); // use custom config file
         }
     }
     log_debug("Config file -> %s", settings.config);
diff --git a/src/common/json.c b/src/common/json.c
index 18c0aa2..95f33e7 100644
--- a/src/common/json.c
+++ b/src/common/json.c
@@ -1,4 +1,3 @@
-#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include "cJSON.h"
@@ -27,8 +26,7 @@ char* to_json(const char *file) { // convert JSON / TOML / YAML to json format (
     flag[8] = '\0';
 
     char *output_file = string_join("/tmp/to-json-", flag);
-    char *to_json_cmd = (char *)malloc(strlen(file) + strlen(output_file) + 11);
-    sprintf(to_json_cmd, "toJSON %s > %s", file, output_file);
+    char *to_json_cmd = string_load("toJSON %s > %s", file, output_file);
     int to_json_ret = run_command(to_json_cmd);
     free(to_json_cmd);
 
@@ -87,7 +85,7 @@ char* json_string_value(char* caption, cJSON *json) { // json string value -> st
     if (!cJSON_IsString(json)) {
         log_fatal("`%s` must be string", caption);
     }
-    return string_init(json->valuestring);
+    return strdup(json->valuestring);
 }
 
 char** json_string_list_value(char *caption, cJSON *json, char **string_list) { // json string array
diff --git a/src/common/structure.c b/src/common/structure.c
index 4f7f526..2698e86 100644
--- a/src/common/structure.c
+++ b/src/common/structure.c
@@ -2,7 +2,6 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
-#include "sundry.h"
 #include "structure.h"
 
 char** string_list_init() { // init string list
@@ -20,7 +19,7 @@ uint32_t string_list_len(char **string_list) { // get len of string list
 void string_list_append(char ***string_list, const char *string) {
     uint32_t len = string_list_len(*string_list);
     *string_list = (char **)realloc(*string_list, sizeof(char *) * (len + 2)); // extend string list
-    (*string_list)[len] = string_init(string);
+    (*string_list)[len] = strdup(string);
     (*string_list)[len + 1] = NULL; // list end sign
 }
 
@@ -39,7 +38,7 @@ void string_list_free(char **string_list) { // free string list
 
 char* string_list_dump(char **string_list) { // ['a', 'b', 'c', ...]
     if (string_list_len(string_list) == 0) {
-        return string_init("[]"); // empty string list
+        return strdup("[]"); // empty string list
     }
     char *string_ret = (char *)malloc(2);
     strcpy(string_ret, "[");
@@ -86,14 +85,14 @@ void uint32_list_free(uint32_t **uint32_list) { // free uint32 list
 
 char* uint32_list_dump(uint32_t **uint32_list) { // [1, 2, 3, ...]
     if (uint32_list_len(uint32_list) == 0) {
-        return string_init("[]"); // empty int list
+        return strdup("[]"); // empty int list
     }
     char uint32_str[12];
     char *string_ret = (char *)malloc(2);
     strcpy(string_ret, "[");
     for (uint32_t **number = uint32_list; *number != NULL; ++number) {
         sprintf(uint32_str, "%u", **number);
-        string_ret = (char*)realloc(string_ret, strlen(string_ret) + 15);
+        string_ret = (char *)realloc(string_ret, strlen(string_ret) + 15);
         string_ret = strcat(strcat(string_ret, uint32_str), ", ");
     }
     string_ret[strlen(string_ret) - 2] = '\0';
diff --git a/src/common/sundry.c b/src/common/sundry.c
index 1f0edcf..7191199 100644
--- a/src/common/sundry.c
+++ b/src/common/sundry.c
@@ -1,8 +1,13 @@
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE // NOLINT
+#endif
+
 #include <stdio.h>
+#include <stdarg.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sys/time.h>
 #include <unistd.h>
+#include <sys/time.h>
 #include "logger.h"
 #include "constant.h"
 #include "structure.h"
@@ -14,19 +19,23 @@ char* show_bool(uint8_t value) { // return `true` or `false`
     return "false";
 }
 
-char* string_init(const char *str) { // new string
-    return strcpy((char *)malloc(strlen(str) + 1), str);
-}
-
 char* string_join(const char *base, const char *add) { // combine string
     char *ret = (char *)malloc(strlen(base) + strlen(add) + 1);
     return strcat(strcpy(ret, base), add);
 }
 
+char* string_load(const char *fmt, ...) {
+    va_list ap;
+    va_start(ap, fmt);
+    char *buf = NULL;
+    vasprintf(&buf, fmt, ap);
+    return buf;
+}
+
 char* uint32_to_string(uint32_t number) { // convert uint32 -> string
     char to_str[11]; // MAX_LEN(uint32) -> 4294967296(10-bytes)
     sprintf(to_str, "%u", number);
-    return string_init(to_str);
+    return strdup(to_str);
 }
 
 void string_list_debug(char *describe, char **string_list) { // show string list in debug log
diff --git a/src/common/system.c b/src/common/system.c
index 3c32b62..476d579 100644
--- a/src/common/system.c
+++ b/src/common/system.c
@@ -66,8 +66,7 @@ void save_file(const char *file, const char *content) { // save content into fil
 }
 
 void file_append(const char *base_file, const char *append_file) { // append_file >> base_file
-    char *append_cmd = (char *)malloc(strlen(base_file) + strlen(append_file) + 9);
-    sprintf(append_cmd, "cat %s >> %s", append_file, base_file);
+    char *append_cmd = string_load("cat %s >> %s", append_file, base_file);
     run_command(append_cmd);
     free(append_cmd);
 }
@@ -109,8 +108,7 @@ void save_string_list(const char *file, char **string_list) { // save string lis
 
 void download_file(const char *file, const char *url) { // download file
     log_debug("Download file `%s` -> %s", file, url);
-    char *download_cmd = (char *)malloc(strlen(file) + strlen(url) + 15);
-    sprintf(download_cmd, "wget -T 8 -O %s %s", file, url);
+    char *download_cmd = string_load("wget -T 8 -O %s %s", file, url);
     if (run_command(download_cmd)) {
         log_warn("File `%s` download failed", url);
     }
diff --git a/src/loader/config.c b/src/loader/config.c
index 483a585..e5b3117 100644
--- a/src/loader/config.c
+++ b/src/loader/config.c
@@ -1,4 +1,5 @@
 #include <stdlib.h>
+#include <string.h>
 #include "config.h"
 #include "logger.h"
 #include "sundry.h"
@@ -33,11 +34,11 @@ cleardns_config* config_init() { // init config struct of cleardns
 
     config->adguard.port = ADGUARD_PORT;
     config->adguard.enable = TRUE;
-    config->adguard.username = string_init(ADGUARD_USER);
-    config->adguard.password = string_init(ADGUARD_PASSWD);
+    config->adguard.username = strdup(ADGUARD_USER);
+    config->adguard.password = strdup(ADGUARD_PASSWD);
 
     config->assets.disable = FALSE;
-    config->assets.cron = string_init(UPDATE_CRON);
+    config->assets.cron = strdup(UPDATE_CRON);
     config->assets.update_file = string_list_init();
     config->assets.update_url = string_list_init();
 
diff --git a/src/loader/default.c b/src/loader/default.c
index d827ac3..2480f9b 100644
--- a/src/loader/default.c
+++ b/src/loader/default.c
@@ -1,7 +1,7 @@
 #include <stdlib.h>
+#include <string.h>
 #include "json.h"
 #include "logger.h"
-#include "sundry.h"
 #include "system.h"
 
 #define DEFAULT_CONFIG "\
@@ -63,7 +63,7 @@ void load_default_config(const char *config_file) {
         remove_file(temp_file);
     }
     if (config_content == NULL) {
-        config_content = string_init(DEFAULT_CONFIG);
+        config_content = strdup(DEFAULT_CONFIG);
     }
     save_file(config_file, config_content);
     free(config_content);
diff --git a/src/loader/loader.c b/src/loader/loader.c
index 5e375ea..6914654 100644
--- a/src/loader/loader.c
+++ b/src/loader/loader.c
@@ -1,5 +1,5 @@
-#include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include "config.h"
 #include "loader.h"
 #include "logger.h"
@@ -63,14 +63,14 @@ overture* load_diverter(cleardns_config *config) {
 
     if (string_list_len(config->ttl)) {
         free(diverter->ttl_file);
-        diverter->ttl_file = string_init(ASSET_TTL);
+        diverter->ttl_file = strdup(ASSET_TTL);
         char *ttl_file = string_join(WORK_DIR, ASSET_TTL);
         save_string_list(ttl_file, config->ttl);
         free(ttl_file);
     }
     if (string_list_len(config->hosts)) {
         free(diverter->host_file);
-        diverter->host_file = string_init(ASSET_HOSTS);
+        diverter->host_file = strdup(ASSET_HOSTS);
         char *hosts_file = string_join(WORK_DIR, ASSET_HOSTS);
         save_string_list(hosts_file, config->hosts);
         free(hosts_file);
@@ -79,9 +79,9 @@ overture* load_diverter(cleardns_config *config) {
     free(diverter->domestic_ip_file);
     free(diverter->foreign_domain_file);
     free(diverter->domestic_domain_file);
-    diverter->domestic_ip_file = string_init(ASSET_CHINA_IP);
-    diverter->foreign_domain_file = string_init(ASSET_GFW_LIST);
-    diverter->domestic_domain_file = string_init(ASSET_CHINA_LIST);
+    diverter->domestic_ip_file = strdup(ASSET_CHINA_IP);
+    diverter->foreign_domain_file = strdup(ASSET_GFW_LIST);
+    diverter->domestic_domain_file = strdup(ASSET_CHINA_LIST);
 
     char *gfwlist = string_join(WORK_DIR, ASSET_GFW_LIST);
     char *china_ip = string_join(WORK_DIR, ASSET_CHINA_IP);
@@ -108,8 +108,8 @@ adguard* load_filter(cleardns_config *config) {
     adguard *filter = adguard_init();
     filter->dns_port = config->port;
     filter->web_port = config->adguard.port;
-    filter->username = string_init(config->adguard.username);
-    filter->password = string_init(config->adguard.password);
+    filter->username = strdup(config->adguard.username);
+    filter->password = strdup(config->adguard.password);
     char *diverter_port = uint32_to_string(config->diverter.port);
     filter->upstream = string_join("127.0.0.1:", diverter_port);
     free(diverter_port);
@@ -121,7 +121,7 @@ crontab* load_crond(cleardns_config *config) {
         return NULL; // disable crond
     }
     crontab *crond = crontab_init();
-    crond->cron = string_init(config->assets.cron);
+    crond->cron = strdup(config->assets.cron);
     return crond;
 }
 
diff --git a/src/utils/assets.c b/src/utils/assets.c
index 6b9bb89..9f31f42 100644
--- a/src/utils/assets.c
+++ b/src/utils/assets.c
@@ -1,4 +1,3 @@
-#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <signal.h>
@@ -81,8 +80,7 @@ void extract(const char *file) { // extract one asset file from `.tar.xz` file
     }
     free(output_file);
 
-    char *extract_cmd = (char *)malloc(strlen(ASSETS_PKG) + strlen(file) + strlen(ASSETS_DIR) + 13);
-    sprintf(extract_cmd, "tar xf %s %s -C %s", ASSETS_PKG, file, ASSETS_DIR);
+    char *extract_cmd = string_load("tar xf %s %s -C %s", ASSETS_PKG, file, ASSETS_DIR);
     if (run_command(extract_cmd)) {
         log_warn("Extract asset `%s` failed", file);
     } else {
diff --git a/src/utils/process.c b/src/utils/process.c
index ccb1834..f4c2ed4 100644
--- a/src/utils/process.c
+++ b/src/utils/process.c
@@ -3,6 +3,7 @@
 #endif
 
 #include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
 #include <sys/wait.h>
 #include <sys/prctl.h>
@@ -28,7 +29,7 @@ void process_exec(process *proc);
 process* process_init(const char *caption, const char *bin) { // init process struct
     process *proc = (process *)malloc(sizeof(process));
     proc->pid = 0; // process not running
-    proc->name = string_init(caption); // process caption
+    proc->name = strdup(caption); // process caption
     proc->cmd = string_list_init();
     string_list_append(&proc->cmd, bin); // argv[0] normally be process file name
     proc->env = string_list_init(); // empty environment variable
@@ -116,7 +117,7 @@ char* get_exit_msg(int status) { // get why the child process death
         free(exit_sig);
         return exit_msg;
     }
-    return string_init("Unknown reason");
+    return strdup("Unknown reason");
 }
 
 void server_exit(int exit_code) { // kill sub process and exit