diff --git a/src/bind.c b/src/bind.c
index e0cf1a3..2da5646 100644
--- a/src/bind.c
+++ b/src/bind.c
@@ -165,7 +165,7 @@ gt_bind(int argc, char **argv)
     }
 
     char tun_name[64];
-    const int tun_fd = tun_create(tun_name, sizeof(tun_name) - 1, dev);
+    const int tun_fd = tun_create(tun_name, sizeof(tun_name), dev);
 
     if (tun_fd == -1) {
         gt_log("couldn't create tun device\n");
diff --git a/src/ctl.c b/src/ctl.c
index f28529f..cbc708f 100644
--- a/src/ctl.c
+++ b/src/ctl.c
@@ -2,6 +2,7 @@
 #include "ctl.h"
 #include "str.h"
 
+#include <stdio.h>
 #include <unistd.h>
 #include <dirent.h>
 #include <sys/socket.h>
@@ -41,17 +42,15 @@ ctl_setsun(struct sockaddr_un *dst, const char *dir, const char *file)
         .sun_family = AF_UNIX,
     };
 
-    const char *path[] = {dir, "/", file};
-    const size_t len = sizeof(sun.sun_path) - 1;
+    int ret = snprintf(sun.sun_path, sizeof(sun.sun_path), "%s/%s", dir, file);
 
-    if (str_cat(sun.sun_path, len, path, COUNT(path)) == len) {
-        if (str_cat(NULL, len + 1, path, COUNT(path)) > len) {
-            errno = EINVAL;
-            return -1;
-        }
+    if (ret <= 0 || (size_t)ret >= sizeof(sun.sun_path)) {
+        errno = EINVAL;
+        return -1;
     }
 
-    *dst = sun;
+    if (dst)
+        *dst = sun;
 
     return 0;
 }
diff --git a/src/iface.c b/src/iface.c
index 1728155..c39af08 100644
--- a/src/iface.c
+++ b/src/iface.c
@@ -1,7 +1,7 @@
 #include "common.h"
 #include "iface.h"
-#include "str.h"
 
+#include <stdio.h>
 #include <net/if.h>
 #include <sys/ioctl.h>
 
@@ -17,13 +17,11 @@ iface_set_mtu(const char *dev_name, size_t mtu)
         .ifr_mtu = (int)mtu,
     };
 
-    const size_t len = sizeof(ifr.ifr_name) - 1;
+    int ret = snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "%s", dev_name);
 
-    if (str_cpy(ifr.ifr_name, len, dev_name) == len) {
-        if (str_len(dev_name, len + 1) > len) {
-            errno = EINTR;
-            return -1;
-        }
+    if (ret <= 0 || (size_t)ret >= sizeof(ifr.ifr_name)) {
+        errno = EINTR;
+        return -1;
     }
 
     int fd = socket(AF_INET, SOCK_DGRAM, 0);
@@ -31,7 +29,7 @@ iface_set_mtu(const char *dev_name, size_t mtu)
     if (fd == -1)
         return -1;
 
-    int ret = ioctl(fd, SIOCSIFMTU, &ifr);
+    ret = ioctl(fd, SIOCSIFMTU, &ifr);
 
     int err = errno;
     close(fd);
diff --git a/src/str.h b/src/str.h
index b547c6a..b012277 100644
--- a/src/str.h
+++ b/src/str.h
@@ -31,32 +31,3 @@ str_len(const char *restrict str, size_t len)
 
     return strnlen(str, len);
 }
-
-static inline size_t
-str_cat(char *dst, size_t dst_len, const char **src, size_t count)
-{
-    if (count && !src)
-        return 0;
-
-    size_t len = 0;
-
-    for (size_t i = 0; i < count && dst_len > len; i++) {
-        size_t n = str_len(src[i], dst_len - len);
-
-        if (dst && n)
-            memmove(&dst[len], src[i], n);
-
-        len += n;
-    }
-
-    if (dst)
-        dst[len] = 0;
-
-    return len;
-}
-
-static inline size_t
-str_cpy(char *dst, size_t dst_len, const char *src)
-{
-    return str_cat(dst, dst_len, &src, 1);
-}
diff --git a/src/tun.c b/src/tun.c
index d519542..05c0a1e 100644
--- a/src/tun.c
+++ b/src/tun.c
@@ -32,9 +32,9 @@
 static int
 tun_create_by_id(char *name, size_t len, unsigned id)
 {
-    int ret = snprintf(name, len + 1, "utun%u", id);
+    int ret = snprintf(name, len, "utun%u", id);
 
-    if (ret <= 0 || ret > len) {
+    if (ret <= 0 || (size_t)ret >= len) {
         errno = EINVAL;
         return -1;
     }
@@ -44,8 +44,9 @@ tun_create_by_id(char *name, size_t len, unsigned id)
     if (fd == -1)
         return -1;
 
-    struct ctl_info ci = {0};
-    str_cpy(ci.ctl_name, sizeof(ci.ctl_name) - 1, UTUN_CONTROL_NAME);
+    struct ctl_info ci = {
+        .ctl_name = UTUN_CONTROL_NAME,
+    };
 
     if (ioctl(fd, CTLIOCGINFO, &ci)) {
         int err = errno;
@@ -96,10 +97,9 @@ tun_create_by_name(char *name, size_t len, const char *dev_name)
         .ifr_flags = IFF_TUN | IFF_NO_PI,
     };
 
-    const size_t ifr_len = sizeof(ifr.ifr_name) - 1;
+    int ret = snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), "%s", dev_name);
 
-    if ((len < ifr_len) ||
-        (str_len(dev_name, ifr_len + 1) > ifr_len)) {
+    if (ret <= 0 || (size_t)ret >= sizeof(ifr.ifr_name)) {
         errno = EINVAL;
         return -1;
     }
@@ -109,8 +109,6 @@ tun_create_by_name(char *name, size_t len, const char *dev_name)
     if (fd == -1)
         return -1;
 
-    str_cpy(ifr.ifr_name, ifr_len, dev_name);
-
     if (ioctl(fd, TUNSETIFF, &ifr)) {
         int err = errno;
         close(fd);
@@ -118,8 +116,6 @@ tun_create_by_name(char *name, size_t len, const char *dev_name)
         return -1;
     }
 
-    str_cpy(name, len, ifr.ifr_name);
-
     return fd;
 }
 
@@ -128,21 +124,13 @@ tun_create_by_name(char *name, size_t len, const char *dev_name)
 static int
 tun_create_by_name(char *name, size_t len, const char *dev_name)
 {
-    char tmp[128];
-    int ret = snprintf(tmp, sizeof(tmp), "/dev/%s", dev_name);
+    int ret = snprintf(name, len, "/dev/%s", dev_name);
 
-    if (ret <= 0 || (size_t)ret >= sizeof(tmp)) {
+    if (ret <= 0 || (size_t)ret >= len) {
         errno = EINVAL;
         return -1;
     }
 
-    if (str_cpy(name, len, dev_name) == len) {
-        if (str_len(dev_name, len + 1) > len) {
-            errno = EINVAL;
-            return -1;
-        }
-    }
-
     return open(tmp, O_RDWR);
 }