libc: Add strncpy and strncat, and deprecate strcpy and strcat (which, since we're building with -Werror, is an instant ban from using these functions)

libs/libc/include/string.h

@@ -1,6 +1,7 @@
 #ifndef _STRING_H
 #define _STRING_H
 
+#include <_/macros.h>
 #include <stddef.h>
 
 #ifdef __cplusplus
@@ -10,12 +11,18 @@ extern "C"
 
     void* memcpy(void*, const void*, size_t);
     void* memset(void*, int, size_t);
-    size_t strlen(const char*);
-    char* strcpy(char*, const char*);
-    char* strchr(const char*, int);
-    char* strcat(char*, const char*);
     void* memclr(void*, size_t);
 
+    size_t strlen(const char*);
+
+    deprecated("strcpy is unsafe and should not be used; use strncpy instead") char* strcpy(char*, const char*);
+    char* strncpy(char*, const char*, size_t);
+
+    char* strchr(const char*, int);
+
+    deprecated("strcat is unsafe and should not be used; use strncat instead") char* strcat(char*, const char*);
+    char* strncat(char*, const char*, size_t);
+
 #ifdef __cplusplus
 }
 #endif

libs/libc/src/printf.cpp

@@ -290,7 +290,7 @@ extern "C"
         return internal_printf(
             format,
             [&](const char* s) {
-                if (str) strcat(str, s);
+                if (str) strncat(str, s, 1025);
             },
             -1, ap);
     }
@@ -300,7 +300,7 @@ extern "C"
         return internal_printf(
             format,
             [&](const char* s) {
-                if (str) strcat(str, s);
+                if (str) strncat(str, s, 1025);
             },
             max == 0 ? 0 : max - 1, ap);
     }

libs/libc/src/string.cpp

@@ -29,6 +29,13 @@ extern "C"
         return dest;
     }
 
+    char* strncpy(char* dest, const char* src, size_t n)
+    {
+        size_t src_len = strlen(src) + 1; // NULL byte
+        memcpy(dest, src, src_len > n ? n : src_len);
+        return dest;
+    }
+
     char* strcat(char* dest, const char* src)
     {
         size_t dest_len = strlen(dest);
@@ -41,6 +48,18 @@ extern "C"
         return dest;
     }
 
+    char* strncat(char* dest, const char* src, size_t n)
+    {
+        size_t dest_len = strlen(dest);
+        size_t i;
+
+        for (i = 0; i < n && *(src + i); i++) *(char*)(dest + dest_len + i) = *(char*)(src + i);
+
+        *(char*)(dest + dest_len + i) = '\0';
+
+        return dest;
+    }
+
     char* strchr(const char*, int)
     {
         NOT_IMPLEMENTED("strchr");