libc: Add mkdtemp() and mkstemp()

No mktemp() though, as it has race conditions and was removed in POSIX.1-2008.

libc/include/stdlib.h

@@ -131,6 +131,12 @@ extern "C"
     /* Convert a wide character string to a multibyte character string. */
     size_t wcstombs(char* buf, const wchar_t* src, size_t max);
 
+    /* Create a unique directory from a template string whose last 6 bytes must be XXXXXX. */
+    char* mkdtemp(char* _template);
+
+    /* Create a unique file from a template string whose last 6 bytes must be XXXXXX. */
+    int mkstemp(char* _template);
+
 #ifdef __cplusplus
 }
 #endif

libc/src/stdlib.cpp

@@ -1,10 +1,13 @@
 #include <errno.h>
+#include <fcntl.h>
 #include <limits.h>
 #include <luna/Heap.h>
 #include <luna/NumberParsing.h>
 #include <luna/Sort.h>
 #include <luna/Utf8.h>
 #include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
 #include <sys/syscall.h>
 #include <sys/wait.h>
 #include <unistd.h>
@@ -218,4 +221,66 @@ extern "C"
     {
         next = seed;
     }
+
+    static void generate_random_character(char* ptr)
+    {
+        constexpr const char chars[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_";
+        *ptr = chars[rand() % sizeof(chars)];
+    }
+
+    static int check_template(char* _template, size_t* len)
+    {
+        *len = strlen(_template);
+        if (*len < 6)
+        {
+            errno = EINVAL;
+            return -1;
+        }
+
+        if (strncmp(_template + (*len - 6), "XXXXXX", 6))
+        {
+            errno = EINVAL;
+            return -1;
+        }
+
+        return 0;
+    }
+
+    static void generate_random_name(char* _template, const size_t* len)
+    {
+        size_t index = *len - 6;
+        while (index < *len) generate_random_character(&_template[index++]);
+    }
+
+    char* mkdtemp(char* _template)
+    {
+        size_t len;
+        if (check_template(_template, &len) < 0) return nullptr;
+
+        while (true)
+        {
+            generate_random_name(_template, &len);
+
+            if (mkdir(_template, 0700) == 0) return _template;
+
+            if (errno != EEXIST) return nullptr;
+        }
+    }
+
+    int mkstemp(char* _template)
+    {
+        size_t len;
+        if (check_template(_template, &len) < 0) return -1;
+
+        while (true)
+        {
+            generate_random_name(_template, &len);
+
+            int fd;
+
+            if ((fd = open(_template, O_RDWR | O_CREAT | O_EXCL, 0600)) >= 0) return fd;
+
+            if (errno != EEXIST) return -1;
+        }
+    }
 }