unix/modos: Add support for uos.urandom(n).

Use getrandom function if available, otherwise read from /dev/urandom.

Signed-off-by: Henk.Vergonet@gmail.com

ports/unix/modos.c

@@ -27,6 +27,7 @@
 
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <fcntl.h>
 #include <unistd.h>
 #include <errno.h>
 #include <stdio.h>
@@ -49,6 +50,29 @@
 #define USE_STATFS 1
 #endif
 
+#if defined(__GLIBC__) && defined(__GLIBC_PREREQ)
+#if __GLIBC_PREREQ(2, 25)
+#include <sys/random.h>
+#define _HAVE_GETRANDOM
+#endif
+#endif
+
+STATIC mp_obj_t mod_os_urandom(mp_obj_t num) {
+    mp_int_t n = mp_obj_get_int(num);
+    vstr_t vstr;
+    vstr_init_len(&vstr, n);
+    #ifdef _HAVE_GETRANDOM
+    RAISE_ERRNO(getrandom(vstr.buf, n, 0), errno);
+    #else
+    int fd = open("/dev/urandom", O_RDONLY);
+    RAISE_ERRNO(fd, errno);
+    RAISE_ERRNO(read(fd, vstr.buf, n), errno);
+    close(fd);
+    #endif
+    return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(mod_os_urandom_obj, mod_os_urandom);
+
 STATIC mp_obj_t mod_os_stat(mp_obj_t path_in) {
     struct stat sb;
     const char *path = mp_obj_str_get_str(path_in);
@@ -309,6 +333,7 @@ STATIC const mp_rom_map_elem_t mp_module_os_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_uos) },
     { MP_ROM_QSTR(MP_QSTR_errno), MP_ROM_PTR(&mod_os_errno_obj) },
     { MP_ROM_QSTR(MP_QSTR_stat), MP_ROM_PTR(&mod_os_stat_obj) },
+    { MP_ROM_QSTR(MP_QSTR_urandom), MP_ROM_PTR(&mod_os_urandom_obj) },
     #if MICROPY_PY_OS_STATVFS
     { MP_ROM_QSTR(MP_QSTR_statvfs), MP_ROM_PTR(&mod_os_statvfs_obj) },
     #endif