windows: Use BCryptGenRandom to implement os.urandom.

Fix urandom not working on windows (there's no /dev/urandom) by using
a proper cryptographic random function (same one as CPython >= 3.11).

ports/unix/moduos.c

@@ -39,6 +39,11 @@
 #endif
 #endif
 
+#if _WIN32
+#include <windows.h>
+#include <bcrypt.h>
+#endif
+
 STATIC mp_obj_t mp_uos_getenv(mp_obj_t var_in) {
     const char *s = getenv(mp_obj_str_get_str(var_in));
     if (s == NULL) {
@@ -100,6 +105,12 @@ STATIC mp_obj_t mp_uos_urandom(mp_obj_t num) {
     mp_int_t n = mp_obj_get_int(num);
     vstr_t vstr;
     vstr_init_len(&vstr, n);
+    #if _WIN32
+    NTSTATUS result = BCryptGenRandom(NULL, (unsigned char *)vstr.buf, n, BCRYPT_USE_SYSTEM_PREFERRED_RNG);
+    if (!BCRYPT_SUCCESS(result)) {
+        mp_raise_OSError(errno);
+    }
+    #else
     #ifdef _HAVE_GETRANDOM
     RAISE_ERRNO(getrandom(vstr.buf, n, 0), errno);
     #else
@@ -108,6 +119,7 @@ STATIC mp_obj_t mp_uos_urandom(mp_obj_t num) {
     RAISE_ERRNO(read(fd, vstr.buf, n), errno);
     close(fd);
     #endif
+    #endif
     return mp_obj_new_str_from_vstr(&mp_type_bytes, &vstr);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(mp_uos_urandom_obj, mp_uos_urandom);

ports/windows/Makefile

@@ -33,7 +33,7 @@ INC += -I$(VARIANT_DIR)
 
 # compiler settings
 CFLAGS = $(INC) -Wall -Wpointer-arith -Wdouble-promotion -Werror -std=gnu99 -DUNIX -D__USE_MINGW_ANSI_STDIO=1 $(CFLAGS_MOD) $(COPT) $(CFLAGS_EXTRA)
-LDFLAGS = $(LDFLAGS_MOD) -lm $(LDFLAGS_EXTRA)
+LDFLAGS = $(LDFLAGS_MOD) -lm -lbcrypt $(LDFLAGS_EXTRA)
 
 # Debugging/Optimization
 ifdef DEBUG

ports/windows/msvc/common.props

@@ -32,6 +32,7 @@
     <Link>
       <GenerateDebugInformation>true</GenerateDebugInformation>
       <GenerateMapFile>true</GenerateMapFile>
+      <AdditionalDependencies>Bcrypt.lib;%(AdditionalDependencies)</AdditionalDependencies>
     </Link>
   </ItemDefinitionGroup>
   <ItemGroup>