patch 9.1.0518: initialize the random buffer can be improved

Problem:  initialize the random buffer can be improved
Solution: refactor init_srand() function, move machine-specific parts to
          os_mswin and os_unix, implement a fallback for Windows 10 and
          later (LemonBoy)

closes: #15125

Signed-off-by: LemonBoy <thatlemon@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/evalfunc.c

@@ -9267,47 +9267,26 @@ f_test_srand_seed(typval_T *argvars, typval_T *rettv UNUSED)
     static void
 init_srand(UINT32_T *x)
 {
-#ifndef MSWIN
+    struct {
-    static int dev_urandom_state = NOTDONE;  // FAIL or OK once tried
+	union {
-#endif
+	    UINT32_T number;
+	    char_u   bytes[sizeof(UINT32_T)];
+	} contents;
+    } buf;
 
     if (srand_seed_for_testing_is_used)
     {
 	*x = srand_seed_for_testing;
 	return;
     }
-#ifndef MSWIN
-    if (dev_urandom_state != FAIL)
-    {
-	int  fd = open("/dev/urandom", O_RDONLY);
-	struct {
-	    union {
-		UINT32_T number;
-		char     bytes[sizeof(UINT32_T)];
-	    } contents;
-	} buf;
 
-	// Attempt reading /dev/urandom.
+    if (mch_get_random(buf.contents.bytes, sizeof(buf.contents.bytes)) == OK)
-	if (fd == -1)
-	    dev_urandom_state = FAIL;
-	else
     {
-	    buf.contents.number = 0;
-	    if (read(fd, buf.contents.bytes, sizeof(UINT32_T))
-							   != sizeof(UINT32_T))
-		dev_urandom_state = FAIL;
-	    else
-	    {
-		dev_urandom_state = OK;
 	*x = buf.contents.number;
+	return;
     }
-	    close(fd);
+
-	}
+    // The system's random number generator doesn't work, fall back to:
-    }
-    if (dev_urandom_state != OK)
-#endif
-    {
-	// Reading /dev/urandom doesn't work, fall back to:
     // - randombytes_random()
     // - reltime() or time()
     // - XOR with process ID
@@ -9330,7 +9309,6 @@ init_srand(UINT32_T *x)
 #endif
 	*x ^= mch_get_pid();
     }
-    }
 }
 
 #define ROTL(x, k) (((x) << (k)) | ((x) >> (32 - (k))))

src/os_mswin.c

@@ -830,6 +830,40 @@ mch_icon_load(HANDLE *iconp)
 						  0, mch_icon_load_cb, iconp);
 }
 
+/*
+ * Fill the buffer 'buf' with 'len' random bytes.
+ * Returns FAIL if the OS PRNG is not available or something went wrong.
+ */
+    int
+mch_get_random(char_u *buf, int len)
+{
+    static int		initialized = NOTDONE;
+    static HINSTANCE	hInstLib;
+    static BOOL (WINAPI *pProcessPrng)(PUCHAR, ULONG);
+
+    if (initialized == NOTDONE)
+    {
+	hInstLib = vimLoadLib("bcryptprimitives.dll");
+	if (hInstLib != NULL)
+	    pProcessPrng = (void *)GetProcAddress(hInstLib, "ProcessPrng");
+	if (hInstLib == NULL || pProcessPrng == NULL)
+	{
+	    FreeLibrary(hInstLib);
+	    initialized = FAIL;
+	}
+	else
+	    initialized = OK;
+    }
+
+    if (initialized == FAIL)
+	return FAIL;
+
+    // According to the documentation this call cannot fail.
+    pProcessPrng(buf, len);
+
+    return OK;
+}
+
     int
 mch_libcall(
     char_u	*libname,

src/os_unix.c

@@ -7722,6 +7722,34 @@ sig_sysmouse SIGDEFARG(sigarg)
 }
 #endif // FEAT_SYSMOUSE
 
+/*
+ * Fill the buffer 'buf' with 'len' random bytes.
+ * Returns FAIL if the OS PRNG is not available or something went wrong.
+ */
+    int
+mch_get_random(char_u *buf, int len)
+{
+    static int dev_urandom_state = NOTDONE;
+
+    if (dev_urandom_state == FAIL)
+	return FAIL;
+
+    int fd = open("/dev/urandom", O_RDONLY);
+
+    // Attempt reading /dev/urandom.
+    if (fd == -1)
+	dev_urandom_state = FAIL;
+    else if (read(fd, buf, len) == len)
+	dev_urandom_state = OK;
+    else
+    {
+	dev_urandom_state = FAIL;
+	close(fd);
+    }
+
+    return dev_urandom_state;
+}
+
 #if defined(FEAT_LIBCALL) || defined(PROTO)
 typedef char_u * (*STRPROCSTR)(char_u *);
 typedef char_u * (*INTPROCSTR)(int);

src/proto/os_mswin.pro

@@ -23,6 +23,7 @@ int mch_has_wildcard(char_u *p);
 int mch_chdir(char *path);
 int mch_icon_load(HANDLE *iconp);
 int mch_libcall(char_u *libname, char_u *funcname, char_u *argstring, int argint, char_u **string_result, int *number_result);
+int mch_get_random(char_u *buf, int len);
 void DumpPutS(const char *psz);
 int mch_get_winpos(int *x, int *y);
 void mch_set_winpos(int x, int y);

src/proto/os_unix.pro

@@ -76,6 +76,7 @@ int mch_rename(const char *src, const char *dest);
 int gpm_available(void);
 int gpm_enabled(void);
 int mch_libcall(char_u *libname, char_u *funcname, char_u *argstring, int argint, char_u **string_result, int *number_result);
+int mch_get_random(char_u *buf, int len);
 void setup_term_clip(void);
 void start_xterm_trace(int button);
 void stop_xterm_trace(void);

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    518,
 /**/
     517,
 /**/