shlwapi: Fix StrCpyNW to deal with null inputs better, and don't use lstrcpynW.

dlls/shlwapi/string.c

@@ -507,22 +507,32 @@ LPWSTR WINAPI StrCpyW(LPWSTR lpszStr, LPCWSTR lpszSrc)
  * Copy a string to another string, up to a maximum number of characters.
  *
  * PARAMS
- *  lpszStr  [O] Destination string
- *  lpszSrc  [I] Source string
- *  iLen     [I] Maximum number of chars to copy
+ *  dst    [O] Destination string
+ *  src    [I] Source string
+ *  count  [I] Maximum number of chars to copy
  *
  * RETURNS
- *  lpszStr.
+ *  dst.
  */
-LPWSTR WINAPI StrCpyNW(LPWSTR lpszStr, LPCWSTR lpszSrc, int iLen)
+LPWSTR WINAPI StrCpyNW(LPWSTR dst, LPCWSTR src, int count)
 {
-  TRACE("(%p,%s,%i)\n", lpszStr, debugstr_w(lpszSrc), iLen);
+  LPWSTR d = dst;
+  LPCWSTR s = src;
 
-  lstrcpynW(lpszStr, lpszSrc, iLen);
-  return lpszStr;
-}
+  TRACE("(%p,%s,%i)\n", dst, debugstr_w(src), count);
 
+  if (s)
+  {
+    while ((count > 1) && *s)
+    {
+      count--;
+      *d++ = *s++;
+    }
+  }
+  if (count) *d = 0;
 
+  return dst;
+}
 
 /*************************************************************************
  * SHLWAPI_StrStrHelperA

dlls/shlwapi/tests/string.c

@@ -863,6 +863,33 @@ static void test_StrXXX_overflows(void)
     else
         win_skip("StrCatBuffA() is not available\n");
 
+if (0)
+{
+    /* crashes on XP */
+    StrCpyNW(wbuf, (LPCWSTR)0x1, 10);
+    StrCpyNW((LPWSTR)0x1, wstr1, 10);
+}
+
+    memset(wbuf, 0xbf, sizeof(wbuf));
+    expect_eq(StrCpyNW(wbuf, (LPCWSTR)0x1, 1), wbuf, PWCHAR, "%p");
+    expect_eq(wbuf[0], 0, WCHAR, "%x");
+    expect_eq(wbuf[1], (WCHAR)0xbfbf, WCHAR, "%x");
+
+    memset(wbuf, 0xbf, sizeof(wbuf));
+    expect_eq(StrCpyNW(wbuf, 0, 10), wbuf, PWCHAR, "%p");
+    expect_eq(wbuf[0], 0, WCHAR, "%x");
+    expect_eq(wbuf[1], (WCHAR)0xbfbf, WCHAR, "%x");
+
+    memset(wbuf, 0xbf, sizeof(wbuf));
+    expect_eq(StrCpyNW(wbuf, 0, 0), wbuf, PWCHAR, "%p");
+    expect_eq(wbuf[0], (WCHAR)0xbfbf, WCHAR, "%x");
+    expect_eq(wbuf[1], (WCHAR)0xbfbf, WCHAR, "%x");
+
+    memset(wbuf, 0xbf, sizeof(wbuf));
+    expect_eq(StrCpyNW(wbuf, wstr1, 0), wbuf, PWCHAR, "%p");
+    expect_eq(wbuf[0], (WCHAR)0xbfbf, WCHAR, "%x");
+    expect_eq(wbuf[1], (WCHAR)0xbfbf, WCHAR, "%x");
+
     memset(wbuf, 0xbf, sizeof(wbuf));
     expect_eq(StrCpyNW(wbuf, wstr1, 10), wbuf, PWCHAR, "%p");
     expect_eq(wbuf[9], 0, WCHAR, "%x");