wininet: Properly handle output buffer size in InternetGetCookieA.

dlls/wininet/cookie.c

@@ -678,7 +678,7 @@ BOOL WINAPI InternetGetCookieA(LPCSTR lpszUrl, LPCSTR lpszCookieName,
     LPSTR lpCookieData, LPDWORD lpdwSize)
 {
     WCHAR *url, *name;
-    DWORD len;
+    DWORD len, size;
     BOOL r;
 
     TRACE("(%s %s %p %p(%u))\n", debugstr_a(lpszUrl), debugstr_a(lpszCookieName),
@@ -701,8 +701,18 @@ BOOL WINAPI InternetGetCookieA(LPCSTR lpszUrl, LPCSTR lpszCookieName,
         {
             r = InternetGetCookieW( url, name, szCookieData, &len );
 
-            *lpdwSize = WideCharToMultiByte( CP_ACP, 0, szCookieData, len,
-                                             lpCookieData, lpCookieData ? *lpdwSize : 0, NULL, NULL );
+            if(r) {
+                size = WideCharToMultiByte( CP_ACP, 0, szCookieData, len, NULL, 0, NULL, NULL);
+                if(lpCookieData) {
+                    if(*lpdwSize >= size) {
+                        WideCharToMultiByte( CP_ACP, 0, szCookieData, len, lpCookieData, *lpdwSize, NULL, NULL);
+                    }else {
+                        SetLastError(ERROR_INSUFFICIENT_BUFFER);
+                        r = FALSE;
+                    }
+                }
+                *lpdwSize = size;
+            }
 
             heap_free( szCookieData );
         }

dlls/wininet/tests/internet.c

@@ -414,6 +414,13 @@ static void test_complicated_cookie(void)
   ok(strstr(buffer,"M=N")==NULL,"M=N present\n");
   ok(strstr(buffer,"O=P")==NULL,"O=P present\n");
 
+  len = 10;
+  memset(buffer, 0xac, sizeof(buffer));
+  ret = InternetGetCookie("http://testing.example.com", NULL, buffer, &len);
+  ok(!ret && GetLastError() == ERROR_INSUFFICIENT_BUFFER,
+     "InternetGetCookie returned: %x(%u), expected ERROR_INSUFFICIENT_BUFFER\n", ret, GetLastError());
+  ok(len == 19, "len = %u\n", len);
+
   len = 1024;
   ret = InternetGetCookieW(testing_example_comW, NULL, NULL, &len);
   ok(ret == TRUE,"InternetGetCookieW failed\n");