winpr: fix PathCchAddBackslash

The HRESULT S_FALSE does not indicate an error:
- return E_INVALIDARG instead of S_FALSE
- return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER) instead of S_FALSE

Also extended/fixed the corresponding ctest

winpr/libwinpr/path/include/PathCchAddSeparator.c

@@ -12,7 +12,7 @@ HRESULT PATH_CCH_ADD_SEPARATOR(PWSTR pszPath, size_t cchPath)
 	size_t pszPathLength;
 
 	if (!pszPath)
-		return S_FALSE;
+		return E_INVALIDARG;
 
 	pszPathLength = lstrlenW(pszPath);
 
@@ -27,7 +27,7 @@ HRESULT PATH_CCH_ADD_SEPARATOR(PWSTR pszPath, size_t cchPath)
 		return S_OK;
 	}
 
-	return S_FALSE;
+	return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER);
 }
 
 #else
@@ -37,7 +37,7 @@ HRESULT PATH_CCH_ADD_SEPARATOR(PSTR pszPath, size_t cchPath)
 	size_t pszPathLength;
 
 	if (!pszPath)
-		return S_FALSE;
+		return E_INVALIDARG;
 
 	pszPathLength = lstrlenA(pszPath);
 
@@ -52,7 +52,7 @@ HRESULT PATH_CCH_ADD_SEPARATOR(PSTR pszPath, size_t cchPath)
 		return S_OK;
 	}
 
-	return S_FALSE;
+	return HRESULT_FROM_WIN32(ERROR_INSUFFICIENT_BUFFER);
 }
 
 #endif

winpr/libwinpr/path/test/TestPathCchAddBackslash.c

@@ -13,6 +13,12 @@ int TestPathCchAddBackslash(int argc, char* argv[])
 	HRESULT status;
 	TCHAR Path[PATHCCH_MAX_CCH];
 
+	/**
+	 * PathCchAddBackslash returns S_OK if the function was successful,
+	 * S_FALSE if the path string already ends in a backslash,
+	 * or an error code otherwise.
+	 */
+
 	_tcscpy(Path, testPathNoBackslash);
 
 	/* Add a backslash to a path without a trailing backslash, expect S_OK */
@@ -21,7 +27,7 @@ int TestPathCchAddBackslash(int argc, char* argv[])
 
 	if (status != S_OK)
 	{
-		_tprintf(_T("PathCchAddBackslash status: 0x%08X\n"), (int) status);
+		_tprintf(_T("PathCchAddBackslash status: 0x%08X\n"), (unsigned) status);
 		return -1;
 	}
 
@@ -39,7 +45,7 @@ int TestPathCchAddBackslash(int argc, char* argv[])
 
 	if (status != S_FALSE)
 	{
-		_tprintf(_T("PathCchAddBackslash status: 0x%08X\n"), (int) status);
+		_tprintf(_T("PathCchAddBackslash status: 0x%08X\n"), (unsigned) status);
 		return -1;
 	}
 
@@ -49,6 +55,40 @@ int TestPathCchAddBackslash(int argc, char* argv[])
 		return -1;
 	}
 
+	/* Use NULL PSTR, expect FAILED(status) */
+
+	status = PathCchAddBackslash(NULL, PATHCCH_MAX_CCH);
+
+	if (SUCCEEDED(status))
+	{
+		_tprintf(_T("PathCchAddBackslash unexpectedly succeded with null buffer. Status: 0x%08X\n"), (unsigned) status);
+		return -1;
+	}
+
+	/* Use insufficient size value, expect FAILED(status)  */
+
+	_tcscpy(Path, _T("C:\\tmp"));
+
+	status = PathCchAddBackslash(Path, 7);
+
+	if (SUCCEEDED(status))
+	{
+		_tprintf(_T("PathCchAddBackslash unexpectedly succeded with insufficient buffer size. Status: 0x%08X\n"), (unsigned) status);
+		return -1;
+	}
+
+	/* Use minimum required size value, expect S_OK  */
+
+	_tcscpy(Path, _T("C:\\tmp"));
+
+	status = PathCchAddBackslash(Path, 8);
+
+	if (status != S_OK)
+	{
+		_tprintf(_T("PathCchAddBackslash failed with status: 0x%08X\n"), (unsigned) status);
+		return -1;
+	}
+
 	return 0;
 }