Verify custom save path is an absolute path.

PiperOrigin-RevId: 952971544

internal/base/files.cc

@@ -142,4 +142,8 @@ std::optional<size_t> Files::GetAvailableDiskSpaceInBytes(
   return std::nullopt;
 }
 
+bool Files::IsAbsolutePath(const FilePath& path) {
+  return path.path_.is_absolute();
+}
+
 }  // namespace nearby

internal/base/files.h

@@ -75,6 +75,11 @@ class Files {
   // determined.
   static std::optional<size_t> GetAvailableDiskSpaceInBytes(
       const FilePath& path);
+
+  // Returns true if the path is an absolute path.
+  // On Posix systems, this is a path that starts with a `/`.
+  // On Windows, this is a path that starts with a drive letter or a UNC path.
+  static bool IsAbsolutePath(const FilePath& path);
 };
 
 }  // namespace nearby

internal/base/files_test.cc

@@ -46,5 +46,21 @@ TEST(FilesTest, CreateHardLinkSuccess) {
   Files::RemoveFile(target);
 }
 
+#if defined(_WIN32)
+TEST(FilesTest, IsAbsolutePathWindows) {
+  EXPECT_TRUE(Files::IsAbsolutePath(FilePath("C:\\Users\\test\\file.txt")));
+  EXPECT_TRUE(Files::IsAbsolutePath(FilePath("\\\\server\\share\\file.txt")));
+  EXPECT_FALSE(Files::IsAbsolutePath(FilePath("file.txt")));
+  EXPECT_FALSE(Files::IsAbsolutePath(FilePath("C:Users\\test\\file.txt")));
+}
+#endif
+
+#if defined(__linux__) || defined(__APPLE__)
+TEST(FilesTest, IsAbsolutePathPosix) {
+  EXPECT_TRUE(Files::IsAbsolutePath(FilePath("/Users/test/file.txt")));
+  EXPECT_FALSE(Files::IsAbsolutePath(FilePath("file.txt")));
+}
+#endif
+
 }  // namespace
 }  // namespace nearby