1 files changed, 107 insertions, 0 deletions
diff --git a/src/buildtool/execution_api/local/file_storage.hpp b/src/buildtool/execution_api/local/file_storage.hpp
new file mode 100644
index 00000000..07ac1204
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+++ b/src/buildtool/execution_api/local/file_storage.hpp
@@ -0,0 +1,107 @@
+#ifndef INCLUDED_SRC_BUILDTOOL_EXECUTION_API_LOCAL_FILE_STORAGE_HPP
+#define INCLUDED_SRC_BUILDTOOL_EXECUTION_API_LOCAL_FILE_STORAGE_HPP
+
+#include <filesystem>
+#include <string>
+
+#include "src/buildtool/execution_api/common/execution_common.hpp"
+#include "src/buildtool/file_system/file_system_manager.hpp"
+
+enum class StoreMode {
+    // First thread to write conflicting file wins.
+    FirstWins,
+    // Last thread to write conflicting file wins, effectively overwriting
+    // existing entries. NOTE: This might cause races if hard linking from
+    // stored files due to an issue with the interaction of rename(2) and
+    // link(2) (see: https://stackoverflow.com/q/69076026/1107763).
+    LastWins
+};
+
+template <ObjectType kType = ObjectType::File,
+          StoreMode kMode = StoreMode::FirstWins>
+class FileStorage {
+  public:
+    explicit FileStorage(std::filesystem::path storage_root) noexcept
+        : storage_root_{std::move(storage_root)} {}
+
+    /// \brief Add file to storage.
+    /// \returns true if file exists afterward.
+    [[nodiscard]] auto AddFromFile(
+        std::string const& id,
+        std::filesystem::path const& source_path) const noexcept -> bool {
+        return AtomicAdd(id, source_path);
+    }
+
+    /// \brief Add bytes to storage.
+    /// \returns true if file exists afterward.
+    [[nodiscard]] auto AddFromBytes(std::string const& id,
+                                    std::string const& bytes) const noexcept
+        -> bool {
+        return AtomicAdd(id, bytes);
+    }
+
+    [[nodiscard]] auto GetPath(std::string const& name) const noexcept
+        -> std::filesystem::path {
+        return storage_root_ / name;
+    }
+
+  private:
+    std::filesystem::path const storage_root_{};
+
+    /// \brief Add file to storage via copy and atomic rename.
+    /// If a race-condition occurs, the winning thread will be the one
+    /// performing the rename operation first or last, depending on kMode being
+    /// set to FirstWins or LastWins, respectively. All threads will signal
+    /// success.
+    /// \returns true if file exists afterward.
+    template <class T>
+    [[nodiscard]] auto AtomicAdd(std::string const& id,
+                                 T const& data) const noexcept -> bool {
+        auto file_path = storage_root_ / id;
+        if (kMode == StoreMode::LastWins or
+            not FileSystemManager::Exists(file_path)) {
+            auto unique_path = CreateUniquePath(file_path);
+            if (unique_path and
+                FileSystemManager::CreateDirectory(file_path.parent_path()) and
+                CreateFileFromData(*unique_path, data) and
+                StageFile(*unique_path, file_path)) {
+                Logger::Log(
+                    LogLevel::Trace, "created entry {}.", file_path.string());
+                return true;
+            }
+        }
+        return FileSystemManager::IsFile(file_path);
+    }
+
+    /// \brief Create file from file path.
+    [[nodiscard]] static auto CreateFileFromData(
+        std::filesystem::path const& file_path,
+        std::filesystem::path const& other_path) noexcept -> bool {
+        return FileSystemManager::CopyFileAs<kType>(other_path, file_path);
+    }
+
+    /// \brief Create file from bytes.
+    [[nodiscard]] static auto CreateFileFromData(
+        std::filesystem::path const& file_path,
+        std::string const& bytes) noexcept -> bool {
+        return FileSystemManager::WriteFileAs<kType>(bytes, file_path);
+    }
+
+    /// \brief Stage file from source path to target path.
+    [[nodiscard]] static auto StageFile(
+        std::filesystem::path const& src_path,
+        std::filesystem::path const& dst_path) noexcept -> bool {
+        switch (kMode) {
+            case StoreMode::FirstWins:
+                // try rename source or delete it if the target already exists
+                return FileSystemManager::Rename(
+                           src_path, dst_path, /*no_clobber=*/true) or
+                       (FileSystemManager::IsFile(dst_path) and
+                        FileSystemManager::RemoveFile(src_path));
+            case StoreMode::LastWins:
+                return FileSystemManager::Rename(src_path, dst_path);
+        }
+    }
+};
+
+#endif  // INCLUDED_SRC_BUILDTOOL_EXECUTION_API_LOCAL_FILE_STORAGE_HPP