2 files changed, 115 insertions, 1 deletions

diff --git a/src/core/file_sys/archive_extsavedata.cpp b/src/core/file_sys/archive_extsavedata.cpp
index e1d29efd3..e1c4931ec 100644
--- a/src/core/file_sys/archive_extsavedata.cpp
+++ b/src/core/file_sys/archive_extsavedata.cpp
@@ -11,6 +11,9 @@
 #include "common/string_util.h"
 #include "core/file_sys/archive_extsavedata.h"
 #include "core/file_sys/disk_archive.h"
+#include "core/file_sys/errors.h"
+#include "core/file_sys/path_parser.h"
+#include "core/file_sys/savedata_archive.h"
 #include "core/hle/service/fs/archive.h"
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -18,6 +21,116 @@
 
 namespace FileSys {
 
+/**
+ * A modified version of DiskFile for fixed-size file used by ExtSaveData
+ * The file size can't be changed by SetSize or Write.
+ */
+class FixSizeDiskFile : public DiskFile {
+public:
+    FixSizeDiskFile(FileUtil::IOFile&& file, const Mode& mode) : DiskFile(std::move(file), mode) {
+        size = GetSize();
+    }
+
+    bool SetSize(u64 size) const override {
+        return false;
+    }
+
+    ResultVal<size_t> Write(u64 offset, size_t length, bool flush,
+                            const u8* buffer) const override {
+        if (offset > size) {
+            return ResultCode(ErrorDescription::FS_WriteBeyondEnd, ErrorModule::FS,
+                              ErrorSummary::InvalidArgument, ErrorLevel::Usage);
+        } else if (offset == size) {
+            return MakeResult<size_t>(0);
+        }
+
+        if (offset + length > size) {
+            length = size - offset;
+        }
+
+        return DiskFile::Write(offset, length, flush, buffer);
+    }
+
+private:
+    u64 size{};
+};
+
+/**
+ * Archive backend for general extsave data archive type.
+ * The behaviour of ExtSaveDataArchive is almost the same as SaveDataArchive, except for
+ *  - file size can't be changed once created (thus creating zero-size file and openning with create
+ *    flag are prohibited);
+ *  - always open a file with read+write permission.
+ */
+class ExtSaveDataArchive : public SaveDataArchive {
+public:
+    ExtSaveDataArchive(const std::string& mount_point) : SaveDataArchive(mount_point) {}
+
+    std::string GetName() const override {
+        return "ExtSaveDataArchive: " + mount_point;
+    }
+
+    ResultVal<std::unique_ptr<FileBackend>> OpenFile(const Path& path,
+                                                     const Mode& mode) const override {
+        LOG_DEBUG(Service_FS, "called path=%s mode=%01X", path.DebugStr().c_str(), mode.hex);
+
+        const PathParser path_parser(path);
+
+        if (!path_parser.IsValid()) {
+            LOG_ERROR(Service_FS, "Invalid path %s", path.DebugStr().c_str());
+            return ERROR_INVALID_PATH;
+        }
+
+        if (mode.hex == 0) {
+            LOG_ERROR(Service_FS, "Empty open mode");
+            return ERROR_UNSUPPORTED_OPEN_FLAGS;
+        }
+
+        if (mode.create_flag) {
+            LOG_ERROR(Service_FS, "Create flag is not supported");
+            return ERROR_UNSUPPORTED_OPEN_FLAGS;
+        }
+
+        const auto full_path = path_parser.BuildHostPath(mount_point);
+
+        switch (path_parser.GetHostStatus(mount_point)) {
+        case PathParser::InvalidMountPoint:
+            LOG_CRITICAL(Service_FS, "(unreachable) Invalid mount point %s", mount_point.c_str());
+            return ERROR_FILE_NOT_FOUND;
+        case PathParser::PathNotFound:
+            LOG_ERROR(Service_FS, "Path not found %s", full_path.c_str());
+            return ERROR_PATH_NOT_FOUND;
+        case PathParser::FileInPath:
+        case PathParser::DirectoryFound:
+            LOG_ERROR(Service_FS, "Unexpected file or directory in %s", full_path.c_str());
+            return ERROR_UNEXPECTED_FILE_OR_DIRECTORY;
+        case PathParser::NotFound:
+            LOG_ERROR(Service_FS, "%s not found", full_path.c_str());
+            return ERROR_FILE_NOT_FOUND;
+        }
+
+        FileUtil::IOFile file(full_path, "r+b");
+        if (!file.IsOpen()) {
+            LOG_CRITICAL(Service_FS, "(unreachable) Unknown error opening %s", full_path.c_str());
+            return ERROR_FILE_NOT_FOUND;
+        }
+
+        Mode rwmode;
+        rwmode.write_flag.Assign(1);
+        rwmode.read_flag.Assign(1);
+        auto disk_file = std::make_unique<FixSizeDiskFile>(std::move(file), rwmode);
+        return MakeResult<std::unique_ptr<FileBackend>>(std::move(disk_file));
+    }
+
+    ResultCode CreateFile(const Path& path, u64 size) const override {
+        if (size == 0) {
+            LOG_ERROR(Service_FS, "Zero-size file is not supported");
+            return ERROR_UNSUPPORTED_OPEN_FLAGS;
+        }
+        return SaveDataArchive::CreateFile(path, size);
+    }
+};
+
 std::string GetExtSaveDataPath(const std::string& mount_point, const Path& path) {
     std::vector<u8> vec_data = path.AsBinary();
     const u32* data = reinterpret_cast<const u32*>(vec_data.data());
@@ -84,7 +197,7 @@ ResultVal<std::unique_ptr<ArchiveBackend>> ArchiveFactory_ExtSaveData::Open(cons
                               ErrorSummary::InvalidState, ErrorLevel::Status);
         }
     }
-    auto archive = std::make_unique<DiskArchive>(fullpath);
+    auto archive = std::make_unique<ExtSaveDataArchive>(fullpath);
     return MakeResult<std::unique_ptr<ArchiveBackend>>(std::move(archive));
 }
 
diff --git a/src/core/hle/result.h b/src/core/hle/result.h
index 8330894f2..a355f970a 100644
--- a/src/core/hle/result.h
+++ b/src/core/hle/result.h
@@ -34,6 +34,7 @@ enum class ErrorDescription : u32 {
         513, // TODO(purpasmart): Check if this name fits its actual usage
     GPU_FirstInitialization = 519,
     FS_InvalidPath = 702,
+    FS_WriteBeyondEnd = 705,
     FS_UnsupportedOpenFlags = 760,
     FS_UnexpectedFileOrDirectory = 770,
     InvalidSection = 1000,