DiscIO: Add support for CleanRip-style split ISOs.

Source/Core/DiscIO/SplitFileBlob.cpp

@@ -0,0 +1,90 @@
+// Copyright 2023 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "DiscIO/SplitFileBlob.h"
+
+#include <memory>
+#include <string>
+#include <string_view>
+#include <vector>
+
+#include <fmt/format.h>
+
+#include "Common/Assert.h"
+#include "Common/FileUtil.h"
+#include "Common/IOFile.h"
+#include "Common/MsgHandler.h"
+
+namespace DiscIO
+{
+SplitPlainFileReader::SplitPlainFileReader(std::vector<SingleFile> files)
+    : m_files(std::move(files))
+{
+  m_size = 0;
+  for (const auto& f : m_files)
+    m_size += f.size;
+}
+
+std::unique_ptr<SplitPlainFileReader> SplitPlainFileReader::Create(std::string_view first_file_path)
+{
+  constexpr std::string_view part0_iso = ".part0.iso";
+  if (!first_file_path.ends_with(part0_iso))
+    return nullptr;
+
+  const std::string_view base_path =
+      first_file_path.substr(0, first_file_path.size() - part0_iso.size());
+  std::vector<SingleFile> files;
+  size_t index = 0;
+  u64 offset = 0;
+  while (true)
+  {
+    File::IOFile f(fmt::format("{}.part{}.iso", base_path, index), "rb");
+    if (!f.IsOpen())
+      break;
+    const u64 size = f.GetSize();
+    if (size == 0)
+      return nullptr;
+    files.emplace_back(SingleFile{std::move(f), offset, size});
+    offset += size;
+    ++index;
+  }
+
+  if (files.size() < 2)
+    return nullptr;
+
+  files.shrink_to_fit();
+  return std::unique_ptr<SplitPlainFileReader>(new SplitPlainFileReader(std::move(files)));
+}
+
+bool SplitPlainFileReader::Read(u64 offset, u64 nbytes, u8* out_ptr)
+{
+  if (offset >= m_size)
+    return false;
+
+  u64 current_offset = offset;
+  u64 rest = nbytes;
+  u8* out = out_ptr;
+  for (auto& file : m_files)
+  {
+    if (current_offset >= file.offset && current_offset < file.offset + file.size)
+    {
+      auto& f = file.file;
+      const u64 seek_offset = current_offset - file.offset;
+      const u64 current_read = std::min(file.size - seek_offset, rest);
+      if (!f.Seek(seek_offset, File::SeekOrigin::Begin) || !f.ReadBytes(out, current_read))
+      {
+        f.ClearError();
+        return false;
+      }
+
+      rest -= current_read;
+      if (rest == 0)
+        return true;
+      current_offset += current_read;
+      out += current_read;
+    }
+  }
+
+  return rest == 0;
+}
+}  // namespace DiscIO