GCMemcard: Implement utility functions to read saves from and write s…

…aves to files, without involving a memory card.

Source/Core/Core/HW/GCMemcard/GCMemcard.h

@@ -400,6 +400,12 @@ static_assert(sizeof(BlockAlloc) == BLOCK_SIZE);
 static_assert(std::is_trivially_copyable_v<BlockAlloc>);
 #pragma pack(pop)
 
+struct Savefile
+{
+  DEntry dir_entry;
+  std::vector<GCMBlock> blocks;
+};
+
 class GCMemcard
 {
 private:

Source/Core/Core/HW/GCMemcard/GCMemcardUtils.cpp

@@ -1,9 +1,25 @@
 #include "Core/HW/GCMemcard/GCMemcardUtils.h"
 
+#include <array>
+#include <string>
+#include <vector>
+
+#include "Common/CommonTypes.h"
+#include "Common/IOFile.h"
+
 #include "Core/HW/GCMemcard/GCMemcard.h"
 
 namespace Memcard
 {
+constexpr u32 GCI_HEADER_SIZE = DENTRY_SIZE;
+constexpr std::array<u8, 12> SAV_MAGIC = {0x44, 0x41, 0x54, 0x45, 0x4C, 0x47,
+                                          0x43, 0x5F, 0x53, 0x41, 0x56, 0x45};  // "DATELGC_SAVE"
+constexpr u32 SAV_HEADER_SIZE = 0xC0;
+constexpr u32 SAV_DENTRY_OFFSET = 0x80;
+constexpr std::array<u8, 6> GCS_MAGIC = {0x47, 0x43, 0x53, 0x41, 0x56, 0x45};  // "GCSAVE"
+constexpr u32 GCS_HEADER_SIZE = 0x150;
+constexpr u32 GCS_DENTRY_OFFSET = 0x110;
+
 bool HasSameIdentity(const DEntry& lhs, const DEntry& rhs)
 {
   // The Gamecube BIOS identifies two files as being 'the same' (that is, disallows copying from one
@@ -53,4 +69,218 @@ bool HasSameIdentity(const DEntry& lhs, const DEntry& rhs)
 
   return true;
 }
+
+static void ByteswapDEntrySavHeader(std::array<u8, DENTRY_SIZE>& entry)
+{
+  // several bytes in SAV are swapped compared to the internal memory card format
+  for (size_t p : {0x06, 0x2C, 0x2E, 0x30, 0x32, 0x34, 0x36, 0x38, 0x3A, 0x3C, 0x3E})
+    std::swap(entry[p], entry[p + 1]);
+}
+
+static DEntry ExtractDEntryFromSavHeader(const std::array<u8, SAV_HEADER_SIZE>& sav_header)
+{
+  std::array<u8, DENTRY_SIZE> entry;
+  std::memcpy(entry.data(), &sav_header[SAV_DENTRY_OFFSET], DENTRY_SIZE);
+  ByteswapDEntrySavHeader(entry);
+
+  DEntry dir_entry;
+  std::memcpy(&dir_entry, entry.data(), DENTRY_SIZE);
+  return dir_entry;
+}
+
+static void InjectDEntryToSavHeader(std::array<u8, SAV_HEADER_SIZE>& sav_header,
+                                    const DEntry& dir_entry)
+{
+  std::array<u8, DENTRY_SIZE> entry;
+  std::memcpy(entry.data(), &dir_entry, DENTRY_SIZE);
+  ByteswapDEntrySavHeader(entry);
+  std::memcpy(&sav_header[SAV_DENTRY_OFFSET], entry.data(), DENTRY_SIZE);
+}
+
+static bool ReadBlocksFromIOFile(File::IOFile& file, std::vector<GCMBlock>& blocks,
+                                 size_t block_count)
+{
+  blocks.reserve(block_count);
+  for (size_t i = 0; i < block_count; ++i)
+  {
+    GCMBlock& block = blocks.emplace_back();
+    if (!file.ReadBytes(block.m_block.data(), block.m_block.size()))
+      return false;
+  }
+  return true;
+}
+
+static std::variant<ReadSavefileErrorCode, Savefile> ReadSavefileInternalGCI(File::IOFile& file,
+                                                                             u64 filesize)
+{
+  Savefile savefile;
+  if (!file.ReadBytes(&savefile.dir_entry, DENTRY_SIZE))
+    return ReadSavefileErrorCode::IOError;
+
+  const size_t block_count = savefile.dir_entry.m_block_count;
+  const u64 expected_size = DENTRY_SIZE + block_count * BLOCK_SIZE;
+  if (expected_size != filesize)
+    return ReadSavefileErrorCode::DataCorrupted;
+
+  if (!ReadBlocksFromIOFile(file, savefile.blocks, block_count))
+    return ReadSavefileErrorCode::IOError;
+
+  return savefile;
+}
+
+static std::variant<ReadSavefileErrorCode, Savefile> ReadSavefileInternalGCS(File::IOFile& file,
+                                                                             u64 filesize)
+{
+  std::array<u8, GCS_HEADER_SIZE> gcs_header;
+  if (!file.ReadBytes(gcs_header.data(), gcs_header.size()))
+    return ReadSavefileErrorCode::IOError;
+
+  if (std::memcmp(gcs_header.data(), GCS_MAGIC.data(), GCS_MAGIC.size()) != 0)
+    return ReadSavefileErrorCode::DataCorrupted;
+
+  Savefile savefile;
+  std::memcpy(&savefile.dir_entry, &gcs_header[GCS_DENTRY_OFFSET], DENTRY_SIZE);
+
+  // field containing the Block count as displayed within
+  // the GameSaves software is not stored in the GCS file.
+  // It is stored only within the corresponding GSV file.
+  // If the GCS file is added without using the GameSaves software,
+  // the value stored is always "1"
+
+  // to get the actual block count calculate backwards from the filesize
+  const u64 total_block_size = filesize - GCS_HEADER_SIZE;
+  if ((total_block_size % BLOCK_SIZE) != 0)
+    return ReadSavefileErrorCode::DataCorrupted;
+
+  const size_t block_count = total_block_size / BLOCK_SIZE;
+  savefile.dir_entry.m_block_count = static_cast<u16>(block_count);
+
+  if (!ReadBlocksFromIOFile(file, savefile.blocks, block_count))
+    return ReadSavefileErrorCode::IOError;
+
+  return savefile;
+}
+
+static std::variant<ReadSavefileErrorCode, Savefile> ReadSavefileInternalSAV(File::IOFile& file,
+                                                                             u64 filesize)
+{
+  std::array<u8, SAV_HEADER_SIZE> sav_header;
+  if (!file.ReadBytes(sav_header.data(), sav_header.size()))
+    return ReadSavefileErrorCode::IOError;
+
+  if (std::memcmp(sav_header.data(), SAV_MAGIC.data(), SAV_MAGIC.size()) != 0)
+    return ReadSavefileErrorCode::DataCorrupted;
+
+  Savefile savefile;
+  savefile.dir_entry = ExtractDEntryFromSavHeader(sav_header);
+
+  const size_t block_count = savefile.dir_entry.m_block_count;
+  const u64 expected_size = SAV_HEADER_SIZE + block_count * BLOCK_SIZE;
+  if (expected_size != filesize)
+    return ReadSavefileErrorCode::DataCorrupted;
+
+  if (!ReadBlocksFromIOFile(file, savefile.blocks, block_count))
+    return ReadSavefileErrorCode::IOError;
+
+  return savefile;
+}
+
+std::variant<ReadSavefileErrorCode, Savefile> ReadSavefile(const std::string& filename)
+{
+  File::IOFile file(filename, "rb");
+  if (!file)
+    return ReadSavefileErrorCode::OpenFileFail;
+
+  // Since GCI, GCS and SAV all have different header lengths but the block size is always the same,
+  // we can detect the type from the filesize.
+  const u64 filesize = file.GetSize();
+  const u64 header_size = filesize % BLOCK_SIZE;
+
+  switch (header_size)
+  {
+  case GCI_HEADER_SIZE:
+    return ReadSavefileInternalGCI(file, filesize);
+  case GCS_HEADER_SIZE:
+    return ReadSavefileInternalGCS(file, filesize);
+  case SAV_HEADER_SIZE:
+    return ReadSavefileInternalSAV(file, filesize);
+  default:
+    return ReadSavefileErrorCode::DataCorrupted;
+  }
+}
+
+static bool WriteSavefileInternalGCI(File::IOFile& file, const Savefile& savefile)
+{
+  if (!file.WriteBytes(&savefile.dir_entry, DENTRY_SIZE))
+    return false;
+
+  for (const GCMBlock& block : savefile.blocks)
+  {
+    if (!file.WriteBytes(block.m_block.data(), block.m_block.size()))
+      return false;
+  }
+
+  return file.IsGood();
+}
+
+static bool WriteSavefileInternalGCS(File::IOFile& file, const Savefile& savefile)
+{
+  std::array<u8, GCS_HEADER_SIZE> header;
+  std::memset(header.data(), 0, header.size());
+  std::memcpy(header.data(), GCS_MAGIC.data(), GCS_MAGIC.size());
+
+  DEntry gcs_entry = savefile.dir_entry;
+  gcs_entry.m_block_count = 1;  // always stored as 1 in GCS files
+  std::memcpy(&header[GCS_DENTRY_OFFSET], &gcs_entry, DENTRY_SIZE);
+
+  if (!file.WriteBytes(header.data(), header.size()))
+    return false;
+
+  for (const GCMBlock& block : savefile.blocks)
+  {
+    if (!file.WriteBytes(block.m_block.data(), block.m_block.size()))
+      return false;
+  }
+
+  return file.IsGood();
+}
+
+static bool WriteSavefileInternalSAV(File::IOFile& file, const Savefile& savefile)
+{
+  std::array<u8, SAV_HEADER_SIZE> header;
+  std::memset(header.data(), 0, header.size());
+  std::memcpy(header.data(), SAV_MAGIC.data(), SAV_MAGIC.size());
+
+  InjectDEntryToSavHeader(header, savefile.dir_entry);
+
+  if (!file.WriteBytes(header.data(), header.size()))
+    return false;
+
+  for (const GCMBlock& block : savefile.blocks)
+  {
+    if (!file.WriteBytes(block.m_block.data(), block.m_block.size()))
+      return false;
+  }
+
+  return file.IsGood();
+}
+
+bool WriteSavefile(const std::string& filename, const Savefile& savefile, SavefileFormat format)
+{
+  File::IOFile file(filename, "wb");
+  if (!file)
+    return false;
+
+  switch (format)
+  {
+  case SavefileFormat::GCI:
+    return WriteSavefileInternalGCI(file, savefile);
+  case SavefileFormat::GCS:
+    return WriteSavefileInternalGCS(file, savefile);
+  case SavefileFormat::SAV:
+    return WriteSavefileInternalSAV(file, savefile);
+  default:
+    return false;
+  }
+}
 }  // namespace Memcard

Source/Core/Core/HW/GCMemcard/GCMemcardUtils.h

@@ -4,9 +4,33 @@
 
 #pragma once
 
+#include <string>
+#include <variant>
+
+#include "Core/HW/GCMemcard/GCMemcard.h"
+
 namespace Memcard
 {
-struct DEntry;
-
 bool HasSameIdentity(const DEntry& lhs, const DEntry& rhs);
+
+enum class ReadSavefileErrorCode
+{
+  OpenFileFail,
+  IOError,
+  DataCorrupted,
+};
+
+// Reads a Gamecube memory card savefile from a file.
+// Supported formats are GCI, GCS (Gameshark), and SAV (MaxDrive).
+std::variant<ReadSavefileErrorCode, Savefile> ReadSavefile(const std::string& filename);
+
+enum class SavefileFormat
+{
+  GCI,
+  GCS,
+  SAV,
+};
+
+// Writes a Gamecube memory card savefile to a file.
+bool WriteSavefile(const std::string& filename, const Savefile& savefile, SavefileFormat format);
 }  // namespace Memcard