Add initial WiiConnect24 support

Source/Core/Common/Crypto/AES.cpp

@@ -408,4 +408,21 @@ std::unique_ptr<Context> CreateContextDecrypt(const u8* key)
   return CreateContext<Mode::Decrypt>(key);
 }
 
+// OFB encryption and decryption are the exact same. We don't encrypt though.
+void CryptOFB(const u8* key, const u8* iv, u8* iv_out, const u8* buf_in, u8* buf_out, size_t size)
+{
+  mbedtls_aes_context aes_ctx;
+  size_t iv_offset = 0;
+
+  std::array<u8, 16> iv_tmp{};
+  if (iv)
+    std::memcpy(&iv_tmp[0], iv, 16);
+
+  ASSERT(!mbedtls_aes_setkey_enc(&aes_ctx, key, 128));
+  mbedtls_aes_crypt_ofb(&aes_ctx, size, &iv_offset, &iv_tmp[0], buf_in, buf_out);
+
+  if (iv_out)
+    std::memcpy(iv_out, &iv_tmp[0], 16);
+}
+
 }  // namespace Common::AES

Source/Core/Common/Crypto/AES.h

@@ -46,4 +46,7 @@ public:
 std::unique_ptr<Context> CreateContextEncrypt(const u8* key);
 std::unique_ptr<Context> CreateContextDecrypt(const u8* key);
 
+// OFB decryption for WiiConnect24
+void CryptOFB(const u8* key, const u8* iv, u8* iv_out, const u8* buf_in, u8* buf_out, size_t size);
+
 }  // namespace Common::AES

Source/Core/Core/CMakeLists.txt

@@ -360,6 +360,11 @@ add_library(core
   IOS/Network/KD/NetKDTime.h
   IOS/Network/KD/NWC24Config.cpp
   IOS/Network/KD/NWC24Config.h
+  IOS/Network/KD/NWC24DL.cpp
+  IOS/Network/KD/NWC24DL.h
+  IOS/Network/KD/VFF/VFFUtil.cpp
+  IOS/Network/KD/VFF/VFFUtil.h
+  IOS/Network/KD/WC24File.h
   IOS/Network/MACUtils.cpp
   IOS/Network/MACUtils.h
   IOS/Network/NCD/Manage.cpp
@@ -595,6 +600,7 @@ PUBLIC
   videosoftware
 
 PRIVATE
+  FatFs
   fmt::fmt
   ${LZO}
   ZLIB::ZLIB

Source/Core/Core/IOS/Network/KD/NWC24Config.h

@@ -19,6 +19,14 @@ enum ErrorCode : s32
 {
   WC24_OK = 0,
   WC24_ERR_FATAL = -1,
+  WC24_ERR_NOT_FOUND = -13,
+  WC24_ERR_BROKEN = -14,
+  WC24_ERR_FILE_OPEN = -16,
+  WC24_ERR_FILE_CLOSE = -17,
+  WC24_ERR_FILE_READ = -18,
+  WC24_ERR_FILE_WRITE = -19,
+  WC24_ERR_NETWORK = -31,
+  WC24_ERR_SERVER = -32,
   WC24_ERR_ID_NONEXISTANCE = -34,
   WC24_ERR_ID_GENERATED = -35,
   WC24_ERR_ID_REGISTERED = -36,

Source/Core/Core/IOS/Network/KD/NWC24DL.cpp

@@ -0,0 +1,143 @@
+// Copyright 2022 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "Core/IOS/Network/KD/NWC24DL.h"
+
+#include "Common/BitUtils.h"
+#include "Common/CommonPaths.h"
+#include "Common/CommonTypes.h"
+#include "Common/Logging/Log.h"
+#include "Common/Swap.h"
+#include "Core/IOS/FS/FileSystem.h"
+#include "Core/IOS/Uids.h"
+
+namespace IOS::HLE::NWC24
+{
+constexpr const char DL_LIST_PATH[] = "/" WII_WC24CONF_DIR "/nwc24dl.bin";
+
+NWC24Dl::NWC24Dl(std::shared_ptr<FS::FileSystem> fs) : m_fs{std::move(fs)}
+{
+  ReadDlList();
+}
+
+void NWC24Dl::ReadDlList()
+{
+  const auto file = m_fs->OpenFile(PID_KD, PID_KD, DL_LIST_PATH, FS::Mode::Read);
+  if (!file || !file->Read(&m_data, 1))
+    return;
+
+  const s32 file_error = CheckNwc24DlList();
+  if (file_error)
+    ERROR_LOG_FMT(IOS_WC24, "There is an error in the DL list for WC24: {}", file_error);
+}
+
+s32 NWC24Dl::CheckNwc24DlList() const
+{
+  // 'WcDl' magic
+  if (Magic() != DL_LIST_MAGIC)
+  {
+    ERROR_LOG_FMT(IOS_WC24, "DL list magic mismatch");
+    return -1;
+  }
+
+  if (Version() != 1)
+  {
+    ERROR_LOG_FMT(IOS_WC24, "DL list version mismatch");
+    return -1;
+  }
+
+  return 0;
+}
+
+void NWC24Dl::WriteDlList() const
+{
+  constexpr FS::Modes public_modes{FS::Mode::ReadWrite, FS::Mode::ReadWrite, FS::Mode::ReadWrite};
+  m_fs->CreateFullPath(PID_KD, PID_KD, DL_LIST_PATH, 0, public_modes);
+  const auto file = m_fs->CreateAndOpenFile(PID_KD, PID_KD, DL_LIST_PATH, public_modes);
+
+  if (!file || !file->Write(&m_data, 1))
+    ERROR_LOG_FMT(IOS_WC24, "Failed to open or write WC24 DL list file");
+}
+
+bool NWC24Dl::DoesEntryExist(u16 entry_index)
+{
+  return m_data.entries[entry_index].low_title_id != 0;
+}
+
+std::string NWC24Dl::GetDownloadURL(u16 entry_index, std::optional<u8> subtask_id) const
+{
+  std::string url(m_data.entries[entry_index].dl_url);
+
+  // Determine if we need to append the subtask to the URL.
+  if (subtask_id &&
+      Common::ExtractBit(Common::swap32(m_data.entries[entry_index].subtask_bitmask), 1))
+  {
+    url.append(fmt::format(".{:02d}", *subtask_id));
+  }
+
+  return url;
+}
+
+std::string NWC24Dl::GetVFFContentName(u16 entry_index, std::optional<u8> subtask_id) const
+{
+  std::string content(m_data.entries[entry_index].filename);
+
+  // Determine if we need to append the subtask to the name.
+  if (subtask_id &&
+      Common::ExtractBit(Common::swap32(m_data.entries[entry_index].subtask_bitmask), 0))
+  {
+    content.append(fmt::format(".{:02d}", *subtask_id));
+  }
+
+  return content;
+}
+
+std::string NWC24Dl::GetVFFPath(u16 entry_index) const
+{
+  const u32 lower_title_id = Common::swap32(m_data.entries[entry_index].low_title_id);
+  const u32 high_title_id = Common::swap32(m_data.entries[entry_index].high_title_id);
+
+  return fmt::format("/title/{0:08x}/{1:08x}/data/wc24dl.vff", lower_title_id, high_title_id);
+}
+
+WC24PubkMod NWC24Dl::GetWC24PubkMod(u16 entry_index) const
+{
+  WC24PubkMod pubkMod;
+  const u32 lower_title_id = Common::swap32(m_data.entries[entry_index].low_title_id);
+  const u32 high_title_id = Common::swap32(m_data.entries[entry_index].high_title_id);
+
+  const std::string path =
+      fmt::format("/title/{0:08x}/{1:08x}/data/wc24pubk.mod", lower_title_id, high_title_id);
+
+  const auto file = m_fs->OpenFile(PID_KD, PID_KD, path, IOS::HLE::FS::Mode::Read);
+  file->Read(&pubkMod, 1);
+
+  return pubkMod;
+}
+
+bool NWC24Dl::IsEncrypted(u16 entry_index) const
+{
+  return !!Common::ExtractBit(Common::swap32(m_data.entries[entry_index].flags), 3);
+}
+
+u32 NWC24Dl::Magic() const
+{
+  return Common::swap32(m_data.header.magic);
+}
+
+void NWC24Dl::SetMagic(u32 magic)
+{
+  m_data.header.magic = Common::swap32(magic);
+}
+
+u32 NWC24Dl::Version() const
+{
+  return Common::swap32(m_data.header.version);
+}
+
+void NWC24Dl::SetVersion(u32 version)
+{
+  m_data.header.version = Common::swap32(version);
+}
+
+}  // namespace IOS::HLE::NWC24

Source/Core/Core/IOS/Network/KD/NWC24DL.h

@@ -0,0 +1,123 @@
+// Copyright 2022 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <memory>
+#include <optional>
+#include <string>
+#include "Common/CommonTypes.h"
+#include "Core/IOS/Network/KD/WC24File.h"
+
+namespace IOS::HLE
+{
+namespace FS
+{
+class FileSystem;
+}
+namespace NWC24
+{
+class NWC24Dl final
+{
+public:
+  explicit NWC24Dl(std::shared_ptr<FS::FileSystem> fs);
+
+  void ReadDlList();
+  void WriteDlList() const;
+
+  s32 CheckNwc24DlList() const;
+
+  bool DoesEntryExist(u16 entry_index);
+  bool IsEncrypted(u16 entry_index) const;
+  std::string GetVFFContentName(u16 entry_index, std::optional<u8> subtask_id) const;
+  std::string GetDownloadURL(u16 entry_index, std::optional<u8> subtask_id) const;
+  std::string GetVFFPath(u16 entry_index) const;
+  WC24PubkMod GetWC24PubkMod(u16 entry_index) const;
+
+  u32 Magic() const;
+  void SetMagic(u32 magic);
+
+  u32 Version() const;
+  void SetVersion(u32 version);
+
+  static constexpr u32 MAX_ENTRIES = 120;
+
+private:
+  static constexpr u32 DL_LIST_MAGIC = 0x5763446C;  // WcDl
+  static constexpr u32 MAX_SUBENTRIES = 32;
+
+  enum EntryType : u8
+  {
+    UNK = 1,
+    MAIL,
+    CHANNEL_CONTENT,
+    UNUSED = 0xff
+  };
+
+#pragma pack(push, 1)
+  // The following format is partially based off of https://wiibrew.org/wiki//dev/net/kd/request.
+  struct DLListHeader final
+  {
+    u32 magic;    // 'WcDl' 0x5763446c
+    u32 version;  // must be 1
+    u32 unk1;
+    u32 unk2;
+    u16 max_subentries;  // Asserted to be less than max_entries
+    u16 reserved_mailnum;
+    u16 max_entries;
+    u8 reserved[106];
+  };
+
+  struct DLListRecord final
+  {
+    u32 low_title_id;
+    u32 next_dl_timestamp;
+    u32 last_modified_timestamp;
+    u8 flags;
+    u8 padding[3];
+  };
+
+  struct DLListEntry final
+  {
+    u16 index;
+    EntryType type;
+    u8 record_flags;
+    u32 flags;
+    u32 high_title_id;
+    u32 low_title_id;
+    u32 unknown1;
+    u16 group_id;
+    u16 padding1;
+    u16 remaining_downloads;
+    u16 error_count;
+    u16 dl_frequency;
+    u16 dl_frequency_when_err;
+    s32 error_code;
+    u8 subtask_id;
+    u8 subtask_type;
+    u8 subtask_flags;
+    u8 padding2;
+    u32 subtask_bitmask;
+    s32 unknown2;
+    u32 dl_timestamp;  // Last DL time
+    u32 subtask_timestamps[32];
+    char dl_url[236];
+    char filename[64];
+    u8 unk6[29];
+    u8 should_use_rootca;
+    u16 unknown3;
+  };
+
+  struct DLList final
+  {
+    DLListHeader header;
+    DLListRecord records[MAX_ENTRIES];
+    DLListEntry entries[MAX_ENTRIES];
+  };
+#pragma pack(pop)
+
+  std::shared_ptr<FS::FileSystem> m_fs;
+  DLList m_data;
+};
+}  // namespace NWC24
+}  // namespace IOS::HLE

Source/Core/Core/IOS/Network/KD/NetKDRequest.cpp

@@ -9,6 +9,7 @@
 #include <string_view>
 #include <utility>
 
+#include "Common/BitUtils.h"
 #include "Common/CommonPaths.h"
 #include "Common/CommonTypes.h"
 #include "Common/FileUtil.h"
@@ -19,6 +20,7 @@
 #include "Core/CommonTitles.h"
 #include "Core/HW/Memmap.h"
 #include "Core/IOS/FS/FileSystem.h"
+#include "Core/IOS/Network/KD/VFF/VFFUtil.h"
 #include "Core/IOS/Network/Socket.h"
 #include "Core/IOS/Uids.h"
 
@@ -145,8 +147,15 @@ s32 NWC24MakeUserID(u64* nwc24_id, u32 hollywood_id, u16 id_ctr, HardwareModel h
 }  // Anonymous namespace
 
 NetKDRequestDevice::NetKDRequestDevice(Kernel& ios, const std::string& device_name)
-    : Device(ios, device_name), config{ios.GetFS()}
+    : Device(ios, device_name), config{ios.GetFS()}, m_dl_list{ios.GetFS()}
 {
+  m_work_queue.Reset([this](AsyncTask task) {
+    const IPCReply reply = task.handler();
+    {
+      std::lock_guard lg(m_async_reply_lock);
+      m_async_replies.emplace(AsyncReply{task.request, reply.return_value});
+    }
+  });
 }
 
 NetKDRequestDevice::~NetKDRequestDevice()
@@ -154,6 +163,133 @@ NetKDRequestDevice::~NetKDRequestDevice()
   WiiSockMan::GetInstance().Clean();
 }
 
+void NetKDRequestDevice::Update()
+{
+  {
+    std::lock_guard lg(m_async_reply_lock);
+    while (!m_async_replies.empty())
+    {
+      const auto& reply = m_async_replies.front();
+      GetIOS()->EnqueueIPCReply(reply.request, reply.return_value);
+      m_async_replies.pop();
+    }
+  }
+}
+
+NWC24::ErrorCode NetKDRequestDevice::KDDownload(const u16 entry_index,
+                                                const std::optional<u8> subtask_id)
+{
+  std::vector<u8> file_data;
+
+  // Content metadata
+  const std::string content_name = m_dl_list.GetVFFContentName(entry_index, subtask_id);
+  const std::string url = m_dl_list.GetDownloadURL(entry_index, subtask_id);
+
+  INFO_LOG_FMT(IOS_WC24, "NET_KD_REQ: IOCTL_NWC24_DOWNLOAD_NOW_EX - NI - URL: {}", url);
+
+  INFO_LOG_FMT(IOS_WC24, "NET_KD_REQ: IOCTL_NWC24_DOWNLOAD_NOW_EX - NI - Name: {}", content_name);
+
+  const Common::HttpRequest::Response response = m_http.Get(url);
+
+  if (!response)
+  {
+    ERROR_LOG_FMT(IOS_WC24, "Failed to request data at {}", url);
+    return NWC24::WC24_ERR_SERVER;
+  }
+
+  // Check if the filesize is smaller than the header size.
+  if (response->size() < sizeof(NWC24::WC24File))
+  {
+    ERROR_LOG_FMT(IOS_WC24, "File at {} is too small to be a valid file.", url);
+    return NWC24::WC24_ERR_BROKEN;
+  }
+
+  // Now we read the file
+  NWC24::WC24File wc24File;
+  std::memcpy(&wc24File, response->data(), sizeof(NWC24::WC24File));
+
+  std::vector<u8> temp_buffer(response->begin() + 320, response->end());
+
+  if (m_dl_list.IsEncrypted(entry_index))
+  {
+    NWC24::WC24PubkMod pubkMod = m_dl_list.GetWC24PubkMod(entry_index);
+
+    file_data = std::vector<u8>(response->size() - 320);
+
+    Common::AES::CryptOFB(pubkMod.aes_key, wc24File.iv, wc24File.iv, temp_buffer.data(),
+                          file_data.data(), temp_buffer.size());
+  }
+  else
+  {
+    file_data = std::move(temp_buffer);
+  }
+
+  NWC24::ErrorCode reply = IOS::HLE::NWC24::OpenVFF(m_dl_list.GetVFFPath(entry_index), content_name,
+                                                    m_ios.GetFS(), file_data);
+
+  return reply;
+}
+
+IPCReply NetKDRequestDevice::HandleNWC24DownloadNowEx(const IOCtlRequest& request)
+{
+  const u32 flags = Memory::Read_U32(request.buffer_in);
+  // Nintendo converts the entry ID between a u32 and u16
+  // several times, presumably for alignment purposes.
+  // We'll skip past buffer_in+4 and keep the entry index as a u16.
+  const u16 entry_index = Memory::Read_U16(request.buffer_in + 6);
+  const u32 subtask_bitmask = Memory::Read_U32(request.buffer_in + 8);
+
+  INFO_LOG_FMT(IOS_WC24,
+               "NET_KD_REQ: IOCTL_NWC24_DOWNLOAD_NOW_EX - NI - flags: {}, index: {}, bitmask: {}",
+               flags, entry_index, subtask_bitmask);
+
+  if (entry_index >= NWC24::NWC24Dl::MAX_ENTRIES)
+  {
+    ERROR_LOG_FMT(IOS_WC24, "NET_KD_REQ: Entry index out of range.");
+    WriteReturnValue(NWC24::WC24_ERR_BROKEN, request.buffer_out);
+    return IPCReply(NWC24::WC24_ERR_BROKEN);
+  }
+
+  if (!m_dl_list.DoesEntryExist(entry_index))
+  {
+    ERROR_LOG_FMT(IOS_WC24, "NET_KD_REQ: Requested entry does not exist in download list!");
+    WriteReturnValue(NWC24::WC24_ERR_NOT_FOUND, request.buffer_out);
+    return IPCReply(NWC24::WC24_ERR_NOT_FOUND);
+  }
+
+  // While in theory reply will always get initialized by KDDownload, things happen.
+  // Returning NWC24::WC24_ERR_BROKEN or anything that isn't OK will prompt the channel to fix the
+  // entry's data.
+  NWC24::ErrorCode reply = NWC24::WC24_ERR_BROKEN;
+
+  // Determine if we have subtasks to handle
+  if (Common::ExtractBit(flags, 2))
+  {
+    for (u8 subtask_id = 0; subtask_id < 32; subtask_id++)
+    {
+      // Check if we are done
+      if (!Common::ExtractBit(subtask_bitmask, subtask_id))
+      {
+        break;
+      }
+
+      reply = KDDownload(entry_index, subtask_id);
+      if (reply != NWC24::WC24_OK)
+      {
+        // An error has occurred, break out and return error.
+        break;
+      }
+    }
+  }
+  else
+  {
+    reply = KDDownload(entry_index, std::nullopt);
+  }
+
+  WriteReturnValue(reply, request.buffer_out);
+  return IPCReply(reply);
+}
+
 std::optional<IPCReply> NetKDRequestDevice::IOCtl(const IOCtlRequest& request)
 {
   enum : u32
@@ -288,6 +424,9 @@ std::optional<IPCReply> NetKDRequestDevice::IOCtl(const IOCtlRequest& request)
     INFO_LOG_FMT(IOS_WC24, "NET_KD_REQ: IOCTL_NWC24_SAVE_MAIL_NOW - NI");
     break;
 
+  case IOCTL_NWC24_DOWNLOAD_NOW_EX:
+    return LaunchAsyncTask(&NetKDRequestDevice::HandleNWC24DownloadNowEx, request);
+
   case IOCTL_NWC24_REQUEST_SHUTDOWN:
   {
     if (request.buffer_in == 0 || request.buffer_in % 4 != 0 || request.buffer_in_size < 8 ||

Source/Core/Core/IOS/Network/KD/NetKDRequest.h

@@ -3,13 +3,21 @@
 
 #pragma once
 
+#include <queue>
 #include <string>
 
+#include "Common/CommonPaths.h"
+#include "Common/CommonTypes.h"
+#include "Common/HttpRequest.h"
+#include "Common/WorkQueueThread.h"
 #include "Core/IOS/Device.h"
 #include "Core/IOS/Network/KD/NWC24Config.h"
+#include "Core/IOS/Network/KD/NWC24DL.h"
 
 namespace IOS::HLE
 {
+constexpr const char DL_CNT_PATH[] = "/" WII_WC24CONF_DIR "/dlcnt.bin";
+
 // KD is the IOS module responsible for implementing WiiConnect24 functionality.
 // It can perform HTTPS downloads, send and receive mail via SMTP, and execute a
 // JavaScript-like language while the Wii is in standby mode.
@@ -17,11 +25,39 @@ class NetKDRequestDevice : public Device
 {
 public:
   NetKDRequestDevice(Kernel& ios, const std::string& device_name);
+  IPCReply HandleNWC24DownloadNowEx(const IOCtlRequest& request);
+  NWC24::ErrorCode KDDownload(const u16 entry_index, const std::optional<u8> subtask_id);
   ~NetKDRequestDevice() override;
 
   std::optional<IPCReply> IOCtl(const IOCtlRequest& request) override;
+  void Update() override;
 
 private:
+  struct AsyncTask
+  {
+    IOS::HLE::Request request;
+    std::function<IPCReply()> handler;
+  };
+
+  struct AsyncReply
+  {
+    IOS::HLE::Request request;
+    s32 return_value;
+  };
+
+  template <typename Method, typename Request>
+  std::optional<IPCReply> LaunchAsyncTask(Method method, const Request& request)
+  {
+    m_work_queue.EmplaceItem(AsyncTask{request, std::bind(method, this, request)});
+    return std::nullopt;
+  }
+
   NWC24::NWC24Config config;
+  NWC24::NWC24Dl m_dl_list;
+  Common::WorkQueueThread<AsyncTask> m_work_queue;
+  std::mutex m_async_reply_lock;
+  std::queue<AsyncReply> m_async_replies;
+  // TODO: Maybe move away from Common::HttpRequest?
+  Common::HttpRequest m_http{std::chrono::minutes{1}};
 };
 }  // namespace IOS::HLE

Source/Core/Core/IOS/Network/KD/VFF/VFFUtil.cpp

@@ -0,0 +1,308 @@
+// Copyright 2022 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "Core/IOS/Network/KD/VFF/VFFUtil.h"
+
+#include <algorithm>
+#include <cmath>
+#include <vector>
+
+#include <fmt/format.h>
+
+// Does not compile if diskio.h is included first.
+// clang-format off
+#include "ff.h"
+#include "diskio.h"
+// clang-format on
+
+#include "Common/Align.h"
+#include "Common/FatFsUtil.h"
+#include "Common/Logging/Log.h"
+#include "Common/ScopeGuard.h"
+#include "Common/Swap.h"
+
+#include "Core/IOS/Uids.h"
+
+static DRESULT read_vff_header(IOS::HLE::FS::FileHandle* vff, FATFS* fs)
+{
+  struct IOS::HLE::NWC24::VFFHeader header;
+  if (!vff->Read(&header, 1))
+  {
+    ERROR_LOG_FMT(IOS_WC24, "Failed to read VFF header.");
+    return RES_ERROR;
+  }
+
+  u16 cluster_size = 0;
+  u16 cluster_count = 0;
+
+  switch (Common::swap16(header.endianness))
+  {
+  case IOS::HLE::NWC24::VF_BIG_ENDIAN:
+    cluster_size = Common::swap16(header.cluster_size) * 16;
+    cluster_count = Common::swap32(header.volume_size) / cluster_size;
+    break;
+  case IOS::HLE::NWC24::VF_LITTLE_ENDIAN:
+    // TODO: Actually implement.
+    // Another option is to just delete these VFFs and let the current channel create a Big Endian
+    // one.
+    return RES_ERROR;
+  }
+
+  if (cluster_count < 4085)
+  {
+    fs->fs_type = FS_FAT12;
+
+    u32 table_size = ((cluster_count + 1) / 2) * 3;
+    table_size = Common::AlignUp(table_size, cluster_size);
+
+    // Fsize is the full table size divided by 512 (Cluster size).
+    fs->fsize = table_size / 512;
+  }
+  else if (cluster_count < 65525)
+  {
+    fs->fs_type = FS_FAT16;
+
+    u32 table_size = cluster_count * 2;
+    table_size = Common::AlignUp(table_size, cluster_size);
+    fs->fsize = table_size / 512;
+  }
+  else
+  {
+    ERROR_LOG_FMT(IOS_WC24, "VFF not FAT12 or 16! Cluster size: {}", cluster_size);
+    return RES_ERROR;
+  }
+
+  fs->n_fats = 2;
+  fs->csize = 1;
+
+  // Root directory entry is 4096 bytes long, with each entry being 32 bytes. 4096 / 32 = 128
+  fs->n_rootdir = 128;
+
+  u32 sysect = 1 + (fs->fsize * 2) + fs->n_rootdir / (512 / 32);
+
+  // cluster_count is the total count whereas this is the actual amount of clusters we can use
+  u32 actual_cluster_count = cluster_count - sysect;
+
+  fs->n_fatent = actual_cluster_count + 2;
+  fs->volbase = 0;
+  fs->fatbase = 1;
+  fs->database = sysect;
+  // Root directory entry
+  fs->dirbase = fs->fatbase + fs->fsize * 2;
+
+  // Initialize cluster allocation information
+  fs->last_clst = fs->free_clst = 0xFFFFFFFF;
+  fs->fsi_flag = 0x80;
+
+  fs->id = 0;
+  fs->cdir = 0;
+
+  return RES_OK;
+}
+
+static FRESULT vff_mount(IOS::HLE::FS::FileHandle* vff, FATFS* fs)
+{
+  fs->fs_type = 0;  // Clear the filesystem object
+  fs->pdrv = 0;     // Volume hosting physical drive
+
+  DRESULT ret = read_vff_header(vff, fs);
+  if (ret != RES_OK)
+    return FR_DISK_ERR;
+
+  return FR_OK;
+}
+
+static DRESULT vff_read(IOS::HLE::FS::FileHandle* vff, BYTE pdrv, BYTE* buff, LBA_t sector,
+                        UINT count)
+{
+  // We cannot read or write data to the 0th sector in a VFF.
+  if (sector == 0)
+  {
+    ERROR_LOG_FMT(IOS_WC24, "Attempted to read the 0th sector in the VFF: Invalid VFF?");
+    return RES_ERROR;
+  }
+
+  const u64 offset = static_cast<u64>(sector) * IOS::HLE::NWC24::SECTOR_SIZE - 480;
+  if (!vff->Seek(offset, IOS::HLE::FS::SeekMode::Set))
+  {
+    ERROR_LOG_FMT(IOS_WC24, "VFF seek failed (offset={})", offset);
+    return RES_ERROR;
+  }
+
+  const size_t size = static_cast<size_t>(count) * IOS::HLE::NWC24::SECTOR_SIZE;
+  if (!vff->Read(buff, size))
+  {
+    ERROR_LOG_FMT(IOS_WC24, "VFF read failed (offset={}, size={})", offset, size);
+    return RES_ERROR;
+  }
+
+  return RES_OK;
+}
+
+static DRESULT vff_write(IOS::HLE::FS::FileHandle* vff, BYTE pdrv, const BYTE* buff, LBA_t sector,
+                         UINT count)
+{
+  if (sector == 0)
+  {
+    ERROR_LOG_FMT(IOS_WC24, "Attempted to write to the 0th sector in the VFF: Invalid VFF?");
+    return RES_ERROR;
+  }
+
+  const u64 offset = static_cast<u64>(sector) * IOS::HLE::NWC24::SECTOR_SIZE - 480;
+  if (!vff->Seek(offset, IOS::HLE::FS::SeekMode::Set))
+  {
+    ERROR_LOG_FMT(IOS_WC24, "VFF seek failed (offset={})", offset);
+    return RES_ERROR;
+  }
+
+  const size_t size = static_cast<size_t>(count) * IOS::HLE::NWC24::SECTOR_SIZE;
+  const auto res = vff->Write(buff, size);
+  if (!res)
+  {
+    ERROR_LOG_FMT(IOS_WC24, "VFF write failed (offset={}, size={})", offset, size);
+    return RES_ERROR;
+  }
+
+  return RES_OK;
+}
+
+static DRESULT vff_ioctl(IOS::HLE::FS::FileHandle* vff, BYTE pdrv, BYTE cmd, void* buff)
+{
+  switch (cmd)
+  {
+  case CTRL_SYNC:
+    return RES_OK;
+  case GET_SECTOR_COUNT:
+    *reinterpret_cast<LBA_t*>(buff) = vff->GetStatus()->size / IOS::HLE::NWC24::SECTOR_SIZE;
+    return RES_OK;
+  default:
+    WARN_LOG_FMT(IOS_WC24, "Unexpected FAT ioctl {}", cmd);
+    return RES_OK;
+  }
+}
+
+namespace IOS::HLE::NWC24
+{
+static ErrorCode WriteFile(const std::string& filename, const std::vector<u8>& tmp_buffer)
+{
+  FIL dst;
+  const auto open_error_code = f_open(&dst, filename.c_str(), FA_CREATE_ALWAYS | FA_WRITE);
+  if (open_error_code != FR_OK)
+  {
+    ERROR_LOG_FMT(IOS_WC24, "Failed to open file {} in VFF", filename);
+    return WC24_ERR_FILE_OPEN;
+  }
+
+  size_t size = tmp_buffer.size();
+  size_t offset = 0;
+  while (size > 0)
+  {
+    constexpr size_t MAX_CHUNK_SIZE = 32768;
+    u32 chunk_size = static_cast<u32>(std::min(size, MAX_CHUNK_SIZE));
+
+    u32 written_size;
+    const auto write_error_code =
+        f_write(&dst, tmp_buffer.data() + offset, chunk_size, &written_size);
+    if (write_error_code != FR_OK)
+    {
+      ERROR_LOG_FMT(IOS_WC24, "Failed to write file {} to VFF {}", filename, write_error_code);
+      return WC24_ERR_FILE_WRITE;
+    }
+
+    if (written_size != chunk_size)
+    {
+      ERROR_LOG_FMT(IOS_WC24, "Failed to write bytes of file {} to VFF ({} != {})", filename,
+                    written_size, chunk_size);
+      return WC24_ERR_FILE_WRITE;
+    }
+
+    size -= chunk_size;
+    offset += chunk_size;
+  }
+
+  const auto close_error_code = f_close(&dst);
+  if (close_error_code != FR_OK)
+  {
+    ERROR_LOG_FMT(IOS_WC24, "Failed to close file {} in VFF", filename);
+    return WC24_ERR_FILE_CLOSE;
+  }
+
+  return WC24_OK;
+}
+
+namespace
+{
+class VffFatFsCallbacks : public Common::FatFsCallbacks
+{
+public:
+  int DiskRead(u8 pdrv, u8* buff, u32 sector, unsigned int count) override
+  {
+    return vff_read(m_vff, pdrv, buff, sector, count);
+  }
+
+  int DiskWrite(u8 pdrv, const u8* buff, u32 sector, unsigned int count) override
+  {
+    return vff_write(m_vff, pdrv, buff, sector, count);
+  }
+
+  int DiskIOCtl(u8 pdrv, u8 cmd, void* buff) override { return vff_ioctl(m_vff, pdrv, cmd, buff); }
+
+  IOS::HLE::FS::FileHandle* m_vff;
+};
+}  // namespace
+
+ErrorCode OpenVFF(const std::string& path, const std::string& filename,
+                  const std::shared_ptr<FS::FileSystem>& fs, const std::vector<u8>& data)
+{
+  VffFatFsCallbacks callbacks;
+  ErrorCode return_value;
+  Common::RunInFatFsContext(callbacks, [&]() {
+    auto temp = fs->OpenFile(PID_KD, PID_KD, path, FS::Mode::ReadWrite);
+    if (!temp)
+    {
+      ERROR_LOG_FMT(IOS_WC24, "Failed to open VFF at: {}", path);
+      return_value = WC24_ERR_NOT_FOUND;
+      return;
+    }
+
+    callbacks.m_vff = &*temp;
+
+    Common::ScopeGuard vff_delete_guard{[&] { fs->Delete(PID_KD, PID_KD, path); }};
+
+    FATFS fatfs;
+    const FRESULT fatfs_mount_error_code = f_mount(&fatfs, "", 0);
+    if (fatfs_mount_error_code != FR_OK)
+    {
+      // The VFF is most likely broken.
+      ERROR_LOG_FMT(IOS_WC24, "Failed to mount VFF at: {}", path);
+      return_value = WC24_ERR_BROKEN;
+      return;
+    }
+
+    const FRESULT vff_mount_error_code = vff_mount(callbacks.m_vff, &fatfs);
+    if (vff_mount_error_code != FR_OK)
+    {
+      // The VFF is most likely broken.
+      ERROR_LOG_FMT(IOS_WC24, "Failed to mount VFF at: {}", path);
+      return_value = WC24_ERR_BROKEN;
+      return;
+    }
+
+    Common::ScopeGuard unmount_guard{[] { f_unmount(""); }};
+
+    const auto write_error_code = WriteFile(filename, data);
+    if (write_error_code != WC24_OK)
+    {
+      return_value = write_error_code;
+      return;
+    }
+
+    vff_delete_guard.Dismiss();
+
+    return_value = WC24_OK;
+    return;
+  });
+
+  return return_value;
+}
+}  // namespace IOS::HLE::NWC24

Source/Core/Core/IOS/Network/KD/VFF/VFFUtil.h

@@ -0,0 +1,43 @@
+// Copyright 2022 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "Common/CommonTypes.h"
+#include "Core/IOS/FS/FileSystem.h"
+#include "Core/IOS/Network/KD/NWC24Config.h"
+
+namespace IOS::HLE
+{
+namespace FS
+{
+class FileSystem;
+}
+namespace NWC24
+{
+constexpr u16 SECTOR_SIZE = 512;
+constexpr u16 VF_LITTLE_ENDIAN = 0xFFFE;
+constexpr u16 VF_BIG_ENDIAN = 0xFEFF;
+ErrorCode OpenVFF(const std::string& path, const std::string& filename,
+                  const std::shared_ptr<FS::FileSystem>& fs, const std::vector<u8>& data);
+
+#pragma pack(push, 1)
+struct VFFHeader final
+{
+  u8 magic[4];
+  u16 endianness;
+  u16 unknown_marker;
+  u32 volume_size;
+  u16 cluster_size;
+  u16 empty;
+  u16 unknown;
+  u8 padding[14];
+};
+static_assert(sizeof(VFFHeader) == 32);
+#pragma pack(pop)
+}  // namespace NWC24
+}  // namespace IOS::HLE

Source/Core/Core/IOS/Network/KD/WC24File.h

@@ -0,0 +1,31 @@
+// Copyright 2022 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include "Common/CommonTypes.h"
+
+namespace IOS::HLE::NWC24
+{
+#pragma pack(push, 1)
+struct WC24File final
+{
+  char magic[4];
+  u32 version;
+  u32 filler;
+  u8 crypt_type;
+  u8 padding[3];
+  u8 reserved[32];
+  u8 iv[16];
+  u8 rsa_signature[256];
+};
+
+struct WC24PubkMod final
+{
+  u8 rsa_public[256];
+  u8 rsa_reserved[256];
+  u8 aes_key[16];
+  u8 aes_reserved[16];
+};
+#pragma pack(pop)
+}  // namespace IOS::HLE::NWC24

Source/Core/DolphinLib.props

@@ -352,6 +352,9 @@
     <ClInclude Include="Core\IOS\Network\KD\NetKDRequest.h" />
     <ClInclude Include="Core\IOS\Network\KD\NetKDTime.h" />
     <ClInclude Include="Core\IOS\Network\KD\NWC24Config.h" />
+    <ClInclude Include="Core\IOS\Network\KD\NWC24DL.h" />
+    <ClInclude Include="Core\IOS\Network\KD\VFF\VFFUtil.h" />
+    <ClInclude Include="Core\IOS\Network\KD\WC24File.h" />
     <ClInclude Include="Core\IOS\Network\MACUtils.h" />
     <ClInclude Include="Core\IOS\Network\NCD\Manage.h" />
     <ClInclude Include="Core\IOS\Network\NCD\WiiNetConfig.h" />
@@ -976,6 +979,8 @@
     <ClCompile Include="Core\IOS\Network\KD\NetKDRequest.cpp" />
     <ClCompile Include="Core\IOS\Network\KD\NetKDTime.cpp" />
     <ClCompile Include="Core\IOS\Network\KD\NWC24Config.cpp" />
+    <ClCompile Include="Core\IOS\Network\KD\NWC24DL.cpp" />
+    <ClCompile Include="Core\IOS\Network\KD\VFF\VFFUtil.cpp" />
     <ClCompile Include="Core\IOS\Network\MACUtils.cpp" />
     <ClCompile Include="Core\IOS\Network\NCD\Manage.cpp" />
     <ClCompile Include="Core\IOS\Network\NCD\WiiNetConfig.cpp" />