WIA: Implement caching and partial decompression

2 files changed, 371 insertions, 268 deletions

diff --git a/Source/Core/DiscIO/WIABlob.cpp b/Source/Core/DiscIO/WIABlob.cpp
index d0f3eb490b..d58543cdb3 100644
--- a/Source/Core/DiscIO/WIABlob.cpp
+++ b/Source/Core/DiscIO/WIABlob.cpp
@@ -7,6 +7,7 @@
 #include <algorithm>
 #include <array>
 #include <cstring>
+#include <limits>
 #include <memory>
 #include <utility>
 
@@ -122,13 +123,12 @@ bool WIAFileReader::Initialize(const std::string& path)
 
   const u32 number_of_raw_data_entries = Common::swap32(m_header_2.number_of_raw_data_entries);
   m_raw_data_entries.resize(number_of_raw_data_entries);
-  if (!ReadCompressedData(number_of_raw_data_entries * sizeof(RawDataEntry),
-                          Common::swap64(m_header_2.raw_data_entries_offset),
-                          Common::swap32(m_header_2.raw_data_entries_size),
-                          reinterpret_cast<u8*>(m_raw_data_entries.data()), false))
-  {
+  Chunk& raw_data_entries =
+      ReadCompressedData(Common::swap64(m_header_2.raw_data_entries_offset),
+                         Common::swap32(m_header_2.raw_data_entries_size),
+                         number_of_raw_data_entries * sizeof(RawDataEntry), false);
+  if (!raw_data_entries.ReadAll(&m_raw_data_entries))
     return false;
-  }
 
   std::sort(m_raw_data_entries.begin(), m_raw_data_entries.end(),
             [](const RawDataEntry& a, const RawDataEntry& b) {
@@ -137,13 +137,11 @@ bool WIAFileReader::Initialize(const std::string& path)
 
   const u32 number_of_group_entries = Common::swap32(m_header_2.number_of_group_entries);
   m_group_entries.resize(number_of_group_entries);
-  if (!ReadCompressedData(number_of_group_entries * sizeof(GroupEntry),
-                          Common::swap64(m_header_2.group_entries_offset),
-                          Common::swap32(m_header_2.group_entries_size),
-                          reinterpret_cast<u8*>(m_group_entries.data()), false))
-  {
+  Chunk& group_entries = ReadCompressedData(Common::swap64(m_header_2.group_entries_offset),
+                                            Common::swap32(m_header_2.group_entries_size),
+                                            number_of_group_entries * sizeof(GroupEntry), false);
+  if (!group_entries.ReadAll(&m_group_entries))
     return false;
-  }
 
   return true;
 }
@@ -260,9 +258,11 @@ bool WIAFileReader::ReadFromGroups(u64* offset, u64* size, u8** out_ptr, u64 chu
     else
     {
       const u64 group_offset_in_file = static_cast<u64>(Common::swap32(group.data_offset)) << 2;
-      if (!ReadCompressedData(chunk_size, group_offset_in_file, group_data_size, offset_in_group,
-                              bytes_to_read, *out_ptr, exception_list))
+      Chunk& chunk =
+          ReadCompressedData(group_offset_in_file, group_data_size, chunk_size, exception_list);
+      if (!chunk.Read(offset_in_group, bytes_to_read, *out_ptr))
       {
+        m_cached_chunk_offset = std::numeric_limits<u64>::max();  // Invalidate the cache
         return false;
       }
     }
@@ -275,248 +275,193 @@ bool WIAFileReader::ReadFromGroups(u64* offset, u64* size, u8** out_ptr, u64 chu
   return true;
 }
 
-bool WIAFileReader::ReadCompressedData(u32 decompressed_data_size, u64 data_offset, u64 data_size,
-                                       u8* out_ptr, bool exception_list)
+WIAFileReader::Chunk& WIAFileReader::ReadCompressedData(u64 offset_in_file, u64 compressed_size,
+                                                        u64 decompressed_size, bool exception_list)
 {
+  if (offset_in_file == m_cached_chunk_offset)
+    return m_cached_chunk;
+
+  std::unique_ptr<Decompressor> decompressor;
   switch (m_compression_type)
   {
   case CompressionType::None:
-  {
-    return ReadCompressedData(decompressed_data_size, data_offset, data_size, 0,
-                              decompressed_data_size, out_ptr, exception_list);
-  }
-
+    decompressor = std::make_unique<NoneDecompressor>();
+    break;
   case CompressionType::Purge:
-  {
-    if (!m_file.Seek(data_offset, SEEK_SET))
-      return false;
-
-    if (exception_list)
-    {
-      const std::optional<u64> exception_size = ReadExceptionListFromFile();
-      if (!exception_size)
-        return false;
-
-      data_size -= *exception_size;
-    }
-
-    const u64 hash_offset = data_size - sizeof(SHA1);
-    u32 offset_in_data = 0;
-    u32 offset_in_decompressed_data = 0;
-
-    while (offset_in_data < hash_offset)
-    {
-      PurgeSegment purge_segment;
-      if (!m_file.ReadArray(&purge_segment, 1))
-        return false;
+    decompressor = std::make_unique<PurgeDecompressor>(decompressed_size);
+    break;
+  case CompressionType::Bzip2:
+    decompressor = std::make_unique<Bzip2Decompressor>();
+    break;
+  case CompressionType::LZMA:
+    decompressor = std::make_unique<LZMADecompressor>(false, m_header_2.compressor_data,
+                                                      m_header_2.compressor_data_size);
+    break;
+  case CompressionType::LZMA2:
+    decompressor = std::make_unique<LZMADecompressor>(true, m_header_2.compressor_data,
+                                                      m_header_2.compressor_data_size);
+    break;
+  }
 
-      const u32 segment_offset = Common::swap32(purge_segment.offset);
-      const u32 segment_size = Common::swap32(purge_segment.size);
+  const bool compressed_exception_list = m_compression_type > CompressionType::Purge;
 
-      if (segment_offset < offset_in_decompressed_data)
-        return false;
+  m_cached_chunk = Chunk(&m_file, offset_in_file, compressed_size, decompressed_size,
+                         exception_list, compressed_exception_list, std::move(decompressor));
+  m_cached_chunk_offset = offset_in_file;
+  return m_cached_chunk;
+}
 
-      const u32 blank_bytes = segment_offset - offset_in_decompressed_data;
-      std::memset(out_ptr, 0, blank_bytes);
-      out_ptr += blank_bytes;
+std::string WIAFileReader::VersionToString(u32 version)
+{
+  const u8 a = version >> 24;
+  const u8 b = (version >> 16) & 0xff;
+  const u8 c = (version >> 8) & 0xff;
+  const u8 d = version & 0xff;
 
-      if (segment_size != 0 && !m_file.ReadBytes(out_ptr, segment_size))
-        return false;
-      out_ptr += segment_size;
+  if (d == 0 || d == 0xff)
+    return StringFromFormat("%u.%02x.%02x", a, b, c);
+  else
+    return StringFromFormat("%u.%02x.%02x.beta%u", a, b, c, d);
+}
 
-      offset_in_data += sizeof(PurgeSegment) + segment_size;
-      offset_in_decompressed_data = segment_offset + segment_size;
-    }
+WIAFileReader::Decompressor::~Decompressor() = default;
 
-    if (offset_in_data != hash_offset || offset_in_decompressed_data > decompressed_data_size)
-      return false;
+bool WIAFileReader::NoneDecompressor::Decompress(const DecompressionBuffer& in,
+                                                 DecompressionBuffer* out, size_t* in_bytes_read)
+{
+  const size_t length =
+      std::min(in.bytes_written - *in_bytes_read, out->data.size() - out->bytes_written);
 
-    std::memset(out_ptr, 0, decompressed_data_size - offset_in_decompressed_data);
+  std::memcpy(out->data.data() + out->bytes_written, in.data.data() + *in_bytes_read, length);
 
-    SHA1 expected_hash;
-    if (!m_file.ReadArray(&expected_hash, 1))
-      return false;
+  *in_bytes_read += length;
+  out->bytes_written += length;
 
-    // TODO: Check hash
+  m_done = in.data.size() == *in_bytes_read;
+  return true;
+}
 
-    return true;
-  }
+WIAFileReader::PurgeDecompressor::PurgeDecompressor(u64 decompressed_size)
+    : m_decompressed_size(decompressed_size)
+{
+}
 
-  case CompressionType::Bzip2:
-  case CompressionType::LZMA:
-  case CompressionType::LZMA2:
+bool WIAFileReader::PurgeDecompressor::Decompress(const DecompressionBuffer& in,
+                                                  DecompressionBuffer* out, size_t* in_bytes_read)
+{
+  while (!m_done && in.bytes_written != *in_bytes_read &&
+         (m_segment_bytes_written < sizeof(m_segment) || out->data.size() != out->bytes_written))
   {
-    std::vector<u8> compressed_data(data_size);
-    if (!m_file.Seek(data_offset, SEEK_SET) || !m_file.ReadBytes(compressed_data.data(), data_size))
-      return false;
-
-    std::unique_ptr<Decompressor> decompressor;
-    switch (m_compression_type)
+    if (m_segment_bytes_written == 0 && *in_bytes_read == in.data.size() - sizeof(SHA1))
     {
-    case CompressionType::Bzip2:
-      decompressor = std::make_unique<Bzip2Decompressor>();
-      break;
-    case CompressionType::LZMA:
-      decompressor = std::make_unique<LZMADecompressor>(false, m_header_2.compressor_data,
-                                                        m_header_2.compressor_data_size);
-      break;
-    case CompressionType::LZMA2:
-      decompressor = std::make_unique<LZMADecompressor>(true, m_header_2.compressor_data,
-                                                        m_header_2.compressor_data_size);
-      break;
-    }
+      const size_t zeroes_to_write = std::min<size_t>(m_decompressed_size - m_out_bytes_written,
+                                                      out->data.size() - out->bytes_written);
 
-    if (!decompressor->Start(compressed_data.data(), compressed_data.size()))
-      return false;
+      std::memset(out->data.data() + out->bytes_written, 0, zeroes_to_write);
 
-    if (exception_list)
-    {
-      u16 exceptions;
-      if (decompressor->Read(reinterpret_cast<u8*>(&exceptions), sizeof(exceptions)) !=
-          sizeof(exceptions))
+      out->bytes_written += zeroes_to_write;
+      m_out_bytes_written += zeroes_to_write;
+
+      if (m_out_bytes_written == m_decompressed_size)
       {
-        return false;
-      }
+        *in_bytes_read += sizeof(SHA1);
+        m_done = true;
 
-      std::vector<HashExceptionEntry> exception_entries(Common::swap16(exceptions));
-      u8* exceptions_data = reinterpret_cast<u8*>(exception_entries.data());
-      const size_t exceptions_size = exception_entries.size() * sizeof(HashExceptionEntry);
-      if (decompressor->Read(exceptions_data, exceptions_size) != exceptions_size)
-        return false;
+        // TODO: Check hash
+      }
 
-      // TODO: Actually handle the exceptions
+      return true;
     }
 
-    if (decompressor->Read(out_ptr, decompressed_data_size) != decompressed_data_size)
-      return false;
+    if (m_segment_bytes_written < sizeof(m_segment))
+    {
+      const size_t bytes_to_copy =
+          std::min(in.bytes_written - *in_bytes_read, sizeof(m_segment) - m_segment_bytes_written);
 
-    if (!decompressor->DoneReading())
-      return false;
+      std::memcpy(reinterpret_cast<u8*>(&m_segment) + m_segment_bytes_written,
+                  in.data.data() + *in_bytes_read, bytes_to_copy);
 
-    return true;
-  }
-  }
+      *in_bytes_read += bytes_to_copy;
+      m_bytes_read += bytes_to_copy;
+      m_segment_bytes_written += bytes_to_copy;
+    }
 
-  return false;
-}
+    if (m_segment_bytes_written < sizeof(m_segment))
+      return true;
 
-bool WIAFileReader::ReadCompressedData(u32 decompressed_data_size, u64 data_offset, u64 data_size,
-                                       u64 offset_in_data, u64 size_in_data, u8* out_ptr,
-                                       bool exception_list)
-{
-  if (m_compression_type == CompressionType::None)
-  {
-    if (!m_file.Seek(data_offset, SEEK_SET))
-      return false;
+    const size_t offset = Common::swap32(m_segment.offset);
+    const size_t size = Common::swap32(m_segment.size);
 
-    if (exception_list)
+    if (m_out_bytes_written < offset)
     {
-      const std::optional<u64> exception_list_size = ReadExceptionListFromFile();
-      if (!exception_list_size)
-        return false;
+      const size_t zeroes_to_write =
+          std::min(offset - m_out_bytes_written, out->data.size() - out->bytes_written);
 
-      data_size -= *exception_list_size;
-    }
-
-    if (!m_file.Seek(offset_in_data, SEEK_CUR) || !m_file.ReadBytes(out_ptr, size_in_data))
-      return false;
+      std::memset(out->data.data() + out->bytes_written, 0, zeroes_to_write);
 
-    return true;
-  }
-  else
-  {
-    // TODO: Caching
-    std::vector<u8> buffer(decompressed_data_size);
-    if (!ReadCompressedData(decompressed_data_size, data_offset, data_size, buffer.data(),
-                            exception_list))
-    {
-      return false;
+      out->bytes_written += zeroes_to_write;
+      m_out_bytes_written += zeroes_to_write;
     }
-    std::memcpy(out_ptr, buffer.data() + offset_in_data, size_in_data);
-    return true;
-  }
-}
 
-std::optional<u64> WIAFileReader::ReadExceptionListFromFile()
-{
-  u16 exceptions;
-  if (!m_file.ReadArray(&exceptions, 1))
-    return std::nullopt;
-
-  const u64 exception_list_size = Common::AlignUp(
-      sizeof(exceptions) + Common::swap16(exceptions) * sizeof(HashExceptionEntry), 4);
-
-  if (!m_file.Seek(exception_list_size - sizeof(exceptions), SEEK_CUR))
-    return std::nullopt;
+    if (m_out_bytes_written >= offset && m_out_bytes_written < offset + size)
+    {
+      const size_t bytes_to_copy = std::min(
+          std::min(offset + size - m_out_bytes_written, out->data.size() - out->bytes_written),
+          in.bytes_written - *in_bytes_read);
 
-  // TODO: Actually handle the exceptions
+      std::memcpy(out->data.data() + out->bytes_written, in.data.data() + *in_bytes_read,
+                  bytes_to_copy);
 
-  return exception_list_size;
-}
+      *in_bytes_read += bytes_to_copy;
+      m_bytes_read += bytes_to_copy;
+      out->bytes_written += bytes_to_copy;
+      m_out_bytes_written += bytes_to_copy;
+    }
 
-std::string WIAFileReader::VersionToString(u32 version)
-{
-  const u8 a = version >> 24;
-  const u8 b = (version >> 16) & 0xff;
-  const u8 c = (version >> 8) & 0xff;
-  const u8 d = version & 0xff;
+    if (m_out_bytes_written >= offset + size)
+      m_segment_bytes_written = 0;
+  }
 
-  if (d == 0 || d == 0xff)
-    return StringFromFormat("%u.%02x.%02x", a, b, c);
-  else
-    return StringFromFormat("%u.%02x.%02x.beta%u", a, b, c, d);
+  return true;
 }
 
-WIAFileReader::Decompressor::~Decompressor() = default;
-
 WIAFileReader::Bzip2Decompressor::~Bzip2Decompressor()
 {
-  End();
+  if (m_started)
+    BZ2_bzDecompressEnd(&m_stream);
 }
 
-bool WIAFileReader::Bzip2Decompressor::Start(const u8* in_ptr, u64 size)
+bool WIAFileReader::Bzip2Decompressor::Decompress(const DecompressionBuffer& in,
+                                                  DecompressionBuffer* out, size_t* in_bytes_read)
 {
-  if (m_started)
-    return false;
-
-  m_stream.bzalloc = nullptr;
-  m_stream.bzfree = nullptr;
-  m_stream.opaque = nullptr;
+  if (!m_started)
+  {
+    if (BZ2_bzDecompressInit(&m_stream, 0, 0) != BZ_OK)
+      return false;
 
-  m_started = BZ2_bzDecompressInit(&m_stream, 0, 0) == BZ_OK;
+    m_started = true;
+  }
 
-  m_stream.next_in = reinterpret_cast<char*>(const_cast<u8*>(in_ptr));
-  m_stream.avail_in = size;
+  constexpr auto clamped_cast = [](size_t x) {
+    return static_cast<unsigned int>(
+        std::min<size_t>(std::numeric_limits<unsigned int>().max(), x));
+  };
 
-  return m_started;
-}
-
-u64 WIAFileReader::Bzip2Decompressor::Read(u8* out_ptr, u64 size)
-{
-  if (!m_started || m_error_occurred || m_stream.avail_in == 0)
-    return 0;
+  char* const in_ptr = reinterpret_cast<char*>(const_cast<u8*>(in.data.data() + *in_bytes_read));
+  m_stream.next_in = in_ptr;
+  m_stream.avail_in = clamped_cast(in.bytes_written - *in_bytes_read);
 
-  m_stream.next_out = reinterpret_cast<char*>(out_ptr);
-  m_stream.avail_out = size;
+  char* const out_ptr = reinterpret_cast<char*>(out->data.data() + out->bytes_written);
+  m_stream.next_out = out_ptr;
+  m_stream.avail_out = clamped_cast(out->data.size() - out->bytes_written);
 
   const int result = BZ2_bzDecompress(&m_stream);
-  m_error_occurred = result != BZ_OK && result != BZ_STREAM_END;
-
-  return m_error_occurred ? 0 : m_stream.next_out - reinterpret_cast<char*>(out_ptr);
-}
 
-bool WIAFileReader::Bzip2Decompressor::DoneReading() const
-{
-  return m_started && !m_error_occurred && m_stream.avail_in == 0;
-}
+  *in_bytes_read += m_stream.next_in - in_ptr;
+  out->bytes_written += m_stream.next_out - out_ptr;
 
-void WIAFileReader::Bzip2Decompressor::End()
-{
-  if (m_started && !m_ended)
-  {
-    BZ2_bzDecompressEnd(&m_stream);
-    m_ended = true;
-  }
+  m_done = result == BZ_STREAM_END;
+  return result == BZ_OK || result == BZ_STREAM_END;
 }
 
 WIAFileReader::LZMADecompressor::LZMADecompressor(bool lzma2, const u8* filter_options,
@@ -564,48 +509,162 @@ WIAFileReader::LZMADecompressor::LZMADecompressor(bool lzma2, const u8* filter_o
 
 WIAFileReader::LZMADecompressor::~LZMADecompressor()
 {
-  End();
+  if (m_started)
+    lzma_end(&m_stream);
 }
 
-bool WIAFileReader::LZMADecompressor::Start(const u8* in_ptr, u64 size)
+bool WIAFileReader::LZMADecompressor::Decompress(const DecompressionBuffer& in,
+                                                 DecompressionBuffer* out, size_t* in_bytes_read)
 {
-  if (m_started || m_error_occurred)
-    return false;
+  if (!m_started)
+  {
+    if (m_error_occurred || lzma_raw_decoder(&m_stream, m_filters) != LZMA_OK)
+      return false;
 
-  m_started = lzma_raw_decoder(&m_stream, m_filters) == LZMA_OK;
+    m_started = true;
+  }
 
+  const u8* const in_ptr = in.data.data() + *in_bytes_read;
   m_stream.next_in = in_ptr;
-  m_stream.avail_in = size;
-
-  return m_started;
-}
-
-u64 WIAFileReader::LZMADecompressor::Read(u8* out_ptr, u64 size)
-{
-  if (!m_started || m_error_occurred || m_stream.avail_in == 0)
-    return 0;
+  m_stream.avail_in = in.bytes_written - *in_bytes_read;
 
+  u8* const out_ptr = out->data.data() + out->bytes_written;
   m_stream.next_out = out_ptr;
-  m_stream.avail_out = size;
+  m_stream.avail_out = out->data.size() - out->bytes_written;
 
   const lzma_ret result = lzma_code(&m_stream, LZMA_RUN);
-  m_error_occurred = result != LZMA_OK && result != LZMA_STREAM_END;
 
-  return m_error_occurred ? 0 : m_stream.next_out - out_ptr;
+  *in_bytes_read += m_stream.next_in - in_ptr;
+  out->bytes_written += m_stream.next_out - out_ptr;
+
+  m_done = result == LZMA_STREAM_END;
+  return result == LZMA_OK || result == LZMA_STREAM_END;
 }
 
-bool WIAFileReader::LZMADecompressor::DoneReading() const
+WIAFileReader::Chunk::Chunk() = default;
+
+WIAFileReader::Chunk::Chunk(File::IOFile* file, u64 offset_in_file, u64 compressed_size,
+                            u64 decompressed_size, bool exception_list,
+                            bool compressed_exception_list,
+                            std::unique_ptr<Decompressor> decompressor)
+    : m_file(file), m_offset_in_file(offset_in_file), m_exception_list(exception_list),
+      m_compressed_exception_list(compressed_exception_list),
+      m_decompressor(std::move(decompressor))
 {
-  return m_started && !m_error_occurred && m_stream.avail_in == 0;
+  m_in.data.resize(compressed_size);
+  m_out.data.resize(decompressed_size);
 }
 
-void WIAFileReader::LZMADecompressor::End()
+bool WIAFileReader::Chunk::Read(u64 offset, u64 size, u8* out_ptr)
 {
-  if (m_started && !m_ended)
+  if (offset + size > m_out.data.size() || !m_decompressor || !m_file)
+    return false;
+
+  if (m_exception_list && !m_compressed_exception_list)
   {
-    lzma_end(&m_stream);
-    m_ended = true;
+    u16 exceptions;
+    if (!m_file->Seek(m_offset_in_file, SEEK_SET) || !m_file->ReadArray(&exceptions, 1))
+      return false;
+
+    m_exceptions.data.resize(Common::swap16(exceptions) * sizeof(HashExceptionEntry));
+    if (!m_file->ReadBytes(m_exceptions.data.data(), m_exceptions.data.size()))
+      return false;
+    m_exceptions.bytes_written = m_exceptions.data.size();
+
+    m_in.bytes_written = Common::AlignUp(sizeof(exceptions) + m_exceptions.data.size(), 4);
+    m_in_bytes_read = m_in.bytes_written;
+    m_exception_list = false;
+
+    // TODO: Actually handle the exceptions
   }
+
+  while (offset + size > m_out.bytes_written)
+  {
+    u64 bytes_to_read;
+    if (offset + size == m_out.data.size())
+    {
+      // Read all the remaining data.
+      bytes_to_read = m_in.data.size() - m_in.bytes_written;
+    }
+    else
+    {
+      // Pick a suitable amount of compressed data to read. The std::min line has to
+      // be as it is, but the rest is a bit arbitrary and can be changed if desired.
+
+      // The compressed data is probably not much bigger than the decompressed data.
+      // Add a few bytes for possible compression overhead and for the exception list.
+      bytes_to_read = offset + size - m_out.bytes_written + 0x100;
+
+      // Align the access in an attempt to gain speed. But we don't actually know the
+      // block size of the underlying storage device, so we just use the Wii block size.
+      bytes_to_read =
+          Common::AlignUp(bytes_to_read + m_offset_in_file, VolumeWii::BLOCK_TOTAL_SIZE) -
+          m_offset_in_file;
+
+      // Ensure we don't read too much.
+      bytes_to_read = std::min<u64>(m_in.data.size() - m_in.bytes_written, bytes_to_read);
+    }
+
+    if (bytes_to_read == 0)
+    {
+      // Compressed size is larger than expected or decompressed size is smaller than expected
+      return false;
+    }
+
+    if (!m_file->Seek(m_offset_in_file, SEEK_SET))
+      return false;
+    if (!m_file->ReadBytes(m_in.data.data() + m_in.bytes_written, bytes_to_read))
+      return false;
+
+    m_offset_in_file += bytes_to_read;
+    m_in.bytes_written += bytes_to_read;
+
+    if (m_exception_list)
+    {
+      if (m_exceptions.data.empty())
+        m_exceptions.data.resize(sizeof(u16));
+
+      if (m_exceptions.data.size() == sizeof(u16))
+      {
+        if (!m_decompressor->Decompress(m_in, &m_exceptions, &m_in_bytes_read))
+          return false;
+
+        if (m_exceptions.bytes_written == m_exceptions.data.size())
+        {
+          u16 exceptions;
+          std::memcpy(&exceptions, m_exceptions.data.data(), sizeof(exceptions));
+          m_exceptions.data.resize(Common::swap16(exceptions) * sizeof(HashExceptionEntry));
+          m_exceptions.bytes_written = 0;
+        }
+      }
+
+      if (m_exceptions.data.size() != sizeof(u16))
+      {
+        if (!m_decompressor->Decompress(m_in, &m_exceptions, &m_in_bytes_read))
+          return false;
+
+        if (m_exceptions.bytes_written == m_exceptions.data.size())
+          m_exception_list = false;
+
+        // TODO: Actually handle the exceptions
+      }
+    }
+
+    if (!m_exception_list)
+    {
+      if (!m_decompressor->Decompress(m_in, &m_out, &m_in_bytes_read))
+        return false;
+
+      if (m_out.bytes_written == m_out.data.size() && !m_decompressor->Done())
+        return false;  // Decompressed size is larger than expected
+
+      if (m_decompressor->Done() && m_in_bytes_read != m_in.data.size())
+        return false;  // Compressed size is smaller than expected
+    }
+  }
+
+  std::memcpy(out_ptr, m_out.data.data() + offset, size);
+  return true;
 }
 
 }  // namespace DiscIO
diff --git a/Source/Core/DiscIO/WIABlob.h b/Source/Core/DiscIO/WIABlob.h
index e7198e2467..205c48e127 100644
--- a/Source/Core/DiscIO/WIABlob.h
+++ b/Source/Core/DiscIO/WIABlob.h
@@ -5,6 +5,7 @@
 #pragma once
 
 #include <array>
+#include <limits>
 #include <memory>
 #include <utility>
 
@@ -41,25 +42,18 @@ public:
   bool ReadWiiDecrypted(u64 offset, u64 size, u8* out_ptr, u64 partition_data_offset) override;
 
 private:
-  explicit WIAFileReader(File::IOFile file, const std::string& path);
-  bool Initialize(const std::string& path);
-
-  bool ReadFromGroups(u64* offset, u64* size, u8** out_ptr, u64 chunk_size, u32 sector_size,
-                      u64 data_offset, u64 data_size, u32 group_index, u32 number_of_groups,
-                      bool exception_list);
-  bool ReadCompressedData(u32 decompressed_data_size, u64 data_offset, u64 data_size, u8* out_ptr,
-                          bool exception_list);
-  bool ReadCompressedData(u32 decompressed_data_size, u64 data_offset, u64 data_size,
-                          u64 offset_in_data, u64 size_in_data, u8* out_ptr, bool exception_list);
-
-  // Returns the number of bytes read
-  std::optional<u64> ReadExceptionListFromFile();
-
-  static std::string VersionToString(u32 version);
-
   using SHA1 = std::array<u8, 20>;
   using WiiKey = std::array<u8, 16>;
 
+  enum class CompressionType : u32
+  {
+    None = 0,
+    Purge = 1,
+    Bzip2 = 2,
+    LZMA = 3,
+    LZMA2 = 4,
+  };
+
 #pragma pack(push, 1)
   struct WIAHeader1
   {
@@ -148,13 +142,10 @@ private:
   static_assert(sizeof(PurgeSegment) == 0x08, "Wrong size for WIA purge segment");
 #pragma pack(pop)
 
-  enum class CompressionType : u32
+  struct DecompressionBuffer
   {
-    None = 0,
-    Purge = 1,
-    Bzip2 = 2,
-    LZMA = 3,
-    LZMA2 = 4,
+    std::vector<u8> data;
+    size_t bytes_written = 0;
   };
 
   class Decompressor
@@ -162,18 +153,36 @@ private:
   public:
     virtual ~Decompressor();
 
-    // Specifies the compressed data to read. The data must still be in memory when calling Read.
-    virtual bool Start(const u8* in_ptr, u64 size) = 0;
+    virtual bool Decompress(const DecompressionBuffer& in, DecompressionBuffer* out,
+                            size_t* in_bytes_read) = 0;
+    virtual bool Done() const { return m_done; };
+
+  protected:
+    bool m_done = false;
+  };
 
-    // Reads the specified number of bytes into out_ptr (or less, if there aren't that many bytes
-    // to output). Returns the number of bytes read. Start must be called before this.
-    virtual u64 Read(u8* out_ptr, u64 size) = 0;
+  class NoneDecompressor final : public Decompressor
+  {
+  public:
+    bool Decompress(const DecompressionBuffer& in, DecompressionBuffer* out,
+                    size_t* in_bytes_read) override;
+  };
 
-    // Returns whether every byte of the input data has been read.
-    virtual bool DoneReading() const = 0;
+  // This class assumes that more bytes won't be added to in once in.bytes_written == in.data.size()
+  class PurgeDecompressor final : public Decompressor
+  {
+  public:
+    PurgeDecompressor(u64 decompressed_size);
+    bool Decompress(const DecompressionBuffer& in, DecompressionBuffer* out,
+                    size_t* in_bytes_read) override;
 
-    // Will be called automatically upon destruction, but can be called earlier if desired.
-    virtual void End() = 0;
+  private:
+    PurgeSegment m_segment = {};
+    size_t m_bytes_read = 0;
+    size_t m_segment_bytes_written = 0;
+    size_t m_out_bytes_written = 0;
+
+    const u64 m_decompressed_size;
   };
 
   class Bzip2Decompressor final : public Decompressor
@@ -181,16 +190,12 @@ private:
   public:
     ~Bzip2Decompressor();
 
-    bool Start(const u8* in_ptr, u64 size) override;
-    u64 Read(u8* out_ptr, u64 size) override;
-    bool DoneReading() const override;
-    void End() override;
+    bool Decompress(const DecompressionBuffer& in, DecompressionBuffer* out,
+                    size_t* in_bytes_read) override;
 
   private:
-    bz_stream m_stream;
+    bz_stream m_stream = {};
     bool m_started = false;
-    bool m_ended = false;
-    bool m_error_occurred = false;
   };
 
   class LZMADecompressor final : public Decompressor
@@ -199,24 +204,63 @@ private:
     LZMADecompressor(bool lzma2, const u8* filter_options, size_t filter_options_size);
     ~LZMADecompressor();
 
-    bool Start(const u8* in_ptr, u64 size) override;
-    u64 Read(u8* out_ptr, u64 size) override;
-    bool DoneReading() const override;
-    void End() override;
+    bool Decompress(const DecompressionBuffer& in, DecompressionBuffer* out,
+                    size_t* in_bytes_read) override;
 
   private:
     lzma_stream m_stream = LZMA_STREAM_INIT;
     lzma_options_lzma m_options = {};
     lzma_filter m_filters[2];
     bool m_started = false;
-    bool m_ended = false;
     bool m_error_occurred = false;
   };
 
+  class Chunk
+  {
+  public:
+    Chunk();
+    Chunk(File::IOFile* file, u64 offset_in_file, u64 compressed_size, u64 decompressed_size,
+          bool exception_list, bool compressed_exception_list,
+          std::unique_ptr<Decompressor> decompressor);
+
+    bool Read(u64 offset, u64 size, u8* out_ptr);
+
+    template <typename T>
+    bool ReadAll(std::vector<T>* vector)
+    {
+      return Read(0, vector->size() * sizeof(T), reinterpret_cast<u8*>(vector->data()));
+    }
+
+  private:
+    DecompressionBuffer m_in;
+    DecompressionBuffer m_out;
+    DecompressionBuffer m_exceptions;
+    size_t m_in_bytes_read = 0;
+
+    std::unique_ptr<Decompressor> m_decompressor = nullptr;
+    File::IOFile* m_file = nullptr;
+    u64 m_offset_in_file = 0;
+    bool m_exception_list = false;
+    bool m_compressed_exception_list = false;
+  };
+
+  explicit WIAFileReader(File::IOFile file, const std::string& path);
+  bool Initialize(const std::string& path);
+
+  bool ReadFromGroups(u64* offset, u64* size, u8** out_ptr, u64 chunk_size, u32 sector_size,
+                      u64 data_offset, u64 data_size, u32 group_index, u32 number_of_groups,
+                      bool exception_list);
+  Chunk& ReadCompressedData(u64 offset_in_file, u64 compressed_size, u64 decompressed_size,
+                            bool exception_list);
+
+  static std::string VersionToString(u32 version);
+
   bool m_valid;
   CompressionType m_compression_type;
 
   File::IOFile m_file;
+  Chunk m_cached_chunk;
+  u64 m_cached_chunk_offset = std::numeric_limits<u64>::max();
 
   WIAHeader1 m_header_1;
   WIAHeader2 m_header_2;