Only open file once when detecting blob type

Source/Core/DiscIO/Blob.cpp

@@ -177,23 +177,31 @@ std::unique_ptr<IBlobReader> CreateBlobReader(const std::string& filename)
   if (cdio_is_cdrom(filename))
     return DriveReader::Create(filename);
 
-  if (!File::Exists(filename))
+  File::IOFile file(filename, "rb");
+  u32 magic;
+  if (!file.ReadArray(&magic, 1))
     return nullptr;
 
-  if (IsWbfsBlob(filename))
+  // Conveniently, every supported file format (except for plain disc images) starts
-    return WbfsFileReader::Create(filename);
+  // with a 4-byte magic number that identifies the format, so we just need a simple
+  // switch statement to create the right blob type. If the magic number doesn't
+  // match any known magic number, we assume it's a plain disc image. If that
+  // assumption is wrong, the volume code that runs later will notice the error
+  // because the blob won't provide valid data when reading the GC/Wii disc header.
 
-  if (IsGCZBlob(filename))
+  switch (magic)
-    return CompressedBlobReader::Create(filename);
+  {
-
+  case CISO_MAGIC:
-  if (IsCISOBlob(filename))
     return CISOFileReader::Create(filename);
-
+  case GCZ_MAGIC:
-  if (IsTGCBlob(filename))
+    return CompressedBlobReader::Create(filename);
+  case TGC_MAGIC:
     return TGCFileReader::Create(filename);
-
+  case WBFS_MAGIC:
-  // Still here? Assume plain file - since we know it exists due to the File::Exists check above.
+    return WbfsFileReader::Create(filename);
-  return PlainFileReader::Create(filename);
+  default:
+    return PlainFileReader::Create(filename);
+  }
 }
 
 }  // namespace

Source/Core/DiscIO/CISOBlob.cpp

@@ -12,8 +12,6 @@
 
 namespace DiscIO
 {
-static const char CISO_MAGIC[] = "CISO";
-
 CISOFileReader::CISOFileReader(std::FILE* file) : m_file(file)
 {
   m_size = m_file.GetSize();
@@ -30,11 +28,10 @@ CISOFileReader::CISOFileReader(std::FILE* file) : m_file(file)
 
 std::unique_ptr<CISOFileReader> CISOFileReader::Create(const std::string& filename)
 {
-  if (IsCISOBlob(filename))
+  File::IOFile f(filename, "rb");
-  {
+  CISOHeader header;
-    File::IOFile f(filename, "rb");
+  if (f.ReadArray(&header, 1) && header.magic == CISO_MAGIC)
     return std::unique_ptr<CISOFileReader>(new CISOFileReader(f.ReleaseHandle()));
-  }
 
   return nullptr;
 }
@@ -81,13 +78,4 @@ bool CISOFileReader::Read(u64 offset, u64 nbytes, u8* out_ptr)
   return true;
 }
 
-bool IsCISOBlob(const std::string& filename)
-{
-  File::IOFile f(filename, "rb");
-
-  CISOHeader header;
-  return (f.ReadArray(&header, 1) &&
-          std::equal(header.magic, header.magic + sizeof(header.magic), CISO_MAGIC));
-}
-
 }  // namespace

Source/Core/DiscIO/CISOBlob.h

@@ -14,7 +14,7 @@
 
 namespace DiscIO
 {
-bool IsCISOBlob(const std::string& filename);
+static constexpr u32 CISO_MAGIC = 0x4F534943;  // "CISO" (byteswapped to little endian)
 
 static const u32 CISO_HEADER_SIZE = 0x8000;
 static const u32 CISO_MAP_SIZE = CISO_HEADER_SIZE - sizeof(u32) - sizeof(char) * 4;
@@ -22,7 +22,7 @@ static const u32 CISO_MAP_SIZE = CISO_HEADER_SIZE - sizeof(u32) - sizeof(char) *
 struct CISOHeader
 {
   // "CISO"
-  char magic[4];
+  u32 magic;
 
   // little endian
   u32 block_size;

Source/Core/DiscIO/CompressedBlob.cpp

@@ -28,6 +28,8 @@
 
 namespace DiscIO
 {
+bool IsGCZBlob(const std::string& filename);
+
 CompressedBlobReader::CompressedBlobReader(const std::string& filename) : m_file_name(filename)
 {
   m_file.Open(filename, "rb");
@@ -192,7 +194,7 @@ bool CompressFileToBlob(const std::string& infile, const std::string& outfile, u
   callback(GetStringT("Files opened, ready to compress."), 0, arg);
 
   CompressedBlobHeader header;
-  header.magic_cookie = kBlobCookie;
+  header.magic_cookie = GCZ_MAGIC;
   header.sub_type = sub_type;
   header.block_size = block_size;
   header.data_size = File::GetSize(infile);
@@ -401,7 +403,7 @@ bool IsGCZBlob(const std::string& filename)
   File::IOFile f(filename, "rb");
 
   CompressedBlobHeader header;
-  return f.ReadArray(&header, 1) && (header.magic_cookie == kBlobCookie);
+  return f.ReadArray(&header, 1) && (header.magic_cookie == GCZ_MAGIC);
 }
 
 }  // namespace

Source/Core/DiscIO/CompressedBlob.h

@@ -23,9 +23,7 @@
 
 namespace DiscIO
 {
-bool IsGCZBlob(const std::string& filename);
+static constexpr u32 GCZ_MAGIC = 0xB10BC001;
-
-const u32 kBlobCookie = 0xB10BC001;
 
 // GCZ file structure:
 // BlobHeader

Source/Core/DiscIO/TGCBlob.cpp

@@ -56,21 +56,12 @@ void Replace32(u64 offset, u64 nbytes, u8* out_ptr, u64 replace_offset, u32 repl
 
 namespace DiscIO
 {
-bool IsTGCBlob(const std::string& path)
-{
-  File::IOFile file(path, "rb");
-
-  TGCHeader header;
-  return (file.ReadArray(&header, 1) && header.magic == Common::swap32(0xAE0F38A2));
-}
-
 std::unique_ptr<TGCFileReader> TGCFileReader::Create(const std::string& path)
 {
-  if (IsTGCBlob(path))
+  File::IOFile file(path, "rb");
-  {
+  TGCHeader header;
-    File::IOFile file(path, "rb");
+  if (file.ReadArray(&header, 1) && header.magic == TGC_MAGIC)
     return std::unique_ptr<TGCFileReader>(new TGCFileReader(std::move(file)));
-  }
 
   return nullptr;
 }

Source/Core/DiscIO/TGCBlob.h

@@ -14,7 +14,7 @@
 
 namespace DiscIO
 {
-bool IsTGCBlob(const std::string& path);
+static constexpr u32 TGC_MAGIC = 0xA2380FAE;
 
 struct TGCHeader
 {

Source/Core/DiscIO/WbfsBlob.cpp

@@ -83,8 +83,10 @@ bool WbfsFileReader::ReadHeader()
 {
   // Read hd size info
   m_files[0]->file.ReadBytes(&m_header, sizeof(WbfsHeader));
-  m_header.hd_sector_count = Common::swap32(m_header.hd_sector_count);
+  if (m_header.magic != WBFS_MAGIC)
+    return false;
 
+  m_header.hd_sector_count = Common::swap32(m_header.hd_sector_count);
   m_hd_sector_size = 1ull << m_header.hd_sector_shift;
 
   if (m_size != (m_header.hd_sector_count * m_hd_sector_size))
@@ -172,14 +174,4 @@ std::unique_ptr<WbfsFileReader> WbfsFileReader::Create(const std::string& filena
   return reader;
 }
 
-bool IsWbfsBlob(const std::string& filename)
-{
-  File::IOFile f(filename, "rb");
-
-  u8 magic[4] = {0, 0, 0, 0};
-  f.ReadBytes(&magic, 4);
-
-  return (magic[0] == 'W') && (magic[1] == 'B') && (magic[2] == 'F') && (magic[3] == 'S');
-}
-
 }  // namespace

Source/Core/DiscIO/WbfsBlob.h

@@ -14,6 +14,8 @@
 
 namespace DiscIO
 {
+static constexpr u32 WBFS_MAGIC = 0x53464257;  // "WBFS" (byteswapped to little endian)
+
 class WbfsFileReader : public IBlobReader
 {
 public:
@@ -58,7 +60,7 @@ private:
 #pragma pack(1)
   struct WbfsHeader
   {
-    char magic[4];
+    u32 magic;
     u32 hd_sector_count;
     u8 hd_sector_shift;
     u8 wbfs_sector_shift;
@@ -73,6 +75,4 @@ private:
   bool m_good;
 };
 
-bool IsWbfsBlob(const std::string& filename);
-
 }  // namespace