/// <summary>
/// Load the ID3v2 frames to a binary stream
/// </summary>
/// <param name="stream">Binary stream holding the ID3 Tag</param>
/// <returns>Model keeping the ID3 Tag structure</returns>
public static TagModel Deserialize(Stream stream)
{
var frameModel = new TagModel();
frameModel.Header.Deserialize(stream); // load the ID3v2 header
if (frameModel.Header.Version != 3 & frameModel.Header.Version != 4)
throw new NotImplementedException("ID3v2 Version " + frameModel.Header.Version + " is not supported.");
uint id3TagSize = frameModel.Header.TagSize;
if (frameModel.Header.Unsync == true)
{
var memory = new MemoryStream();
id3TagSize -= Sync.Unsafe(stream, memory, id3TagSize);
stream = memory; // This is now the stream
if (id3TagSize <= 0)
throw new InvalidTagException("Data is missing after the header.");
}
uint rawSize;
// load the extended header
if (frameModel.Header.ExtendedHeader == true)
{
frameModel.ExtendedHeader.Deserialize(stream);
rawSize = id3TagSize - frameModel.ExtendedHeader.Size;
if (id3TagSize <= 0)
throw new InvalidTagException("Data is missing after the extended header.");
}
else
{
rawSize = id3TagSize;
}
// Read the frames
if (rawSize <= 0)
throw new InvalidTagException("No frames are present in the Tag, there must be at least one present.");
// Load the tag frames
uint index = 0;
var frameHelper = new FrameHelper(frameModel.Header);
// repeat while there is at least one complete frame available, 10 is the minimum size of a valid frame
// but what happens when there's only, say, 5 bytes of padding?
// we need to read a single byte to inspect for padding, then if not, read a whole tag.
while (index < rawSize)
{
byte[] frameId = new byte[4];
stream.Read(frameId, 0, 1);
if (frameId[0] == 0)
{
// We reached the padding area between the frames and the end of the tag,
// signified by a zero byte where the frame name should be.
// we could double check we actually know what's going on
// and check the padding goes exactly to the end of the id3 tag
// but in fact it doesn't give us any benefit.
//
// one of the following cases must apply:
//
// 1) if the id3 tag specifies more bytes than the frames use up,
// and that space is exactly filled with zeros to the first audio frame,
// it complies with the standard and everything is happy.
//
// 2) if the id3 tag specifies more bytes than the frames use up,
// and that space isn't completely filled with zeros,
// we assume the software that generated the tag
// forgot to zero-fill it properly.
//
// 3) if the zero padding extends past the start of the id3 tag,
// we assume the audio payload starts with skippable stuff too.
//
// 4) if the audio payload doesn't start with a valid mpeg audio frame header,
// (VBR headers have valid mpeg audio frame headers)
// we assume there's a tag in a format we don't recognise.
// It still has to comply with the mpeg sync rules,
// so we will have to use that to find the start of the audio.
//
// in all cases, we read the specified length of the id3 tag
// and let the higher-level processing inspect the audio payload
// to decide what is audio, what is extra padding,
// and what is unrecognised (non-id3) tags.
// how much does the tag size say should be left?
frameModel.Header.PaddingSize = rawSize - index;
//// advance the stream past any zero bytes,
//// and verify the real measured size against that specified in the tag
//uint observed = SeekEndOfPadding(src) + 1;
//if( frameModel.Header.PaddingSize != observed )
// throw new InvalidPaddingException(observed, frameModel.Header.PaddingSize);
// advance the stream to the specified end of the tag
// this skips any non-zero rubbish in the padding without looking at it.
stream.Seek(frameModel.Header.PaddingSize - 1, SeekOrigin.Current);
break;
}
if (index + 10 > rawSize)
{
// 10 is the minimum size of a valid frame;
// we read one already, if less than 9 chars left it's an error.
throw new InvalidTagException("Tag is corrupt, must be formed of complete frames.");
}
// read another 3 chars
stream.Read(frameId, 1, 3);
index += 4; // have read 4 bytes
//TODO: Validate key valid ranges
var reader = new BinaryReader(stream);
uint frameSize = Swap.UInt32(reader.ReadUInt32());
index += 4; // have read 4 bytes
// ID3v2.4 now has sync-safe sizes
if (frameModel.Header.Version == 4)
frameSize = Sync.Unsafe(frameSize);
// The size of the frame can't be larger than the available space
if (frameSize > rawSize - index)
throw new InvalidFrameException("A frame is corrupt, it can't be larger than the available space remaining.");
ushort flags = Swap.UInt16(reader.ReadUInt16());
index += 2; // read 2 bytes
byte[] frameData = new byte[frameSize];
reader.Read(frameData, 0, (int)frameSize);
index += frameSize; // read more bytes
frameModel.Add(frameHelper.Build(UTF8Encoding.UTF8.GetString(frameId, 0, 4), flags, frameData));
}
return frameModel;
}
/// <summary>
/// Save the ID3v2 frames to a binary stream
/// </summary>
/// <param name="frameModel">Model keeping the ID3 Tag structure</param>
/// <param name="stream">Stream keeping the ID3 Tag</param>
public static void Serialize(TagModel frameModel, Stream stream)
{
if (frameModel.Count <= 0)
throw new InvalidTagException("Can't serialize a ID3v2 tag without any frames, there must be at least one present.");
var memory = new MemoryStream();
var writer = new BinaryWriter(memory);
var frameHelper = new FrameHelper(frameModel.Header);
// Write the frames in binary format
foreach (FrameBase frame in frameModel)
{
//TODO: Do validations on tag name correctness
byte[] frameId = new byte[4];
UTF8Encoding.UTF8.GetBytes(frame.FrameId, 0, 4, frameId, 0);
writer.Write(frameId); // Write the 4 byte text tag
ushort flags;
byte[] buffer = frameHelper.Make(frame, out flags);
uint frameSize = (uint)buffer.Length;
if (frameModel.Header.Version == 4)
frameSize = Sync.Safe(frameSize);
writer.Write(Swap.UInt32(frameSize));
writer.Write(Swap.UInt16(flags));
writer.Write(buffer);
}
uint id3TagSize = (uint)memory.Position;
// Skip the header 10 bytes for now, we will come back and write the Header
// with the correct size once have the tag size + padding
stream.Seek(10, SeekOrigin.Begin);
// TODO: Add extended header handling
if (frameModel.Header.Unsync == true)
id3TagSize += Sync.Safe(memory, stream, id3TagSize);
else
memory.WriteTo(stream);
// update the TagSize stored in the tagModel
frameModel.Header.TagSize = id3TagSize;
// next write the padding of zeros, if any
if (frameModel.Header.Padding)
{
for (int i = 0; i < frameModel.Header.PaddingSize; i++)
stream.WriteByte(0);
}
// next write the footer, if any
if (frameModel.Header.Footer)
frameModel.Header.SerializeFooter(stream);
// Now seek back to the start and write the header
long position = stream.Position;
stream.Seek(0, SeekOrigin.Begin);
frameModel.Header.Serialize(stream);
// reset position to the end of the tag
stream.Position = position;
}
