// Event called when the Id3v2 tag has read a frame.
// This event can be used to modify a read frame, as we do here, to further parse known frames.
private static void Id3v2FrameParsed(object sender, Id3v2FrameParsedEventArgs e)
{
// See if the frame is a comment frame.
if (!(e.Frame is Id3v2CommentFrame))
return;
// Safe-cast the frame to a comment frame.
Id3v2CommentFrame frame = e.Frame as Id3v2CommentFrame;
// See if the frame is an iTunes normalization frame.
if (!String.Equals(frame.ShortContentDescription, "iTunNORM", StringComparison.OrdinalIgnoreCase))
return;
byte[] frameData = e.Frame.ToByteArray();
// Parse the frame as an iTunes normalization frame.
Id3v2iTunesNormalizationFrame normalizationFrame = Id3v2Frame.ReadFromStream<Id3v2iTunesNormalizationFrame>(
e.Frame.Version,
new MemoryStream(frameData),
frameData.Length);
// Set the new normalization frame as the new frame; this will replace the comment frame.
e.Frame = normalizationFrame;
}
/// <summary>
/// Raises the <see cref="FrameParsed"/> event.
/// </summary>
/// <param name="e">The <see cref="AudioVideoLib.Tags.Id3v2FrameParsedEventArgs"/> instance containing the event data.</param>
private void OnFrameParsed(Id3v2FrameParsedEventArgs e)
{
EventHandler<Id3v2FrameParsedEventArgs> eventHandlers = FrameParsed;
if (eventHandlers != null)
eventHandlers(this, e);
}
////------------------------------------------------------------------------------------------------------------------------------
/// <inheritdoc/>
public IAudioTagOffset ReadFromStream(Stream stream, TagOrigin tagOrigin)
{
if (stream == null)
throw new ArgumentNullException("stream");
if (!stream.CanRead)
throw new InvalidOperationException("stream can not be read");
if (!stream.CanSeek)
throw new InvalidOperationException("stream can not be seeked");
StreamBuffer sb = stream as StreamBuffer ?? new StreamBuffer(stream);
// Try to read the header.
Id3v2Header headerOrFooter = ReadHeader(sb, tagOrigin);
if (headerOrFooter == null)
return null;
// Don't throw an exception; just return here. The read header could be a false match.
if (headerOrFooter.Size > Id3v2Tag.MaxAllowedSize)
return null;
// Copy header values.
Id3v2Tag tag = new Id3v2Tag(headerOrFooter.Version, headerOrFooter.Flags);
bool isHeader = String.Equals(Id3v2Tag.HeaderIdentifier, headerOrFooter.Identifier, StringComparison.OrdinalIgnoreCase);
// startOffset: offset the header starts
// endOffset: offset the footer ends if available, or when the tag ends
long startOffset, endOffset;
Id3v2Header header, footer = null;
if (isHeader)
{
header = headerOrFooter;
startOffset = header.Position;
endOffset = Math.Min(startOffset + Id3v2Tag.HeaderSize + header.Size + (tag.UseFooter ? Id3v2Tag.FooterSize : 0), sb.Length);
if (endOffset > sb.Length)
{
#if DEBUG
throw new EndOfStreamException("Tag at start could not be read: stream is truncated.");
#else
return null;
#endif
}
}
else
{
// We've read the footer.
footer = headerOrFooter;
endOffset = footer.Position + Id3v2Tag.FooterSize;
startOffset = Math.Max(endOffset - Id3v2Tag.FooterSize - footer.Size - Id3v2Tag.HeaderSize, 0);
// Seek to the start of the tag.
sb.Seek(startOffset, SeekOrigin.Begin);
// Read the header; it's location could be off.
header = ReadHeader(sb, TagOrigin.Start);
if (header == null)
{
// Seek back a bit more and try again.
startOffset = Math.Max(startOffset - Id3v2Tag.HeaderSize, 0);
sb.Seek(startOffset, SeekOrigin.Begin);
header = ReadHeader(sb, TagOrigin.End);
// If we still didn't find a header, seek to the start offset; the header could be missing.
if (header == null)
sb.Seek(startOffset, SeekOrigin.Begin);
}
// If we've found a header.
if (header != null)
{
startOffset = header.Position;
// Calculate the tag size (i.e. all data, excluding the header and footer)
headerOrFooter.Size = (int)Math.Max(endOffset - (startOffset + Id3v2Tag.HeaderSize + Id3v2Tag.FooterSize), 0);
}
else
{
// No header found.
tag.UseHeader = false;
}
// Return if this is the case.
if (headerOrFooter.Size > Id3v2Tag.MaxAllowedSize)
{
#if DEBUG
throw new InvalidDataException(String.Format("Size ({0}) is larger than the max allowed size ({1})", footer.Size, Id3v2Tag.MaxAllowedSize));
#else
return null;
#endif
}
// A footer is read at this point.
tag.UseFooter = true;
}
// At this point, the stream position is located right at the start of the data after the header.
// The size is the sum of the byte length of the extended header, the padding and the frames after unsynchronization.
// This does not include the footer size nor the header size.
int totalSizeItems = Math.Min(headerOrFooter.Size, (int)(sb.Length - sb.Position));
// If the tag has been unsynchronized, synchronize it again.
// For version Id3v2.4.0 and later we don't do the unsynch here:
// unsynchronization [S:6.1] is done on frame level, instead of on tag level, making it easier to skip frames, increasing the stream ability of the tag.
// The unsynchronization flag in the header [S:3.1] indicates if all frames has been unsynchronized,
// while the new unsynchronization flag in the frame header [S:4.1.2] indicates unsynchronization.
if (tag.UseUnsynchronization && (tag.Version < Id3v2Version.Id3v240))
{
int unsynchronizedDataSize = totalSizeItems;
byte[] unsynchronizedData = new byte[unsynchronizedDataSize];
unsynchronizedDataSize = sb.Read(unsynchronizedData, 0, unsynchronizedDataSize);
byte[] data = Id3v2Tag.GetSynchronizedData(unsynchronizedData, 0, unsynchronizedDataSize);
sb = new StreamBuffer(data);
// Update the total size of the items with the length of the synchronized data
totalSizeItems = data.Length;
}
// Calculate the padding size.
int paddingSize = 0;
// Check for an extended header.
if (tag.UseExtendedHeader)
{
int crc;
tag.ExtendedHeader = ReadExtendedHeader(sb, tag, out crc);
if (tag.ExtendedHeader != null)
{
if (tag.UseFooter && (tag.ExtendedHeader.PaddingSize != 0))
{
// Id3v2 tag can not have padding when an Id3v2 footer has been added.
tag.ExtendedHeader.PaddingSize = 0;
}
paddingSize += tag.ExtendedHeader.PaddingSize;
// Calculate CRC if needed.
if (tag.ExtendedHeader.CrcDataPresent)
{
long currentPosition = sb.Position;
// Id3v2.3.0:
// The CRC should be calculated before unsynchronisation on the data between the extended header and the padding, i.e. the frames and only the frames.
// Id3v2.4.0:
// The CRC is calculated on all the data between the header and footer as indicated by the header's tag length field, minus the extended header.
// Note that this includes the padding (if there is any), but excludes the footer.
int dataLength = ((tag.Version >= Id3v2Version.Id3v240)
? totalSizeItems
: totalSizeItems - (tag.PaddingSize + tag.ExtendedHeader.PaddingSize) - 4)
- tag.ExtendedHeader.GetHeaderSize(tag.Version);
byte[] crcData = sb.ToByteArray().Skip((int)currentPosition).Take(dataLength).ToArray();
int calculatedCrc = Cryptography.Crc32.Calculate(crcData);
if (calculatedCrc != crc)
throw new InvalidDataException(String.Format("CRC {0:X} in tag does not match calculated CRC {1:X}", crc, calculatedCrc));
sb.Position = currentPosition;
}
}
}
// Bytes we won't read or have already read, excluding the header/footer.
totalSizeItems -= (tag.ExtendedHeader != null ? tag.ExtendedHeader.GetHeaderSize(tag.Version) + paddingSize : 0);
// Now let's get to the good part, and start parsing the frames!
List<Id3v2Frame> frames = new List<Id3v2Frame>();
long bytesRead = 0;
while (bytesRead < totalSizeItems)
{
long startPosition = sb.Position;
// See if the next byte is a padding byte.
int identifierByte = sb.ReadByte(false);
if (identifierByte == 0x00)
{
// Rest is padding.
// We add up to the padding rather than assigning it, because the ExtendedHeader might include padding as well.
tag.PaddingSize += (int)(totalSizeItems - bytesRead);
bytesRead += tag.PaddingSize;
break;
}
Id3v2Frame frame = Id3v2Frame.ReadFromStream(tag.Version, sb, totalSizeItems - bytesRead);
if (frame != null)
{
Id3v2FrameParseEventArgs frameParseEventArgs = new Id3v2FrameParseEventArgs(frame);
OnFrameParse(frameParseEventArgs);
if (!frameParseEventArgs.Cancel)
{
// If the event has 'replaced' the frame, assign the 'new' frame here and continue.
if (frameParseEventArgs.Frame != null)
frame = frameParseEventArgs.Frame;
// Assign the cryptor instance of the tag to the frame, and decrypt if necessary.
bool isEncrypted = frame.UseEncryption;
if (isEncrypted)
isEncrypted = frame.Decrypt();
// Do the same with decompressing, if necessary.
if (!isEncrypted && frame.UseCompression)
frame.Decompress();
// Call after read event.
Id3v2FrameParsedEventArgs frameParsedEventArgs = new Id3v2FrameParsedEventArgs(frame);
OnFrameParsed(frameParsedEventArgs);
// Add the 'final' frame from the event.
frames.Add(frameParsedEventArgs.Frame);
}
}
else
{
// Skip next byte.
sb.Position = (startPosition + 1);
}
//Reading is always done forward; not backwards.
bytesRead += (sb.Position - startPosition);
}
paddingSize += tag.PaddingSize;
#if DEBUG
if (frames.Count() > Id3v2Tag.MaxAllowedFrames)
{
throw new InvalidDataException(
String.Format("Tag has more frames ('{0}') than the allowed max frames count ('{1}').", frames.Count(), Id3v2Tag.MaxAllowedFrames));
}
if (bytesRead != totalSizeItems)
{
throw new InvalidDataException(
String.Format("Amount of bytes read ({0}) does not match expected size ({1}).", bytesRead, totalSizeItems));
}
// Id3v2.4.0 and later do not have a field for padding size.
if (!isHeader && (paddingSize > 0))
throw new InvalidDataException("Id3v2 tag can not have padding when footer is set.");
#endif
// If the tag is at the start of the stream, is the tag allowed to have a footer?
if (isHeader && tag.UseFooter)
{
sb.Position += Id3v2Tag.FooterSize;
footer = ReadHeader(sb, TagOrigin.End);
}
// Validate the padding.
if (paddingSize > 0)
{
byte[] padding = new byte[paddingSize];
sb.Read(padding, paddingSize);
#if DEBUG
if (!padding.Any(b => b == 0x00))
throw new InvalidDataException("Padding contains one or more invalid padding bytes.");
#endif
}
ValidateHeader(tag, header, footer);
// Sort frames and add them to the tag.
AddRequiredFrames(tag.Version, frames);
tag.SetFrames(frames);
return new AudioTagOffset(tagOrigin, startOffset, endOffset, tag);
}
