mp4ameta 0.13.0

A library for reading and writing iTunes style MPEG-4 audio metadata.
Documentation 
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use super::*;

/// A struct storing size of an atom and whether it is extended.
///
/// ```md
/// 4 bytes standard length
/// 4 bytes identifier
/// 8 bytes optional extended length
/// ```
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct Size {
    ext: bool,
    len: u64,
}

impl Size {
    pub const fn new(ext: bool, content_len: u64) -> Self {
        let len = if ext { content_len + Head::EXT_SIZE } else { content_len + Head::NORMAL_SIZE };
        Self { ext, len }
    }

    pub const fn from(content_len: u64) -> Self {
        let ext = content_len + Head::NORMAL_SIZE > u32::MAX as u64;
        Self::new(ext, content_len)
    }

    /// Whether the head is of standard size (8 bytes) with a 32 bit length or extended (16 bytes)
    /// with a 64 bit length.
    pub const fn ext(&self) -> bool {
        self.ext
    }

    /// The length including the atom's head.
    pub const fn len(&self) -> u64 {
        self.len
    }

    /// The length of the atom's head.
    pub const fn head_len(&self) -> u64 {
        match self.ext {
            true => Head::EXT_SIZE,
            false => Head::NORMAL_SIZE,
        }
    }

    /// The length excluding the atom's head.
    pub const fn content_len(&self) -> u64 {
        self.len - self.head_len()
    }
}

/// A head specifying the size and type of an atom.
///
/// ```md
/// 4 bytes standard length
/// 4 bytes identifier
/// 8 bytes optional extended length
/// ```
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct Head {
    size: Size,
    fourcc: Fourcc,
}

impl Deref for Head {
    type Target = Size;

    fn deref(&self) -> &Self::Target {
        &self.size
    }
}

impl Head {
    pub const NORMAL_SIZE: u64 = 8;
    pub const EXT_SIZE: u64 = 16;

    pub const fn new(ext: bool, len: u64, fourcc: Fourcc) -> Self {
        Self { size: Size { ext, len }, fourcc }
    }

    pub const fn from(size: Size, fourcc: Fourcc) -> Self {
        Self { size, fourcc }
    }

    pub const fn size(&self) -> Size {
        self.size
    }

    pub const fn fourcc(&self) -> Fourcc {
        self.fourcc
    }
}

/// Attempts to parse the atom's head containing a 32 bit unsigned integer determining the size of
/// the atom in bytes and the following 4 byte identifier from the reader. If the 32 bit length is
/// set to 1 an extended 64 bit length is read.
///
/// ```md
/// 4 bytes standard length
/// 4 bytes identifier
/// 8 bytes optional extended length
/// ```
pub fn parse(reader: &mut impl Read, remaining_bytes: u64) -> crate::Result<Head> {
    let mut buf = [[0u8; 4]; 2];

    // SAFETY: the buffer has the same size and alignment
    let byte_buf: &mut [u8; 8] = unsafe { std::mem::transmute(&mut buf) };

    reader
        .read_exact(byte_buf)
        .map_err(|e| crate::Error::new(ErrorKind::Io(e), "Error reading atom head"))?;

    let mut len = u32::from_be_bytes(buf[0]) as u64;
    let fourcc = Fourcc(buf[1]);

    let ext = if len == 1 {
        match reader.read_be_u64() {
            Ok(ext_len) if ext_len < 16 => {
                return Err(crate::Error::new(
                    crate::ErrorKind::InvalidAtomSize,
                    format!(
                        "Read extended length of '{fourcc}' which is less than 16 bytes: {ext_len}"
                    ),
                ));
            }
            Ok(ext_len) => len = ext_len,
            Err(e) => {
                return Err(crate::Error::new(
                    ErrorKind::Io(e),
                    "Error reading extended atom length",
                ));
            }
        }
        true
    } else if len < 8 {
        return Err(crate::Error::new(
            crate::ErrorKind::InvalidAtomSize,
            format!("Read length of '{fourcc}' which is less than 8 bytes: {len}"),
        ));
    } else {
        false
    };

    if len > remaining_bytes {
        return Err(crate::Error::new(
            ErrorKind::AtomSizeOutOfBounds,
            format!(
                "Atom size {len} of {fourcc} out larger than the remaining number of bytes {remaining_bytes}"
            ),
        ));
    }

    Ok(Head::new(ext, len, fourcc))
}

pub fn write(writer: &mut impl Write, head: Head) -> crate::Result<()> {
    if head.ext {
        writer.write_be_u32(1)?;
        writer.write_all(&*head.fourcc)?;
        writer.write_be_u64(head.len())?;
    } else {
        writer.write_be_u32(head.len() as u32)?;
        writer.write_all(&*head.fourcc)?;
    }
    Ok(())
}

/// Attempts to parse a full atom head.
///
/// ```md
/// 1 byte version
/// 3 bytes flags
/// ```
pub fn parse_full(reader: &mut impl Read) -> crate::Result<(u8, [u8; 3])> {
    let mut buf = [0; 4];
    reader.read_exact(&mut buf).map_err(|e| {
        crate::Error::new(
            crate::ErrorKind::Io(e),
            "Error reading version and flags of full atom head",
        )
    })?;
    let [version, flags @ ..] = buf;
    Ok((version, flags))
}

pub fn write_full(writer: &mut impl Write, version: u8, flags: [u8; 3]) -> crate::Result<()> {
    writer.write_all(&[version])?;
    writer.write_all(&flags)?;
    Ok(())
}

#[derive(Clone, Debug, Default, PartialEq, Eq)]
pub struct AtomBounds {
    pos: u64,
    size: Size,
}

impl Deref for AtomBounds {
    type Target = Size;

    fn deref(&self) -> &Self::Target {
        &self.size
    }
}

impl AtomBounds {
    pub const fn pos(&self) -> u64 {
        self.pos
    }

    pub fn content_pos(&self) -> u64 {
        self.pos + self.head_len()
    }

    pub fn end(&self) -> u64 {
        self.pos + self.len()
    }
}

pub fn find_bounds(reader: &mut impl Seek, size: Size) -> crate::Result<AtomBounds> {
    let pos = reader.stream_position()? - size.head_len();
    Ok(AtomBounds { pos, size })
}