zip-rs-wasm/src/spec.rs

#![macro_use]

use crate::result::{ZipError, ZipResult};
use core::mem;
use memchr::memmem::FinderRev;
use std::io;
use std::io::prelude::*;
use std::rc::Rc;
use std::slice;

/// "Magic" header values used in the zip spec to locate metadata records.
///
/// These values currently always take up a fixed four bytes, so we can parse and wrap them in this
/// struct to enforce some small amount of type safety.
#[derive(Copy, Clone, Debug, PartialOrd, Ord, PartialEq, Eq, Hash)]
#[repr(transparent)]
pub(crate) struct Magic(u32);

impl Magic {
    pub const fn literal(x: u32) -> Self {
        Self(x)
    }

    #[inline(always)]
    pub const fn from_le_bytes(bytes: [u8; 4]) -> Self {
        Self(u32::from_le_bytes(bytes))
    }

    #[inline(always)]
    pub const fn to_le_bytes(self) -> [u8; 4] {
        self.0.to_le_bytes()
    }

    #[allow(clippy::wrong_self_convention)]
    #[inline(always)]
    pub fn from_le(self) -> Self {
        Self(u32::from_le(self.0))
    }

    #[allow(clippy::wrong_self_convention)]
    #[inline(always)]
    pub fn to_le(self) -> Self {
        Self(u32::to_le(self.0))
    }

    pub const LOCAL_FILE_HEADER_SIGNATURE: Self = Self::literal(0x04034b50);
    pub const CENTRAL_DIRECTORY_HEADER_SIGNATURE: Self = Self::literal(0x02014b50);
    pub const CENTRAL_DIRECTORY_END_SIGNATURE: Self = Self::literal(0x06054b50);
    pub const ZIP64_CENTRAL_DIRECTORY_END_SIGNATURE: Self = Self::literal(0x06064b50);
    pub const ZIP64_CENTRAL_DIRECTORY_END_LOCATOR_SIGNATURE: Self = Self::literal(0x07064b50);
}

/// Similar to [`Magic`], but used for extra field tags as per section 4.5.3 of APPNOTE.TXT.
#[derive(Copy, Clone, Debug, PartialOrd, Ord, PartialEq, Eq, Hash)]
#[repr(transparent)]
pub(crate) struct ExtraFieldMagic(u16);

/* TODO: maybe try to use this for parsing extra fields as well as writing them? */
#[allow(dead_code)]
impl ExtraFieldMagic {
    pub const fn literal(x: u16) -> Self {
        Self(x)
    }

    #[inline(always)]
    pub const fn from_le_bytes(bytes: [u8; 2]) -> Self {
        Self(u16::from_le_bytes(bytes))
    }

    #[inline(always)]
    pub const fn to_le_bytes(self) -> [u8; 2] {
        self.0.to_le_bytes()
    }

    #[allow(clippy::wrong_self_convention)]
    #[inline(always)]
    pub fn from_le(self) -> Self {
        Self(u16::from_le(self.0))
    }

    #[allow(clippy::wrong_self_convention)]
    #[inline(always)]
    pub fn to_le(self) -> Self {
        Self(u16::to_le(self.0))
    }

    pub const ZIP64_EXTRA_FIELD_TAG: Self = Self::literal(0x0001);
}

/// The file size at which a ZIP64 record becomes necessary.
///
/// If a file larger than this threshold attempts to be written, compressed or uncompressed, and
/// [`FileOptions::large_file()`](crate::write::FileOptions) was not true, then [`ZipWriter`] will
/// raise an [`io::Error`] with [`io::ErrorKind::Other`].
///
/// If the zip file itself is larger than this value, then a zip64 central directory record will be
/// written to the end of the file.
///
///```
/// # fn main() -> Result<(), zip::result::ZipError> {
/// use std::io::{self, Cursor, prelude::*};
/// use std::error::Error;
/// use zip::{ZipWriter, write::SimpleFileOptions};
///
/// let mut zip = ZipWriter::new(Cursor::new(Vec::new()));
/// // Writing an extremely large file for this test is faster without compression.
/// let options = SimpleFileOptions::default().compression_method(zip::CompressionMethod::Stored);
///
/// let big_len: usize = (zip::ZIP64_BYTES_THR as usize) + 1;
/// let big_buf = vec![0u8; big_len];
/// zip.start_file("zero.dat", options)?;
/// // This is too big!
/// let res = zip.write_all(&big_buf[..]).err().unwrap();
/// assert_eq!(res.kind(), io::ErrorKind::Other);
/// let description = format!("{}", &res);
/// assert_eq!(description, "Large file option has not been set");
/// // Attempting to write anything further to the same zip will still succeed, but the previous
/// // failing entry has been removed.
/// zip.start_file("one.dat", options)?;
/// let zip = zip.finish_into_readable()?;
/// let names: Vec<_> = zip.file_names().collect();
/// assert_eq!(&names, &["one.dat"]);
///
/// // Create a new zip output.
/// let mut zip = ZipWriter::new(Cursor::new(Vec::new()));
/// // This time, create a zip64 record for the file.
/// let options = options.large_file(true);
/// zip.start_file("zero.dat", options)?;
/// // This succeeds because we specified that it could be a large file.
/// assert!(zip.write_all(&big_buf[..]).is_ok());
/// # Ok(())
/// # }
///```
pub const ZIP64_BYTES_THR: u64 = u32::MAX as u64;
/// The number of entries within a single zip necessary to allocate a zip64 central
/// directory record.
///
/// If more than this number of entries is written to a [`ZipWriter`], then [`ZipWriter::finish()`]
/// will write out extra zip64 data to the end of the zip file.
pub const ZIP64_ENTRY_THR: usize = u16::MAX as usize;

/// # Safety
///
/// - No padding/uninit bytes
/// - All bytes patterns must be valid
/// - No cell, pointers
///
/// See `bytemuck::Pod` for more details.
pub(crate) unsafe trait Pod: Copy + 'static {
    #[inline]
    fn zeroed() -> Self {
        unsafe { mem::zeroed() }
    }

    #[inline]
    fn as_bytes(&self) -> &[u8] {
        unsafe { slice::from_raw_parts(self as *const Self as *const u8, mem::size_of::<Self>()) }
    }

    #[inline]
    fn as_bytes_mut(&mut self) -> &mut [u8] {
        unsafe { slice::from_raw_parts_mut(self as *mut Self as *mut u8, mem::size_of::<Self>()) }
    }
}

pub(crate) trait FixedSizeBlock: Pod {
    const MAGIC: Magic;

    fn magic(self) -> Magic;

    const WRONG_MAGIC_ERROR: ZipError;

    #[allow(clippy::wrong_self_convention)]
    fn from_le(self) -> Self;

    fn parse<R: Read>(reader: &mut R) -> ZipResult<Self> {
        let mut block = Self::zeroed();
        reader.read_exact(block.as_bytes_mut())?;
        let block = Self::from_le(block);

        if block.magic() != Self::MAGIC {
            return Err(Self::WRONG_MAGIC_ERROR);
        }
        Ok(block)
    }

    fn to_le(self) -> Self;

    fn write<T: Write>(self, writer: &mut T) -> ZipResult<()> {
        let block = self.to_le();
        writer.write_all(block.as_bytes())?;
        Ok(())
    }
}

/// Convert all the fields of a struct *from* little-endian representations.
macro_rules! from_le {
    ($obj:ident, $field:ident, $type:ty) => {
        $obj.$field = <$type>::from_le($obj.$field);
    };
    ($obj:ident, [($field:ident, $type:ty) $(,)?]) => {
        from_le![$obj, $field, $type];
    };
    ($obj:ident, [($field:ident, $type:ty), $($rest:tt),+ $(,)?]) => {
        from_le![$obj, $field, $type];
        from_le!($obj, [$($rest),+]);
    };
}

/// Convert all the fields of a struct *into* little-endian representations.
macro_rules! to_le {
    ($obj:ident, $field:ident, $type:ty) => {
        $obj.$field = <$type>::to_le($obj.$field);
    };
    ($obj:ident, [($field:ident, $type:ty) $(,)?]) => {
        to_le![$obj, $field, $type];
    };
    ($obj:ident, [($field:ident, $type:ty), $($rest:tt),+ $(,)?]) => {
        to_le![$obj, $field, $type];
        to_le!($obj, [$($rest),+]);
    };
}

/* TODO: derive macro to generate these fields? */
/// Implement `from_le()` and `to_le()`, providing the field specification to both macros
/// and methods.
macro_rules! to_and_from_le {
    ($($args:tt),+ $(,)?) => {
        #[inline(always)]
        fn from_le(mut self) -> Self {
            from_le![self, [$($args),+]];
            self
        }
        #[inline(always)]
        fn to_le(mut self) -> Self {
            to_le![self, [$($args),+]];
            self
        }
    };
}

#[derive(Copy, Clone, Debug)]
#[repr(packed, C)]
pub(crate) struct Zip32CDEBlock {
    magic: Magic,
    pub disk_number: u16,
    pub disk_with_central_directory: u16,
    pub number_of_files_on_this_disk: u16,
    pub number_of_files: u16,
    pub central_directory_size: u32,
    pub central_directory_offset: u32,
    pub zip_file_comment_length: u16,
}

unsafe impl Pod for Zip32CDEBlock {}

impl FixedSizeBlock for Zip32CDEBlock {
    const MAGIC: Magic = Magic::CENTRAL_DIRECTORY_END_SIGNATURE;

    #[inline(always)]
    fn magic(self) -> Magic {
        self.magic
    }

    const WRONG_MAGIC_ERROR: ZipError =
        ZipError::InvalidArchive("Invalid digital signature header");

    to_and_from_le![
        (magic, Magic),
        (disk_number, u16),
        (disk_with_central_directory, u16),
        (number_of_files_on_this_disk, u16),
        (number_of_files, u16),
        (central_directory_size, u32),
        (central_directory_offset, u32),
        (zip_file_comment_length, u16)
    ];
}

#[derive(Debug)]
pub(crate) struct Zip32CentralDirectoryEnd {
    pub disk_number: u16,
    pub disk_with_central_directory: u16,
    pub number_of_files_on_this_disk: u16,
    pub number_of_files: u16,
    pub central_directory_size: u32,
    pub central_directory_offset: u32,
    pub zip_file_comment: Box<[u8]>,
}

impl Zip32CentralDirectoryEnd {
    fn block_and_comment(self) -> ZipResult<(Zip32CDEBlock, Box<[u8]>)> {
        let Self {
            disk_number,
            disk_with_central_directory,
            number_of_files_on_this_disk,
            number_of_files,
            central_directory_size,
            central_directory_offset,
            zip_file_comment,
        } = self;
        let block = Zip32CDEBlock {
            magic: Zip32CDEBlock::MAGIC,
            disk_number,
            disk_with_central_directory,
            number_of_files_on_this_disk,
            number_of_files,
            central_directory_size,
            central_directory_offset,
            zip_file_comment_length: zip_file_comment
                .len()
                .try_into()
                .map_err(|_| ZipError::InvalidArchive("File comment must be less than 64 KiB"))?,
        };
        Ok((block, zip_file_comment))
    }

    pub fn parse<T: Read>(reader: &mut T) -> ZipResult<Zip32CentralDirectoryEnd> {
        let Zip32CDEBlock {
            // magic,
            disk_number,
            disk_with_central_directory,
            number_of_files_on_this_disk,
            number_of_files,
            central_directory_size,
            central_directory_offset,
            zip_file_comment_length,
            ..
        } = Zip32CDEBlock::parse(reader)?;

        let mut zip_file_comment = vec![0u8; zip_file_comment_length as usize].into_boxed_slice();
        reader.read_exact(&mut zip_file_comment)?;

        Ok(Zip32CentralDirectoryEnd {
            disk_number,
            disk_with_central_directory,
            number_of_files_on_this_disk,
            number_of_files,
            central_directory_size,
            central_directory_offset,
            zip_file_comment,
        })
    }

    #[allow(clippy::type_complexity)]
    pub fn find_and_parse<T: Read + Seek>(
        reader: &mut T,
    ) -> ZipResult<Box<[(Rc<Zip32CentralDirectoryEnd>, u64)]>> {
        let mut results = vec![];
        let file_length = reader.seek(io::SeekFrom::End(0))?;

        if file_length < mem::size_of::<Zip32CDEBlock>() as u64 {
            return Err(ZipError::InvalidArchive("Invalid zip header"));
        }

        // The End Of Central Directory Record should be the last thing in
        // the file and so searching the last 65557 bytes of the file should
        // be enough. However, not all zips are well-formed and other
        // programs may consume zips with extra junk at the end without
        // error, so we go back 128K to be compatible with them. 128K is
        // arbitrary, but it matches what Info-Zip does.
        const EOCDR_SEARCH_SIZE: u64 = 128 * 1024;
        let search_lower_bound = file_length.saturating_sub(EOCDR_SEARCH_SIZE);

        const END_WINDOW_SIZE: usize = 8192;
        /* TODO: use static_assertions!() */
        debug_assert!(END_WINDOW_SIZE > mem::size_of::<Magic>());

        const SIG_BYTES: [u8; mem::size_of::<Magic>()] =
            Magic::CENTRAL_DIRECTORY_END_SIGNATURE.to_le_bytes();
        let finder = FinderRev::new(&SIG_BYTES);

        let mut window_start: u64 = file_length.saturating_sub(END_WINDOW_SIZE as u64);
        let mut window = [0u8; END_WINDOW_SIZE];
        while window_start >= search_lower_bound {
            /* Go to the start of the window in the file. */
            reader.seek(io::SeekFrom::Start(window_start))?;

            /* Identify how many bytes to read (this may be less than the window size for files
             * smaller than END_WINDOW_SIZE). */
            let end = (window_start + END_WINDOW_SIZE as u64).min(file_length);
            let cur_len = (end - window_start) as usize;
            debug_assert!(cur_len > 0);
            debug_assert!(cur_len <= END_WINDOW_SIZE);
            let cur_window: &mut [u8] = &mut window[..cur_len];
            /* Read the window into the bytes! */
            reader.read_exact(cur_window)?;

            /* Find instances of the magic signature. */
            for offset in finder.rfind_iter(cur_window) {
                let cde_start_pos = window_start + offset as u64;
                reader.seek(io::SeekFrom::Start(cde_start_pos))?;
                /* Drop any headers that don't parse. */
                if let Ok(cde) = Self::parse(reader) {
                    results.push((Rc::new(cde), cde_start_pos));
                }
            }

            /* We always want to make sure we go allllll the way back to the start of the file if
             * we can't find it elsewhere. However, our `while` condition doesn't check that. So we
             * avoid infinite looping by checking at the end of the loop. */
            if window_start == search_lower_bound {
                break;
            }
            /* Shift the window by END_WINDOW_SIZE bytes, but make sure to cover matches that
             * overlap our nice neat window boundaries! */
            window_start = (window_start
                /* NB: To catch matches across window boundaries, we need to make our blocks overlap
                 * by the width of the pattern to match. */
                + mem::size_of::<Magic>() as u64)
                /* This should never happen, but make sure we don't go past the end of the file. */
                .min(file_length);
            window_start = window_start
                .saturating_sub(
                    /* Shift the window upon each iteration so we search END_WINDOW_SIZE bytes at
                     * once (unless limited by file_length). */
                    END_WINDOW_SIZE as u64,
                )
                /* This will never go below the value of `search_lower_bound`, so we have a special
                 * `if window_start == search_lower_bound` check above. */
                .max(search_lower_bound);
        }
        if results.is_empty() {
            Err(ZipError::InvalidArchive(
                "Could not find central directory end",
            ))
        } else {
            Ok(results.into_boxed_slice())
        }
    }

    pub fn write<T: Write>(self, writer: &mut T) -> ZipResult<()> {
        let (block, comment) = self.block_and_comment()?;
        block.write(writer)?;
        writer.write_all(&comment)?;
        Ok(())
    }
}

#[derive(Copy, Clone)]
#[repr(packed, C)]
pub(crate) struct Zip64CDELocatorBlock {
    magic: Magic,
    pub disk_with_central_directory: u32,
    pub end_of_central_directory_offset: u64,
    pub number_of_disks: u32,
}

unsafe impl Pod for Zip64CDELocatorBlock {}

impl FixedSizeBlock for Zip64CDELocatorBlock {
    const MAGIC: Magic = Magic::ZIP64_CENTRAL_DIRECTORY_END_LOCATOR_SIGNATURE;

    #[inline(always)]
    fn magic(self) -> Magic {
        self.magic
    }

    const WRONG_MAGIC_ERROR: ZipError =
        ZipError::InvalidArchive("Invalid zip64 locator digital signature header");

    to_and_from_le![
        (magic, Magic),
        (disk_with_central_directory, u32),
        (end_of_central_directory_offset, u64),
        (number_of_disks, u32),
    ];
}

pub(crate) struct Zip64CentralDirectoryEndLocator {
    pub disk_with_central_directory: u32,
    pub end_of_central_directory_offset: u64,
    pub number_of_disks: u32,
}

impl Zip64CentralDirectoryEndLocator {
    pub fn parse<T: Read>(reader: &mut T) -> ZipResult<Zip64CentralDirectoryEndLocator> {
        let Zip64CDELocatorBlock {
            // magic,
            disk_with_central_directory,
            end_of_central_directory_offset,
            number_of_disks,
            ..
        } = Zip64CDELocatorBlock::parse(reader)?;

        Ok(Zip64CentralDirectoryEndLocator {
            disk_with_central_directory,
            end_of_central_directory_offset,
            number_of_disks,
        })
    }

    pub fn block(self) -> Zip64CDELocatorBlock {
        let Self {
            disk_with_central_directory,
            end_of_central_directory_offset,
            number_of_disks,
        } = self;
        Zip64CDELocatorBlock {
            magic: Zip64CDELocatorBlock::MAGIC,
            disk_with_central_directory,
            end_of_central_directory_offset,
            number_of_disks,
        }
    }

    pub fn write<T: Write>(self, writer: &mut T) -> ZipResult<()> {
        self.block().write(writer)
    }
}

#[derive(Copy, Clone)]
#[repr(packed, C)]
pub(crate) struct Zip64CDEBlock {
    magic: Magic,
    pub record_size: u64,
    pub version_made_by: u16,
    pub version_needed_to_extract: u16,
    pub disk_number: u32,
    pub disk_with_central_directory: u32,
    pub number_of_files_on_this_disk: u64,
    pub number_of_files: u64,
    pub central_directory_size: u64,
    pub central_directory_offset: u64,
}

unsafe impl Pod for Zip64CDEBlock {}

impl FixedSizeBlock for Zip64CDEBlock {
    const MAGIC: Magic = Magic::ZIP64_CENTRAL_DIRECTORY_END_SIGNATURE;

    fn magic(self) -> Magic {
        self.magic
    }

    const WRONG_MAGIC_ERROR: ZipError =
        ZipError::InvalidArchive("Invalid digital signature header");

    to_and_from_le![
        (magic, Magic),
        (record_size, u64),
        (version_made_by, u16),
        (version_needed_to_extract, u16),
        (disk_number, u32),
        (disk_with_central_directory, u32),
        (number_of_files_on_this_disk, u64),
        (number_of_files, u64),
        (central_directory_size, u64),
        (central_directory_offset, u64),
    ];
}

pub(crate) struct Zip64CentralDirectoryEnd {
    pub version_made_by: u16,
    pub version_needed_to_extract: u16,
    pub disk_number: u32,
    pub disk_with_central_directory: u32,
    pub number_of_files_on_this_disk: u64,
    pub number_of_files: u64,
    pub central_directory_size: u64,
    pub central_directory_offset: u64,
    //pub extensible_data_sector: Vec<u8>, <-- We don't do anything with this at the moment.
}

impl Zip64CentralDirectoryEnd {
    pub fn parse<T: Read>(reader: &mut T) -> ZipResult<Zip64CentralDirectoryEnd> {
        let Zip64CDEBlock {
            // record_size,
            version_made_by,
            version_needed_to_extract,
            disk_number,
            disk_with_central_directory,
            number_of_files_on_this_disk,
            number_of_files,
            central_directory_size,
            central_directory_offset,
            ..
        } = Zip64CDEBlock::parse(reader)?;
        Ok(Self {
            version_made_by,
            version_needed_to_extract,
            disk_number,
            disk_with_central_directory,
            number_of_files_on_this_disk,
            number_of_files,
            central_directory_size,
            central_directory_offset,
        })
    }

    pub fn find_and_parse<T: Read + Seek>(
        reader: &mut T,
        search_lower_bound: u64,
        search_upper_bound: u64,
    ) -> ZipResult<Vec<(Zip64CentralDirectoryEnd, u64)>> {
        let mut results = Vec::new();

        const END_WINDOW_SIZE: usize = 2048;
        /* TODO: use static_assertions!() */
        debug_assert!(END_WINDOW_SIZE > mem::size_of::<Magic>());

        const SIG_BYTES: [u8; mem::size_of::<Magic>()] =
            Magic::ZIP64_CENTRAL_DIRECTORY_END_SIGNATURE.to_le_bytes();
        let finder = FinderRev::new(&SIG_BYTES);

        let mut window_start: u64 = search_upper_bound
            .saturating_sub(END_WINDOW_SIZE as u64)
            .max(search_lower_bound);
        let mut window = [0u8; END_WINDOW_SIZE];
        while window_start >= search_lower_bound {
            reader.seek(io::SeekFrom::Start(window_start))?;

            /* Identify how many bytes to read (this may be less than the window size for files
             * smaller than END_WINDOW_SIZE). */
            let end = (window_start + END_WINDOW_SIZE as u64).min(search_upper_bound);

            debug_assert!(end >= window_start);
            let cur_len = (end - window_start) as usize;
            if cur_len == 0 {
                break;
            }
            debug_assert!(cur_len <= END_WINDOW_SIZE);
            let cur_window: &mut [u8] = &mut window[..cur_len];
            /* Read the window into the bytes! */
            reader.read_exact(cur_window)?;

            /* Find instances of the magic signature. */
            for offset in finder.rfind_iter(cur_window) {
                let cde_start_pos = window_start + offset as u64;
                reader.seek(io::SeekFrom::Start(cde_start_pos))?;

                debug_assert!(cde_start_pos >= search_lower_bound);
                let archive_offset = cde_start_pos - search_lower_bound;
                let cde = Self::parse(reader)?;

                results.push((cde, archive_offset));
            }

            /* We always want to make sure we go allllll the way back to the start of the file if
             * we can't find it elsewhere. However, our `while` condition doesn't check that. So we
             * avoid infinite looping by checking at the end of the loop. */
            if window_start == search_lower_bound {
                break;
            }
            /* Shift the window by END_WINDOW_SIZE bytes, but make sure to cover matches that
             * overlap our nice neat window boundaries! */
            window_start = (window_start
                /* NB: To catch matches across window boundaries, we need to make our blocks overlap
                 * by the width of the pattern to match. */
                + mem::size_of::<Magic>() as u64)
                /* This may never happen, but make sure we don't go past the end of the specified
                 * range. */
                .min(search_upper_bound);
            window_start = window_start
                .saturating_sub(
                    /* Shift the window upon each iteration so we search END_WINDOW_SIZE bytes at
                     * once (unless limited by search_upper_bound). */
                    END_WINDOW_SIZE as u64,
                )
                /* This will never go below the value of `search_lower_bound`, so we have a special
                 * `if window_start == search_lower_bound` check above. */
                .max(search_lower_bound);
        }

        if results.is_empty() {
            Err(ZipError::InvalidArchive(
                "Could not find ZIP64 central directory end",
            ))
        } else {
            Ok(results)
        }
    }

    pub fn block(self) -> Zip64CDEBlock {
        let Self {
            version_made_by,
            version_needed_to_extract,
            disk_number,
            disk_with_central_directory,
            number_of_files_on_this_disk,
            number_of_files,
            central_directory_size,
            central_directory_offset,
        } = self;
        Zip64CDEBlock {
            magic: Zip64CDEBlock::MAGIC,
            /* currently unused */
            record_size: 44,
            version_made_by,
            version_needed_to_extract,
            disk_number,
            disk_with_central_directory,
            number_of_files_on_this_disk,
            number_of_files,
            central_directory_size,
            central_directory_offset,
        }
    }

    pub fn write<T: Write>(self, writer: &mut T) -> ZipResult<()> {
        self.block().write(writer)
    }
}

pub(crate) fn is_dir(filename: &str) -> bool {
    filename
        .chars()
        .next_back()
        .is_some_and(|c| c == '/' || c == '\\')
}

#[cfg(test)]
mod test {
    use super::*;
    use std::io::Cursor;

    #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
    #[repr(packed, C)]
    pub struct TestBlock {
        magic: Magic,
        pub file_name_length: u16,
    }

    unsafe impl Pod for TestBlock {}

    impl FixedSizeBlock for TestBlock {
        const MAGIC: Magic = Magic::literal(0x01111);

        fn magic(self) -> Magic {
            self.magic
        }

        const WRONG_MAGIC_ERROR: ZipError = ZipError::InvalidArchive("unreachable");

        to_and_from_le![(magic, Magic), (file_name_length, u16)];
    }

    /// Demonstrate that a block object can be safely written to memory and deserialized back out.
    #[test]
    fn block_serde() {
        let block = TestBlock {
            magic: TestBlock::MAGIC,
            file_name_length: 3,
        };
        let mut c = Cursor::new(Vec::new());
        block.write(&mut c).unwrap();
        c.set_position(0);
        let block2 = TestBlock::parse(&mut c).unwrap();
        assert_eq!(block, block2);
    }
}