read_zip.rs

use rc_zip::{
    error::Error,
    fsm::{ArchiveFsm, FsmResult},
    parse::Archive,
};
use rc_zip::{fsm::EntryFsm, parse::Entry};
use tracing::trace;

use crate::entry_reader::EntryReader;
use crate::streaming_entry_reader::StreamingEntryReader;
use std::{io::Read, ops::Deref};

/// A trait for reading something as a zip archive
///
/// See also [ReadZip].
pub trait ReadZipWithSize {
    /// The type of the file to read from.
    type File: HasCursor;

    /// Reads self as a zip archive.
    fn read_zip_with_size(&self, size: u64) -> Result<ArchiveHandle<'_, Self::File>, Error>;
}

/// A trait for reading something as a zip archive when we can tell size from
/// self.
///
/// See also [ReadZipWithSize].
pub trait ReadZip {
    /// The type of the file to read from.
    type File: HasCursor;

    /// Reads self as a zip archive.
    fn read_zip(&self) -> Result<ArchiveHandle<'_, Self::File>, Error>;
}

impl<F> ReadZipWithSize for F
where
    F: HasCursor,
{
    type File = F;

    fn read_zip_with_size(&self, size: u64) -> Result<ArchiveHandle<'_, F>, Error> {
        struct CursorState<'a, F: HasCursor + 'a> {
            cursor: <F as HasCursor>::Cursor<'a>,
            offset: u64,
        }
        let mut cstate: Option<CursorState<'_, F>> = None;

        let mut fsm = ArchiveFsm::new(size);
        loop {
            if let Some(offset) = fsm.wants_read() {
                trace!(%offset, "read_zip_with_size: wants_read, space len = {}", fsm.space().len());

                let mut cstate_next = match cstate.take() {
                    Some(cstate) => {
                        if cstate.offset == offset {
                            // all good, re-using
                            cstate
                        } else {
                            CursorState {
                                cursor: self.cursor_at(offset),
                                offset,
                            }
                        }
                    }
                    None => CursorState {
                        cursor: self.cursor_at(offset),
                        offset,
                    },
                };

                match cstate_next.cursor.read(fsm.space()) {
                    Ok(read_bytes) => {
                        cstate_next.offset += read_bytes as u64;
                        cstate = Some(cstate_next);

                        trace!(%read_bytes, "read_zip_with_size: read");
                        if read_bytes == 0 {
                            return Err(Error::IO(std::io::ErrorKind::UnexpectedEof.into()));
                        }
                        fsm.fill(read_bytes);
                    }
                    Err(err) => return Err(Error::IO(err)),
                }
            }

            fsm = match fsm.process()? {
                FsmResult::Done(archive) => {
                    trace!("read_zip_with_size: done");
                    return Ok(ArchiveHandle {
                        file: self,
                        archive,
                    });
                }
                FsmResult::Continue(fsm) => fsm,
            }
        }
    }
}

impl ReadZip for &[u8] {
    type File = Self;

    fn read_zip(&self) -> Result<ArchiveHandle<'_, Self::File>, Error> {
        self.read_zip_with_size(self.len() as u64)
    }
}

impl ReadZip for Vec<u8> {
    type File = Self;

    fn read_zip(&self) -> Result<ArchiveHandle<'_, Self::File>, Error> {
        self.read_zip_with_size(self.len() as u64)
    }
}

/// A zip archive, read synchronously from a file or other I/O resource.
///
/// This only contains metadata for the archive and its entries. Separate
/// readers can be created for arbitraries entries on-demand using
/// [EntryHandle::reader].
pub struct ArchiveHandle<'a, F>
where
    F: HasCursor,
{
    file: &'a F,
    archive: Archive,
}

impl<F> Deref for ArchiveHandle<'_, F>
where
    F: HasCursor,
{
    type Target = Archive;

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

impl<F> ArchiveHandle<'_, F>
where
    F: HasCursor,
{
    /// Iterate over all files in this zip, read from the central directory.
    pub fn entries(&self) -> impl Iterator<Item = EntryHandle<'_, F>> {
        self.archive.entries().map(move |entry| EntryHandle {
            file: self.file,
            entry,
        })
    }

    /// Attempts to look up an entry by name. This is usually a bad idea,
    /// as names aren't necessarily normalized in zip archives.
    pub fn by_name<N: AsRef<str>>(&self, name: N) -> Option<EntryHandle<'_, F>> {
        self.archive
            .entries()
            .find(|&x| x.name == name.as_ref())
            .map(|entry| EntryHandle {
                file: self.file,
                entry,
            })
    }
}

/// A zip entry, read synchronously from a file or other I/O resource.
pub struct EntryHandle<'a, F> {
    file: &'a F,
    entry: &'a Entry,
}

impl<F> Deref for EntryHandle<'_, F> {
    type Target = Entry;

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

impl<'a, F> EntryHandle<'a, F>
where
    F: HasCursor,
{
    /// Returns a reader for the entry.
    pub fn reader(&self) -> EntryReader<<F as HasCursor>::Cursor<'a>> {
        EntryReader::new(self.entry, self.file.cursor_at(self.entry.header_offset))
    }

    /// Reads the entire entry into a vector.
    pub fn bytes(&self) -> std::io::Result<Vec<u8>> {
        let mut v = Vec::new();
        self.reader().read_to_end(&mut v)?;
        Ok(v)
    }
}

/// A sliceable I/O resource: we can ask for a [Read] at a given offset.
pub trait HasCursor {
    /// The type of [Read] returned by [HasCursor::cursor_at].
    type Cursor<'a>: Read + 'a
    where
        Self: 'a;

    /// Returns a [Read] at the given offset.
    fn cursor_at(&self, offset: u64) -> Self::Cursor<'_>;
}

impl HasCursor for &[u8] {
    type Cursor<'a> = &'a [u8]
    where
        Self: 'a;

    fn cursor_at(&self, offset: u64) -> Self::Cursor<'_> {
        &self[offset.try_into().unwrap()..]
    }
}

impl HasCursor for Vec<u8> {
    type Cursor<'a> = &'a [u8]
    where
        Self: 'a;

    fn cursor_at(&self, offset: u64) -> Self::Cursor<'_> {
        &self[offset.try_into().unwrap()..]
    }
}

#[cfg(feature = "file")]
impl HasCursor for std::fs::File {
    type Cursor<'a> = positioned_io::Cursor<&'a std::fs::File>
    where
        Self: 'a;

    fn cursor_at(&self, offset: u64) -> Self::Cursor<'_> {
        positioned_io::Cursor::new_pos(self, offset)
    }
}

#[cfg(feature = "file")]
impl ReadZip for std::fs::File {
    type File = Self;

    fn read_zip(&self) -> Result<ArchiveHandle<'_, Self>, Error> {
        let size = self.metadata()?.len();
        self.read_zip_with_size(size)
    }
}

/// Allows reading zip entries in a streaming fashion, without seeking,
/// based only on local headers. THIS IS NOT RECOMMENDED, as correctly
/// reading zip files requires reading the central directory (located at
/// the end of the file).
pub trait ReadZipStreaming<R>
where
    R: Read,
{
    /// Get the first zip entry from the stream as a [StreamingEntryReader].
    ///
    /// See the trait's documentation for why using this is
    /// generally a bad idea: you might want to use [ReadZip] or
    /// [ReadZipWithSize] instead.
    fn stream_zip_entries_throwing_caution_to_the_wind(
        self,
    ) -> Result<StreamingEntryReader<R>, Error>;
}

impl<R> ReadZipStreaming<R> for R
where
    R: Read,
{
    fn stream_zip_entries_throwing_caution_to_the_wind(
        mut self,
    ) -> Result<StreamingEntryReader<Self>, Error> {
        let mut fsm = EntryFsm::new(None, None);

        loop {
            if fsm.wants_read() {
                let n = self.read(fsm.space())?;
                trace!("read {} bytes into buf for first zip entry", n);
                fsm.fill(n);
            }

            if let Some(entry) = fsm.process_till_header()? {
                let entry = entry.clone();
                return Ok(StreamingEntryReader::new(fsm, entry, self));
            }
        }
    }
}