caj2pdf-core 0.5.0

// SPDX-License-Identifier: MIT

//! A positioned source over a `std::io` handle.
//!
//! `SeekableSource::new(&mut input)` leaves ownership with the caller. Output
//! needs no adapter: the core writes to any `std::io::Write`.

use crate::{Error, MAX_IO_CHUNK, RangedSource, Result};
use std::io::{Read, Seek, SeekFrom};

/// A positioned source backed by a caller-supplied `Read + Seek` handle.
pub struct SeekableSource<R> {
    inner: R,
    size: u64,
}

impl<R: Read + Seek> SeekableSource<R> {
    /// Snapshot the size and restore the handle's original position.
    pub fn new(mut inner: R) -> Result<Self> {
        let original = inner.stream_position()?;
        let size = inner.seek(SeekFrom::End(0))?;
        inner.seek(SeekFrom::Start(original))?;
        Ok(Self { inner, size })
    }

    pub fn into_inner(self) -> R {
        self.inner
    }
}

impl<R: Read + Seek> RangedSource for SeekableSource<R> {
    fn size(&self) -> u64 {
        self.size
    }

    fn read_at(&mut self, offset: u64, destination: &mut [u8]) -> Result<usize> {
        if destination.len() > MAX_IO_CHUNK {
            return Err(Error::limit(
                "I/O request bytes",
                MAX_IO_CHUNK as u64,
                destination.len() as u64,
            ));
        }
        if offset > self.size {
            return Err(Error::invalid("read starts beyond source size"));
        }
        offset
            .checked_add(destination.len() as u64)
            .ok_or(Error::invalid("read end overflows 64-bit offset"))?;
        self.inner.seek(SeekFrom::Start(offset))?;
        Ok(self.inner.read(destination)?)
    }
}