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Add support for readers that implement Seek (#218)
`Archive::new` requires only `Read` for backward-compatibility, while `Archive::new_from_seek` can be used with readers that also implement `Seek`, to allow more efficient skipping over file contents.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,72 @@ | ||
| use std::cmp; | ||
| use std::io; | ||
| use std::io::prelude::*; | ||
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| use crate::other; | ||
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| /// The `SkipRead` trait allows for reading bytes from a source, as well as | ||
| /// skipping over a number of bytes | ||
| /// | ||
| /// This is used for backward compatibility with [`std::io::Read`]. Each reader | ||
| /// automatically implements `SkipRead`. Readers that additionally implement | ||
| /// [`std::io::Seek`] can use `SeekingSkipRead` to implements efficient skipping | ||
| /// based on [`std::io::Seek:seek`]. | ||
| pub trait SkipRead { | ||
| /// Pull some bytes from this source into the specified buffer, returning | ||
| /// how many bytes were read. | ||
| /// | ||
| /// Identical to [`std::io::Read::read`]. | ||
| fn read(&mut self, buf: &mut [u8]) -> io::Result<usize>; | ||
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| /// Skip a specified number of bytes from the source, returning how many | ||
| /// bytes were skipped. | ||
| fn skip(&mut self, amt: u64) -> io::Result<u64>; | ||
| } | ||
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| /// `SkipRead` is implemented for all readers by using [`std::io::Read::read`] | ||
| /// for both reading and skipping. | ||
| impl<R: Read> SkipRead for R { | ||
| fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> { | ||
| self.read(buf) | ||
| } | ||
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| fn skip(&mut self, amt: u64) -> io::Result<u64> { | ||
| let mut buf = [0u8; 4096 * 8]; | ||
| let mut skipped = 0; | ||
| while skipped < amt { | ||
| let n = cmp::min(amt - skipped, buf.len() as u64); | ||
| let n = self.read(&mut buf[..n as usize])?; | ||
| if n == 0 { | ||
| return Err(other("unexpected EOF during skip")); | ||
| } | ||
| skipped += n as u64; | ||
| } | ||
| Ok(skipped) | ||
| } | ||
| } | ||
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| /// Wrapper to implement `SkipRead` more efficiently for readers that also | ||
| /// implement [`std::io::Seek`]. Skipping is implemented using | ||
| /// [`std::io::Seek:seek`]. | ||
| pub struct SeekingSkipRead<R: Read + Seek> { | ||
| inner: R, | ||
| } | ||
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| impl<R: Read + Seek> SeekingSkipRead<R> { | ||
| pub fn new(obj: R) -> SeekingSkipRead<R> { | ||
| SeekingSkipRead { inner: obj } | ||
| } | ||
| } | ||
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| impl<R: Read + Seek> SkipRead for SeekingSkipRead<R> { | ||
| fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> { | ||
| self.inner.read(buf) | ||
| } | ||
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| fn skip(&mut self, amount: u64) -> io::Result<u64> { | ||
| let old_pos = self.inner.stream_position()?; | ||
| self.inner | ||
| .seek(io::SeekFrom::Current(amount as i64)) | ||
| .map(|pos| pos - old_pos) | ||
| } | ||
| } |
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