Struct LazyCache 

pub struct LazyCache<R>
where
    R: Read + Seek,
{ /* private fields */ }

A lazy-loading cache reader with a multi-tiered caching strategy.

Wraps a Read + Seek type and provides efficient cached reads using a hierarchy of caches: hot (head/tail), warm (memory-mapped), and cold (direct).

The cache automatically loads data in blocks as needed, minimizing I/O operations for sequential and random access patterns.

Cache Tiers

• Hot cache: Small buffers at the head and tail of the source, always available.
• Warm cache: Memory-mapped region for frequently accessed data.
• Cold cache: Fallback buffer for reads that don’t fit in other caches.

See LazyCache::from_read_seek, LazyCache::open, LazyCache::with_hot_cache, and LazyCache::with_warm_cache for construction.

Implementations

impl LazyCache<File>

pub fn open<P: AsRef<Path>>(path: P) -> Result<Self, Error>

Opens a file and creates a new LazyCache for it.

This is a convenience constructor equivalent to calling LazyCache::from_read_seek with a File.

Errors

Returns an error if the file cannot be opened.

Examples

use pure_magic::readers::LazyCache;
use std::path::Path;

let cache = LazyCache::<std::fs::File>::open(Path::new("file.bin"))?;

impl<R> LazyCache<R>

where R: Read + Seek,

pub fn from_read_seek(rs: R) -> Result<Self, Error>

Creates a new LazyCache wrapping a Read + Seek type.

The cache is initialized with default settings: no hot or warm caches. Use LazyCache::with_hot_cache and LazyCache::with_warm_cache to enable additional cache tiers.

Errors

Returns an error if seeking to the end of the source fails.

Examples

use pure_magic::readers::{LazyCache, DataRead};
use std::io::Cursor;

let data = b"hello world";
let cache = LazyCache::from_read_seek(Cursor::new(data)).unwrap();
assert_eq!(cache.data_size(), data.len() as u64);

pub fn with_hot_cache(self, size: usize) -> Result<Self, Error>

Enables the hot cache with the specified size.

The hot cache maintains two buffers: one at the head (beginning) and one at the tail (end) of the source, each with size size / 2. This is useful for optimizing access to the start and end of files.

Errors

Returns an error if seeking or reading from the source fails.

pub fn with_warm_cache(self, warm_size: u64) -> Self

Enables the warm cache with the specified size.

The warm cache uses memory-mapped storage for improved performance when reading larger regions. The size is clamped to be at least as large as the block size to ensure proper alignment.

Note: The memory mapping is performed lazily on first access.

Trait Implementations

impl<R> DataRead for LazyCache<R>

where R: Read + Seek,

fn stream_position(&self) -> u64

Returns the current position in the data stream.

fn read_range(&mut self, range: Range<u64>) -> Result<&[u8], Error>

Reads a range of bytes from the data.

fn read_until_any_delim_or_limit( &mut self, delims: &[u8], limit: u64, ) -> Result<&[u8], Error>

Reads bytes until any of the delimiters or limit bytes is reached.

fn read_until_or_limit(&mut self, byte: u8, limit: u64) -> Result<&[u8], Error>

Reads bytes until byte or limit bytes is reached.

fn read_while_or_limit<F>(&mut self, f: F, limit: u64) -> Result<&[u8], Error>

where F: Fn(u8) -> bool,

Reads bytes while f returns true or until limit bytes is reached.

fn read_until_utf16_or_limit( &mut self, utf16_char: &[u8; 2], limit: u64, ) -> Result<&[u8], Error>

Reads bytes until a UTF-16 character or limit bytes is reached.

fn data_size(&self) -> u64

Returns the total size of the data in bytes.

fn seek(&mut self, pos: SeekFrom) -> Result<u64>

Sets the position for future reads.

fn offset_from_start(&self, pos: SeekFrom) -> u64

Computes the absolute byte offset from a SeekFrom position.

fn read_count(&mut self, count: u64) -> Result<&[u8], Error>

Reads up to count bytes from the current position.

fn read_exact_range(&mut self, range: Range<u64>) -> Result<&[u8], Error>

Reads exactly the specified byte range.

fn read_exact_count(&mut self, count: u64) -> Result<&[u8], Error>

Reads exactly count bytes from the current position.

fn read_exact_into(&mut self, buf: &mut [u8]) -> Result<(), Error>

Reads exactly enough bytes to fill buf.

impl<R> Read for LazyCache<R>

where R: Read + Seek,

fn read(&mut self, buf: &mut [u8]) -> Result<usize>

Pull some bytes from this source into the specified buffer, returning how many bytes were read.

fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize, Error>

Like read, except that it reads into a slice of buffers.

fn is_read_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector)

Determines if this Reader has an efficient read_vectored implementation.

fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize, Error>

Reads all bytes until EOF in this source, placing them into buf.

fn read_to_string(&mut self, buf: &mut String) -> Result<usize, Error>

Reads all bytes until EOF in this source, appending them to buf.

fn read_exact(&mut self, buf: &mut [u8]) -> Result<(), Error>

Reads the exact number of bytes required to fill buf.

fn read_buf(&mut self, buf: BorrowedCursor<'_>) -> Result<(), Error>

🔬This is a nightly-only experimental API. (read_buf)

Pull some bytes from this source into the specified buffer.

fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<(), Error>

🔬This is a nightly-only experimental API. (read_buf)

Reads the exact number of bytes required to fill cursor.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adapter for this instance of Read.

fn bytes(self) -> Bytes<Self>

where Self: Sized,

Transforms this Read instance to an Iterator over its bytes.

fn chain<R>(self, next: R) -> Chain<Self, R>

where R: Read, Self: Sized,

Creates an adapter which will chain this stream with another.

fn take(self, limit: u64) -> Take<Self>

where Self: Sized,

Creates an adapter which will read at most limit bytes from it.

fn read_array<const N: usize>(&mut self) -> Result<[u8; N], Error>

where Self: Sized,

🔬This is a nightly-only experimental API. (read_array)

Read and return a fixed array of bytes from this source.