Struct MmapDataSource 

pub struct MmapDataSource { /* private fields */ }

A read-only DataSource backed by a memory-mapped file.

The mapping is created once at construction time using memmap2::Mmap. Random-access reads through DataSource::read_range copy the requested bytes; zero-copy access is available via MmapDataSource::as_bytes and MmapDataSource::read_at.

The struct also implements std::io::Read and std::io::Seek so that it can be passed to any reader that accepts R: Read + Seek. The internal cursor used by those trait impls is independent of the DataSource API.

Safety

Internally this calls unsafe { memmap2::Mmap::map(&file) }. The invariant is: the file must not be modified through any other handle while the mapping is live. Violating this invariant causes undefined behaviour.

Implementations

impl MmapDataSource

pub fn open(path: impl AsRef<Path>) -> Result<Self>

Opens path for read-only memory-mapped access.

Errors

Returns an error if the file cannot be opened, its metadata cannot be read, or mmap fails.

pub fn len(&self) -> usize

Returns the total mapped length in bytes (0 for empty files).

pub fn is_empty(&self) -> bool

Returns true if the mapped file is empty.

pub fn as_bytes(&self) -> &[u8]

Returns a byte slice of the entire mapping.

For empty files this returns an empty slice.

pub fn read_at(&self, offset: usize, len: usize) -> Result<&[u8]>

Returns a byte slice for offset..offset+len without moving the internal cursor.

Errors

Returns OxiGdalError::OutOfBounds if offset + len > self.len().

pub fn path(&self) -> &Path

Returns the path of the underlying file.

Trait Implementations

impl DataSource for MmapDataSource

fn size(&self) -> Result<u64>

Returns the total size of the data source in bytes

fn read_range(&self, range: ByteRange) -> Result<Vec<u8>>

Reads bytes from the specified range

fn supports_range_requests(&self) -> bool

Returns true if this data source supports range requests

fn read_ranges(&self, ranges: &[ByteRange]) -> Result<Vec<Vec<u8>>>

Reads bytes from multiple ranges (for optimization)

impl Debug for MmapDataSource

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Read for MmapDataSource

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.

impl Seek for MmapDataSource

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

Seek to an offset, in bytes, in a stream.

fn rewind(&mut self) -> Result<(), Error>

Rewind to the beginning of a stream.

fn stream_len(&mut self) -> Result<u64, Error>

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

Returns the length of this stream (in bytes).

fn stream_position(&mut self) -> Result<u64, Error>

Returns the current seek position from the start of the stream.

fn seek_relative(&mut self, offset: i64) -> Result<(), Error>

Seeks relative to the current position.