Struct olio::fs::ReadSlice

pub struct ReadSlice<P> where
    P: PosRead,  { /* fields omitted */ }

Re-implements Read and Seek over PosRead using only positioned reads, and by maintaining instance independent start, end, and position.

PosRead is implemented for any Borrow<File> so this can own via ReadSlice<File> or use a shared reference, as in ReadSlice<&File> or ReadSlice<Arc<File>>.

As compared with ReadPos, ReadSlice adds a general start offset, and limits access to the start..end range. Seeks are relative, so a seek to SeekFrom::Start(0) is always the first byte of the slice.

Fixed start and end offsets are passed on construction and used to constrain reads and interpret SeekFrom::Start and SeekFrom::End. These offsets are neither checked against nor updated from the inner PosRead (for example via file metadata) and could deviate if concurrent writes or truncation is possible. Reads beyond end or the end of the inner PosRead will return 0 length. Seeking past the end is allowed by the platforms for File, and is also allowed for ReadSlice.

Methods

impl<P> ReadSlice<P> where     P: PosRead,

pub fn new(pos_read: P, start: u64, end: u64) -> Self

New instance by PosRead instance, fixed start and end offsets. The initial position is at the start (relative offset 0).

pub fn len(&self) -> u64

Return the total size of the slice in bytes. This is based on the start and end offsets as constructed and can differ from the inner PosRead length.

pub fn is_empty(&self) -> bool

Return true if length is 0.

pub fn tell(&self) -> u64

Return the current instance position, relative to the slice. This is a convenience shorthand for seek(SeekFrom::Current(0)), is infallable, and does not require a mutable reference.

impl<P> ReadSlice<P> where     P: PosRead + Clone,

Important traits for ReadSlice<P>

impl<P> Read for ReadSlice<P> where
    P: PosRead, 

pub fn subslice(&self, start: u64, end: u64) -> ReadSlice<P>

Return a new and independent ReadSlice by clone of the inner PosRead, for the range of byte offsets start..end which are relative to, and must be fully contained by self. This implementation panics on overflow, if start..end is not fully contained, or if start is greater-than end.

impl<P> ReadSlice<P> where     P: PosRead + Borrow<File>,

pub fn mem_map(&self) -> Result<Mmap, Error>

Return a new read-only memory map handle Mmap for the complete region of the underlying File, from start to end.

Trait Implementations

impl<P: Debug> Debug for ReadSlice<P> where     P: PosRead,

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

Formats the value using the given formatter.

impl<P> Clone for ReadSlice<P> where     P: PosRead + Clone,

fn clone(&self) -> Self

Return a new, independent ReadSlice by clone of the inner PosRead, with the same start and end as self, and positioned at start.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<P> PosRead for ReadSlice<P> where     P: PosRead,

fn pread(&self, buf: &mut [u8], offset: u64) -> Result<usize>

Read bytes, starting at the specified offset, into the specified buffer and return the number of bytes read. The offset is from the start of the underlying file or file range. Reads beyond the end of available bytes will return 0 length. The position of the underlying file pointer (aka cursor) is not used. It is platform dependent whether the underlying file pointer is modified by this operation.

impl<P> Read for ReadSlice<P> where     P: PosRead,

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.

unsafe fn initializer(&self) -> Initializer

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

Determines if this Reader can work with buffers of uninitialized memory.

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

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

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

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

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

Read the exact number of bytes required to fill buf.

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

Creates a "by reference" adaptor for this instance of Read.

fn bytes(self) -> Bytes<Self>

Transforms this Read instance to an [Iterator] over its bytes.

fn chars(self) -> Chars<Self>

Deprecated since 1.27.0

: Use str::from_utf8 instead: https://doc.rust-lang.org/nightly/std/str/struct.Utf8Error.html#examples

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

the semantics of a partial read/write of where errors happen is currently unclear and may change

Transforms this Read instance to an [Iterator] over [char]s.

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

Creates an adaptor which will chain this stream with another.

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

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

impl<P> Seek for ReadSlice<P> where     P: PosRead,

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

Seek to an offset, in bytes, in a stream. In this implementation, seeks are relative to the fixed start offset so a seek to SeekFrom::Start(0) is always the first byte of the slice.