Trait file_offset::FileExt

pub trait FileExt {
    fn read_offset(&self, buf: &mut [u8], offset: u64) -> Result<usize>;
    fn write_offset(&self, buf: &[u8], offset: u64) -> Result<usize>;
}

This trait provides the extension methods for reading and writing files at specified offsets.

Note the difference between Windows and Unix behavior listed in the "Platform-specific behavior" sections.

Required Methods

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

Reads a number of bytes, starting at a given file offset.

Returns the number of bytes read.

The offset is relative to the start of the file and thus independent of the current cursor. Note that similarly to File::read, returning with a short read is not an error. Additionally, read errors that are of ErrorKind::Interrupted are transient and the read call should usually be retried.

Platform-specific behavior

This function delegates to std::os::unix::fs::FileExt::read_at and thus the pread64 function on Unix and to std::os::windows::fs::FileExt::seek_read and hence to a ReadFile function call using the lpOverlapped parameter on Windows.

The actions performed by these functions are not identical. In particular, the Windows version of this function moves the file cursor, whereas the Unix version does not.

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

Writes a number of bytes, starting at a given file offset.

Returns the number of bytes written.

The offset is relative to the start of the file and thus independent of the current cursor. Note that similarly to File::write, returning with a short write is not an error. Additionally, write errors that are of ErrorKind::Interrupted are transient and the write call should usually be retried.

Platform-specific behavior

This function delegates to std::os::unix::fs::FileExt::write_at and thus the pwrite64 function on Unix and to std::os::windows::fs::FileExt::seek_write and hence to a WriteFile function call using the lpOverlapped parameter on Windows.

The actions performed by these functions are not identical. In particular, the Windows version of this function moves the file cursor, whereas the Unix version does not.

Implementors

• impl FileExt for File