Struct tectonic::io::InputHandle

pub struct InputHandle { /* private fields */ }

Input handles are basically Read objects with a few extras. We don’t require the standard io::Seek because we need to provide a dummy implementation for GZip streams, which we wouldn’t be allowed to do because both the trait and the target struct are outside of our crate.

An important role for the InputHandle struct is computing a cryptographic digest of the input file. The driver uses this information in order to figure out if the TeX engine needs rerunning. TeX makes our life more difficult, though, since it has somewhat funky file access patterns. LaTeX file opens work by opening a file and immediately closing it, which tests whether the file exists, and then by opening it again for real. Under the hood, XeTeX reads a couple of bytes from each file upon open to sniff its encoding. So we can’t just stream data from read() calls into the SHA2 computer, since we end up seeking and reading redundant data.

The current system maintains some internal state that, so far, helps us Do The Right Thing given all this. If there’s a seek on the file, we give up on our digest computation. But if there’s a seek back to the file beginning, we are open to the possibility of restarting the computation. But if nothing is ever read from the file, we once again give up on the computation. The ExecutionState code then has further pieces that track access to nonexistent files, which we treat as being equivalent to an existing empty file for these purposes.

Implementations

impl InputHandle

pub fn new<T: 'static + InputFeatures>(
    name: &OsStr,
    inner: T,
    origin: InputOrigin
) -> InputHandle

pub fn name(&self) -> &OsStr

pub fn origin(&self) -> InputOrigin

pub fn into_inner(self) -> Box<dyn InputFeatures>

Consumes the object and returns the underlying readable handle that it references.

pub fn into_name_digest(self) -> (OsString, Option<DigestData>)

Consumes the object and returns the SHA256 sum of the content that was written. No digest is returned if there was ever a seek on the input stream, since in that case the results will not be reliable. We also return None if the stream was never read, which is another common TeX access pattern: files are opened, immediately closed, and then opened again.

pub fn getc(&mut self) -> Result<u8>

Various piece of TeX want to use the libc ungetc() function a lot. It’s kind of gross, but happens often enough that we provide special support for it. Here’s getc() emulation that can return a previously ungetc()-ed character.

pub fn ungetc(&mut self, byte: u8) -> Result<()>

Here’s the ungetc() emulation.

Trait Implementations

impl InputFeatures for InputHandle

fn get_size(&mut self) -> Result<usize>

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

impl Read for InputHandle

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, Global>) -> 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 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)

Read the exact number of bytes required to fill cursor.

fn by_ref(&mut self) -> &mut Selfwhere
    Self: Sized,

Creates a “by reference” adaptor 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.