Struct tectonic_io_base::InputHandle

pub struct InputHandle { /* fields omitted */ }

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

Create a new InputHandle wrapping an underlying type that implements InputFeatures.

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

Create a new InputHandle in read-only mode.

pub fn name(&self) -> &OsStr

Get the name associated with this handle.

pub fn origin(&self) -> InputOrigin

Get the "origin" associated with this handle.

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

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

pub fn scan_remainder(&mut self) -> Result<()>

Read any remaining data in the file and incorporate them into the digest. This helps the rerun detection logic work correctly in the somewhat-unusual case that a file is read then written, but only part of the file is read, not the entire thing. This seems to happen with biblatex XML state files.

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

Consumes the object and returns the SHA256 sum of the content that was read. 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. Finally, no digest is returned if the file is marked read-only.

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

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

Get the size of the stream. Return TectonicIoError::NotSizeable if the operation is not well-defined for this stream.

pub fn get_unix_mtime(&mut self) -> Result<Option<i64>>

Get the modification time of this file as a Unix time. If that quantity is not meaningfully defined for this input, return Ok(None). This is what the default implementation does.

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

Try to seek within the stream. Return TectonicIoError::NotSeekable if the operation is not possible for this stream.

impl Read for InputHandle

pub 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.

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

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

pub 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.

pub 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.

pub 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.

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

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

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

Read the exact number of bytes required to fill buf.

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

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

pub fn bytes(self) -> Bytes<Self>

Transforms this Read instance to an Iterator over its bytes.

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

Creates an adaptor which will chain this stream with another.

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

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