hayro-syntax

A low-level library for reading PDF files.

This crate implements the Syntax chapter of the PDF reference, and therefore serves as a very good basis for building various abstractions on top of it, without having to reimplement the PDF parsing logic.

This crate does not provide more high-level functionality, such as parsing fonts or color spaces. Such functionality is out-of-scope for hayro-syntax, since this crate is supposed to be as light-weight and application-agnostic as possible.

Functionality-wise, this crate is therefore close to feature-complete. The main missing feature is support for encrypted and password-protected documents, as well as improved support for JPEG2000 documents. In addition to that, more low-level APIs might be added in the future.

Example

This short example shows you how to load a PDF file and iterate over the content streams of all pages.

use hayro_syntax::Pdf;
use std::path::PathBuf;
use std::sync::Arc;

// First load the data that constitutes the PDF file.
let data = std::fs::read(
    PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("../hayro/pdfs/text_with_rise.pdf"),
)
.unwrap();

// Then create a new PDF file from it.
//
// Here we are just unwrapping in case reading the file failed, but you
// might instead want to apply proper error handling.
let pdf = Pdf::new(Arc::new(data)).unwrap();

// First access all pages, and then iterate over the operators of each page's
// content stream and print them.
let pages = pdf.pages();
for page in pages.iter() {
    for op in page.typed_operations() {
        println!("{op:?}");
    }
}

Safety

There is one usage of unsafe, needed to implement caching using a self-referential struct. Other than that, there is no usage of unsafe, especially in any of the parser code.

Features

The supported features include:

• Parsing xref tables in all its possible formats, including xref streams.
• Best-effort attempt at repairing PDF files with broken xref tables.
• Parsing of all objects types (also in object streams).
• Parsing and evaluating PDF functions.
• Parsing and decoding PDF streams.
• Iterating over pages as well as their content streams in a typed or untyped fashion.
• The crate is very lightweight, especially in comparison to other PDF crates, assuming you don't enable the jpeg2000 feature (see further below for more information).

Limitations

• There are still a few features missing, for example, support for encrypted and password-protected PDFs. In addition to that, many properties (like page annotations) are currently not exposed.
• This crate is for read-only processing, you cannot directly use it to manipulate PDF files. If you need to do that, there are other crates in the Rust ecosystem that are suitable for this.

Cargo features

This crate has one feature, jpeg2000. PDF allows for the insertion of JPEG2000 images. However, unfortunately, JPEG2000 is a very complicated format. There exists a Rust jpeg2k crate that allows decoding such images. However, it is a relatively heavy dependency, has a lot of unsafe code (due to having been ported with c2rust), and also has a dependency on libc, meaning that you might be restricted in the targets you can build to. Because of this, I recommend not enabling this feature unless you absolutely need to be able to support such images.

License

This crate is available under the Apache 2.0 license.