encoding_rs

encoding_rs aspires to become an implementation of the Encoding Standard that

1. Is written in Rust.
2. Is suitable for use in Gecko as a replacement of uconv. (I.e. supports decoding to UTF-16 and encoding from UTF-16.)
3. Is suitable for use in Rust code (both in Gecko and independently of Gecko). (I.e. supports decoding to UTF-8 and encoding from UTF-8 and provides an API compatible with at least the most common ways of using rust-encoding.)

You should not expect the above-stated aspiration to be fulfilled yet.

Licensing

Please see the file named COPYRIGHT.

API Documentation

Generated API documentation is available online.

Design

For design considerations, please see the associated technical proposal to rewrite uconv in Rust.

Performance goals

For decoding to UTF-16, the goal is to perform at least as well as Gecko's old uconv. For decoding to UTF-8, the goal is to perform at least as well as rust-encoding.

Encoding to UTF-8 should be fast. (UTF-8 to UTF-8 encode should be equivalent to memcpy and UTF-16 to UTF-8 should be fast.)

Speed is a non-goal when encoding to legacy encodings. Encoding to legacy encodings should not be optimized for speed at the expense of code size as long as form submission and URL parsing in Gecko don't become noticeably too slow in real-world use.

Relationship with rust-encoding

This code is being prototyped as a new project as opposed to patches to rust-encoding both to avoid breaking rust-encoding with in-progress exploration and to be able to see where the API design would go from scratch given the goals.

It is expected that encoding_rs will use code from rust-encoding.

Evaluation of whether it makes sense to propose portions of encodingrs to be adopted into rust-encoding will be best deferred until encodingrs is further along as a prototype.

Roadmap

• [x] Design the low-level API.
• [x] Provide Rust-only convenience features (some BOM sniffing variants still TODO).
• [x] Provide an stl/gsl-flavored C++ API.
• [x] Implement all decoders and encoders.
• [ ] Add unit tests for all decoders and encoders.
• [ ] Finish BOM sniffing variants in Rust-only convenience features.
• [ ] Document the API.
• [ ] Publish the crate on crates.io.
• [ ] Create a solution for measuring performance.
• [ ] Test the performance impact of omitting duplicate bound checks using unsafe.
• [ ] Accelerate ASCII conversions using SSE2 on x86.
• [ ] Accelerate ASCII conversions using ALU register-sized operations on non-x86 architectures (process an usize instead of u8 at a time).
• [ ] Use Björn Höhrmann's lookup table acceleration for UTF-8 as adapted to Rust in rust-encoding.
• [ ] Compress consecutive zeros in CJK indices.
• [ ] Make lookups by label or name use binary search that searches from the end of the label/name to the start.
• [ ] Provide an XPCOM/MFBT-flavored C++ API.
• [ ] Replace uconv with encoding_rs in Gecko.
• [ ] Implement the rust-encoding API in terms of encoding_rs.
• [ ] Investigate the use of NEON on newer ARM CPUs that have a lesser penalty on data flow from NEON to ALU registers.