https://github.com/ryanfowler/rfc9839-rs

Validation of RFC 9839 Unicode subsets in Rust.
https://github.com/ryanfowler/rfc9839-rs

Last synced: 22 days ago
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Validation of RFC 9839 Unicode subsets in Rust.

• Host: GitHub
• URL: https://github.com/ryanfowler/rfc9839-rs
• Owner: ryanfowler
• License: apache-2.0
• Created: 2025-08-23T15:30:28.000Z (8 months ago)
• Default Branch: main
• Last Pushed: 2025-09-09T23:10:45.000Z (8 months ago)
• Last Synced: 2025-12-29T17:43:35.529Z (4 months ago)
• Language: Rust
• Homepage:
• Size: 13.7 KB
• Stars: 1
• Watchers: 0
• Forks: 0
• Open Issues: 1
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

          
# rfc9839

[![Crates.io](https://img.shields.io/crates/v/rfc9839.svg)](https://crates.io/crates/rfc9839)

[![Docs.rs](https://docs.rs/rfc9839/badge.svg)](https://docs.rs/rfc9839)

[![License](https://img.shields.io/crates/l/rfc9839.svg)](#license)

Validation of [RFC 9839](https://www.rfc-editor.org/rfc/rfc9839) Unicode subsets in Rust.

RFC 9839 defines three nested subsets of Unicode characters for use in text protocols:

- **Unicode Scalars** – all code points except UTF-16 surrogates.

  *Every Rust `char` is already a scalar value; checks are included for completeness and for raw byte validation.*

- **XML Characters** – `{ TAB, LF, CR } ∪ [0x20–0xD7FF] ∪ [0xE000–0xFFFD] ∪ [0x10000–0x10FFFF]`.

  *This is the XML “Char” production with legacy controls and noncharacters excluded.*

- **Unicode Assignables** – “not problematic” characters: useful controls, printable ASCII (excluding DEL/C1),

  and all assigned scalars minus standardized noncharacters (…FFFE/FFFF in each plane and U+FDD0–FDEF).

---

## Features

- **Character-level APIs**: `is_unicode_scalar_char`, `is_xml_char`, `is_unicode_assignable_char`

- **String-level APIs**: `is_unicode_scalar`, `is_xml_chars`, `is_unicode_assignable`

- **Byte-level APIs**: `is_unicode_scalar_bytes`, `is_xml_chars_bytes`, `is_unicode_assignable_bytes`

- **ASCII fast-path**: tight loops for ASCII data, falling back to `chars()` only after the first non-ASCII byte

- **Zero allocations**, no lookup tables

## Example

```rust

use rfc9839::*;

// Scalars (always true for safe Rust strings)

assert!(is_unicode_scalar("hello 🌍"));

// XML Characters

assert!(is_xml_chars("ok\tline\n"));

assert!(!is_xml_chars("\u{0000}")); // NUL is disallowed

// Unicode Assignables

assert!(is_unicode_assignable("emoji 👍"));

assert!(!is_unicode_assignable("\u{007F}")); // DEL is excluded

```