Rustine

High-performance Gel syntax parser that transforms unstructured text into JSON, XML, or YAML. A complete Rust rewrite of Python Gelatin, usable as a native Python module, a Rust library, or a standalone CLI tool.

Why Rustine?

Gelatin has been a reliable tool for converting network device output and other semi-structured text into structured data. However, its core dependency — SimpleParse — has not been updated for Python 3.12+ and is no longer maintained. This made Gelatin incompatible with modern Python versions.

Rustine solves this by reimplementing the entire Gelatin engine in Rust:

• Drop-in replacement — same Gel grammar language, same output format
• 10–19× faster than Python Gelatin (depending on workload and platform)
• 3–4× less memory on large inputs
• Works on Python 3.9–3.13+ via PyO3 — no C extension dependency
• 100% feature parity with the original Python implementation

Quick Start

Python

pip install rustine

from Rustine import rustine

grammar = r"""
define nl /\r?\n/
define ws /\s+/

grammar input:
    match 'Name:' ws /[^\r\n,]+/ /(?:\r?\n|,) */:
        out.open('user')
        out.add_attribute('.', 'name', '$2')
    match /[\w ]+/ ':' ws /[^\r\n,]+/ /(?:\r?\n|,) */:
        out.add('$0', '$3')
    match nl:
        do.return()
"""

input_text = "Name: Alice\nAge: 30\nOffice: 1st Ave\n"
print(rustine.parse_to_json(grammar, input_text))

Rust

cargo add rustine --no-default-features

use rustine::exec::{execute, serialize_execution, RuntimeFormat};

let result = execute(grammar_source, input_text);
let json = serialize_execution(&result, RuntimeFormat::Json);

CLI

cargo install rustine --features cli

rgel -s syntax.gel -f json input.txt
rgel -s syntax.gel -f xml  input.txt
rgel -s syntax.gel -f yaml input.txt

Performance

Benchmarked on 20.9 MB real-world IOS XR configuration (263 grammars, 113 regex patterns, 899 757 output nodes):

See BENCHMARKS.md for full cross-platform results (Windows, Linux glibc, Linux jemalloc), serialization timings, and reproduction instructions.

Alternatives

Rustine's niche: a grammar-driven text→tree transformer with a concise DSL (.gel files), hierarchical output, and native performance. It sits between simple template extractors (textfsm) and full parser generators (nom/pest).

Feature Highlights

• Gel grammar language — match, imatch, when, skip, define, grammar inheritance
• Rich output actions — create, add, replace, add_attribute, open, enter, leave, set_root_name
• Trigger system — enqueue_before/after/on_add/on_leave (single-shot and persistent)
• Captures — positional ($1, $2) and named ($name) with interpolation in paths and values
• Three output formats — JSON, XML, YAML
• Streaming execution — feed chunks incrementally via StreamingRunner
• Structured errors — GelError with source spans (line, column, offset)
• Semantic validation — regex pre-validation, inheritance checks, undefined grammar/variable warnings
• Python bindings — PyO3 + maturin, installable via pip
• CLI tool — rgel binary for shell pipelines

Cargo Features (compile-time)

Features are selected at build time via --features and control which capabilities are compiled into the binary. See Getting Started → Cargo Features for the full table and usage examples.

Key features: cli, jemalloc (default in Linux wheels), mimalloc, mmap, parallel, python (default).

Documentation

License

Dual-licensed under MIT or Apache-2.0.