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About

Oxidized rust re-implementation of readCon.

Reads and writes both .con (coordinate-only) and .convel (coordinates plus velocities) simulation configuration files used by eOn.

Features

CON and convel support: Parses both coordinate-only and velocity-augmented files. Velocity sections are auto-detected without relying on file extensions.
Lazy iteration: ConFrameIterator parses one frame at a time for memory-efficient trajectory processing.
Performance: Uses fast-float2 (Eisel-Lemire algorithm) for the f64 parsing hot path and memmap2 for large trajectory files.
Parallel parsing: Optional rayon-based parallel frame parsing behind the parallel feature gate.
Language bindings: Python (PyO3), Julia (ccall), C (cbindgen FFI), and C++ (RAII header-only wrapper), following the hourglass design from Metatensor.
Spec-v2 metadata helpers: Rust, Python, Julia, C, and C++ bindings all expose typed helpers for common JSON metadata keys like energy, frame_index, time, timestep, neb_bead, and neb_band, while still allowing raw JSON metadata when needed.
Spec-v2 validation: validate=true enforces finite numeric values, reserved metadata schema, physical header geometry, exact component labels, valid symbols, declared section presence, and matching per-atom identity columns.
Force and constraint fidelity: Writers preserve velocities, forces, original atom ids, and per-axis fixed masks across Rust, Python, Julia, C, and C++.
RPC serving: Optional Cap'n Proto RPC interface (rpc feature) for network-accessible parsing.

Install

Language	Install command
Rust	`cargo add readcon-core`
Python	`pip install readcon`
Julia	`julia --project=julia/ReadCon -e 'using Pkg; Pkg.instantiate()'`
C / C++ system	`cargo cinstall --release --prefix /usr/local` (installs `libreadcon_core.{so,a}`, `readcon-core.h`, `readcon-core.hpp`, and a pkg-config file)
C / C++ via meson subproject	drop the repository under `subprojects/readcon-core/` and link against the `readcon_core_dep` dependency

The C/C++ headers require a C99 (readcon-core.h) or C++17 (readcon-core.hpp, for std::optional and std::filesystem) compiler.

Tutorial

A copy-pasteable walkthrough that parses a multi-frame trajectory, inspects metadata, builds a new frame, and writes it back. Run it as-is.

cargo run --example rust_usage -- resources/test/tiny_multi_cuh2.con

The example above iterates lazily over every frame, prints atom counts plus the per-frame energy if present, and exits. Equivalent flows in the other bindings:

import readcon

# Read every frame; the iterator yields PyConFrame objects
for frame in readcon.iter_frames("resources/test/tiny_multi_cuh2.con"):
    print(frame.natms_per_type, frame.energy())  # energy() is None when absent

# Build and write a new frame
b = readcon.ConFrameBuilder(cell=[10.0, 10.0, 10.0], angles=[90.0, 90.0, 90.0])
b.set_energy(-42.5).add_atom("Cu", 0.0, 0.0, 0.0, 1, 63.546)
b.write("out.con")

using ReadCon
for frame in iter_frames("resources/test/tiny_multi_cuh2.con")
    println(frame.natms_per_type, " ", energy(frame))
end

#include <readcon-core.hpp>
#include <iostream>

int main() {
    readcon::ConFrameIterator it("resources/test/tiny_multi_cuh2.con");
    for (const auto &frame : it) {
        std::cout << frame.atoms().size() << " atoms";
        if (auto e = frame.energy_opt()) std::cout << " E=" << *e;
        std::cout << "\n";
    }
}

#include <readcon-core.h>
#include <stdio.h>

int main(void) {
    uintptr_t n = 0;
    RKRConFrame **frames = rkr_read_all_frames("resources/test/tiny_multi_cuh2.con", &n);
    for (uintptr_t i = 0; i < n; ++i) {
        printf("frame %zu energy=%f\n", i, rkr_frame_energy(frames[i]));
    }
    free_rkr_frame_array(frames, n);
}

Design Decisions

The library is designed with the following principles in mind:

Lazy Parsing: The ConFrameIterator allows for lazy parsing of frames, which can be more memory-efficient when dealing with large trajectory files.
Interoperability: The FFI layer makes the core parsing logic accessible from other programming languages, increasing the library's utility. Currently, a C header is auto-generated along with a hand-crafted C++ interface, following the hourglass design from Metatensor.

FFI Layer

A key challenge in designing an FFI is deciding how data is exposed to the C-compatible world. This library uses a hybrid approach to offer both safety and convenience:

Opaque Pointers (The Handle Pattern): The primary way to interact with frame data is through an opaque pointer, represented as RKRConFrame* in C. The C/C++ client holds this "handle" but cannot inspect its contents directly. Instead, it must call Rust functions to interact with the data (e.g., rkr_frame_get_header_line(frame_handle, ...)). This is the safest and most flexible pattern, as it completely hides Rust's internal data structures and memory layout, preventing ABI breakage if the Rust code is updated.
Transparent #[repr(C)] Structs (The Data Extraction Pattern): For convenience and performance in cases where only the core atomic data is needed, the library provides a function (rkr_frame_to_c_frame) to extract a "lossy" but transparent CFrame struct from an opaque handle. The C/C++ client can directly read the fields of this struct (e.g., my_c_frame->num_atoms). The client takes ownership of this extracted struct and is responsible for freeing its memory.

This hybrid model provides the best of both worlds: the safety and forward-compatibility of opaque handles for general use, and the performance of direct data access for the most common computational tasks.

Specification

See docs/orgmode/spec.org (or the published HTML build) for the full specification. A summary follows.

CON format

A 9-line header (comments, cell dimensions, cell angles, atom type/count/mass metadata)
Line 2 is reserved for spec-v2 JSON metadata
Per-type coordinate blocks (symbol, label, atom lines with x y z fixed atomID)
Optional spec-v2 sections and validate metadata for declared per-atom sections and strict validation
Multiple frames are concatenated directly with no separator

convel format

Same as CON, with an additional velocity section after each frame's coordinates:

A blank separator line
Per-type velocity blocks (symbol, label, atom lines with vx vy vz fixed atomID)

Why use this over readCon?

Speed, correctness, and multi-language bindings.

Citation

If you use readcon-core in academic work, please cite it via the metadata in CITATION.cff. The Zenodo DOI tracks the latest release.

License

MIT.

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readcon 0.13.1

Table of Contents

About

Features

Install

Tutorial

Design Decisions

FFI Layer

Specification

CON format

convel format

Why use this over readCon?

Citation

License

Project links

Key dates

1 maintainer

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SHA256	`5e5bc194c787f080fda6a9aff406622cb64fea9a2dbd3bf3e5b57c68b3bcf97e`
MD5	`bf02318c2a1d80d773db555f79905179`
BLAKE2b-256	`e8fbd06cf2c191ae4618d98567728ef2bff15674db913909b096233f6209fa4e`

Algorithm	Hash digest
SHA256	`edf57cc745cad95bdb8a5cef8f0090b1799598a9a03a4ce4ae67e7a381dedff7`
MD5	`4247091eff09dbcd58be01278a43cc71`
BLAKE2b-256	`12ffd6f80b5591f2295d13f6e76fa0a110e2d2fe028e85bc495369a608bbd1b8`