libhermes-sys

libhermes-sys

Warning

This crate currently only supports Linux and macOS. Adding Windows support should be trivial.

Low-level Rust FFI bindings for the Hermes JavaScript engine.

Provides flat extern "C" functions wrapping the Hermes JSI C++ API (rusty_v8 style). Pointer types (String, Object, Array, etc.) are represented as opaque *mut c_void handles that must be explicitly released.

For a safe, high-level API, see rusty_hermes.

Example

use libhermes_sys::*;

unsafe {
    let rt = hermes__Runtime__New();

    let script = b"1 + 2";
    let url = b"test.js";

    let result = hermes__Runtime__EvaluateJavaScript(
        rt,
        script.as_ptr(),
        script.len(),
        url.as_ptr() as *const i8,
        url.len(),
    );

    assert_eq!(result.kind, HermesValueKind_Number);
    assert_eq!(result.data.number, 3.0);

    hermes__Runtime__Delete(rt);
}

API surface

• Runtime — create (default/custom config), delete, evaluate JS, evaluate with source map, drain microtasks, queue microtask, get global object, parse JSON, description, inspectable, register/unregister for profiling, load segment, reset timezone cache
• RuntimeConfig — eval, Proxy, Intl, microtask queue, generators, block scoping, HermesInternal, max registers, JIT (enable/force/threshold/memory limit), async generators, bytecode warmup percent, randomize memory layout
• PreparedJavaScript — prepare, evaluate, delete
• Scope — push/pop handle scopes
• String — create from UTF-8/ASCII, convert to UTF-8, equality, unique ID, release
• PropNameID — create from string/UTF-8/ASCII/symbol, convert to UTF-8, equality, unique ID, release
• Object — create, get/set/has/delete property (string, PropNameID, and Value keys), property names, type checks, instanceof, external memory pressure, NativeState (has/get/set), HostObject (create/get/is), prototype (create/get/set), unique ID, release
• Array — create, size, get/set by index, release
• ArrayBuffer — create, size, data pointer
• Function — call (with/without this), call as constructor, create from host function, is host function, release
• Value — release, strict equality, to string, clone, unique ID
• Symbol — to string, equality, unique ID, release
• BigInt — create from i64/u64, type checks, truncate to u64, get i64, to string, equality, unique ID, release
• WeakObject — create, lock, release
• Hermes-specific — bytecode check/version/sanity/prefetch/epilogue, time limits (watch/unwatch/trigger), sampling profiler (enable/disable/dump), code coverage profiler (enable/disable/query), fatal handler, unique IDs for all pointer types

Installation

Install the required build dependencies:

Ubuntu

apt install cmake git ninja-build libicu-dev python zip libreadline-dev

Arch

pacman -S cmake git ninja icu python zip readline

macOS via Homebrew

brew install cmake git ninja

Add to your Cargo.toml:

libhermes-sys = { git = "https://github.com/rust-hermes/rusty_hermes", branch = "main" }