☀️ Helios

JIT at the edge, blazing like the sun.

Helios is a JavaScript runtime written in Rust for edge and serverless-style workloads. It provides a lock-free worker dispatcher, a shared bytecode cache, Hyper-based HTTP/1.1 + HTTP/2 serving, optional QUIC/HTTP/3 and WebTransport support, and a built-in benchmark harness.

The default build is self-contained: it embeds a pure-Rust Boa JavaScript engine, so it runs without any external JavaScript toolchain. An experimental SpiderMonkey/Ion backend is scaffolded behind a feature flag but is not yet production-ready.

This package (v1.2.0-rc1) contains a prebuilt Linux (x86_64) CLI binary plus the Rust crate source, so you can either run Helios immediately or build it yourself.

Quick start (prebuilt binary)

tar -xzf helios-v1.2.0-rc1-x86_64-unknown-linux-gnu.tar.gz
./bin/helios serve bench/helios-simple.js --port 8080

curl http://127.0.0.1:8080/

The response is produced by the JavaScript fetch handler in bench/helios-simple.js, so this exercises the full request path through the embedded engine.

Building from source

The rs/ directory contains the Helios Rust workspace (the helios crate) so this package can also be published to crates.io or built locally:

cd rs
cargo build --release -p helios
./target/release/helios serve ../bench/helios-simple.js --port 8080

Metadata

Helios is published on crates.io as vrillabs-helios.

cargo install vrillabs-helios

Running the above command will globally install the helios binary.

Install as library

Run the following Cargo command in your project directory:

cargo add vrillabs-helios

Or add the following line to your Cargo.toml:

vrillabs-helios = "1.2.0-rc1"

Full API documentation is available on docs.rs.

Current capabilities

Area	Current status
Worker dispatch	Requests fan out to bounded, lock-free per-worker queues with no global request-path mutex, and worker/runtime threads are best-effort pinned to CPUs on Linux.
Bytecode cache	Bytecode compiles once and is shared across workers as immutable, reference-counted entries.
JavaScript execution	Uses the embedded Boa engine by default; an experimental SpiderMonkey backend is scaffolded but not production-ready.
HTTP server	HTTP/1.1 and HTTP/2 over TCP via Hyper 1.x; supplying a TLS cert/key enables QUIC/HTTP/3. Static responses use vectored writes for larger bodies to avoid extra copies.
WebTransport	HTTP/3 CONNECT detection and dispatcher handoff are present; full bidirectional stream pumping into JavaScript is ongoing work.
Benchmarking	A built-in closed-loop load generator (helios bench) reports HDR-histogram latencies and supports JSON output.

CLI

helios serve <app.js|dir> [--script] [--ip 0.0.0.0] [--port 8080]
                         [--workers N] [--policy round-robin|least-loaded|power-of-two]
                         [--cert PATH --key PATH] [--alt-svc 'h3=":8443"; ma=86400']
                         [--shutdown-timeout 60] [--warmup-fetch N]
helios build <app.js|dir> [-o app.wasm] [--worker-wasm helios-worker.wasm]
                          [--target wasip2] [--no-opt]
helios bench <url> [-d 30] [--warmup 3] [-c 64] [-R 50000]
                   [--http auto|http1|http2|http3] [--json] [--body-file PATH]
helios exec  <script.js> [--script]

Notes:

• Directory entry points resolve in this order: index.js, main.js, then worker.js.
• HTTP/3 requires TLS because QUIC requires TLS 1.3.
• --warmup-fetch N (or HELIOS_FETCH_WARMUP=N) proactively invokes each worker's fetch handler N times before it accepts traffic, priming JIT-capable backends. It is opt-in and most useful with JIT-tiered backends.

Performance

Helios is benchmarked with its own built-in helios bench load generator against static and dynamic (JavaScript fetch-handler) workloads, covering worker dispatch, the bytecode cache, and the HTTP/1 response path.

License

Helios is licensed under the VRIL LABS Open Source License. See LICENSE or vril.li/license.

"WinterJS promised the sun. Helios delivers it."