BREP_script_core — a small, bounded JavaScript call on Boa

BREP_script_core runs one JavaScript file on the pure-Rust Boa engine, calls one global function with one JSON argument, and hands back the function's JSON result or a message a person can read. It is the interpreter behind the BREP PLM server's administrator hooks and the BREP CAD application's scripts, natively and in the browser (wasm32-unknown-unknown).

It is for a host that wants user-written rules — "what number does this part get", "may this revision be released" — without giving the script anything the host did not hand it. The crate depends on Boa and serde_json only: no file system, no network, no clock. Every binding that reaches outside the interpreter is installed by the host.

Example

use brep_script_core::{call, Failure};
use serde_json::json;

let source = r#"
    function onRelease(part) {
        console.log("checking " + part.number);
        if (!part.description) throw new Error("a released part needs a description");
        return { ok: true, revision: part.revision + 1 };
    }
"#;

// No host bindings beyond `console`: pass an `install` that adds nothing.
let no_bindings = |_: &mut _, _: &_| Ok(());
let input = json!({"number": "P-100", "revision": 1, "description": "Bracket"});
match call(source, "hooks.js", "onRelease", &input, &no_bindings) {
    Ok(done) => println!("{} (log: {:?})", done.value, done.logs),
    Err(Failure { message, logs }) => eprintln!("refused: {message} (log: {logs:?})"),
}

This prints {"ok":true,"revision":2} (log: ["checking P-100"]). Without a description the call returns Failure with the message a released part needs a description.

How it behaves

• A fresh interpreter per call. Each call builds a new Boa Context, evaluates the file, calls the function and drops the context: no state leaks from one call into the next, and a Context (which is not Send) never crosses a thread.
• Host bindings. install(&mut Context, &Logs) runs after console is defined and before the file is evaluated; add your own globals there. brep_script_core::boa_engine re-exports Boa so your bindings name the same engine version.
• Failures are sentences. A throw, a parse error, or a function the file does not define all return Failure { message, logs }; for throw new Error("x") and throw "x" the message is x.
• Bounded, honestly. Each loop may run at most LOOP_ITERATION_LIMIT (10,000,000) iterations and the call depth is at most RECURSION_LIMIT (512), so while (true) {} and runaway recursion throw instead of hanging. There is no wall-clock limit: Boa cannot pre-empt a running script, so many individually bounded loops can still run long, and a script blocked in a host function is bounded only by that function's own timeout.

Feature flags

None. On wasm32 the crate turns on Boa's js feature by itself (a getrandom backend and a browser clock), so a host never has to.

Licence

The Autodrop3d licence in LICENSE.md, shipped in the crate (license-file in the manifest). It is not an SPDX licence: read it before you modify or redistribute the crate.