Sidecar processes
Feature-gated behind sidecar. Spawn and manage helper child processes: their
stdout/stderr lines and exit are streamed to the frontend, and you can write
to stdin or kill them.
elyra = { version = "0.5", features = ["sidecar"] }
No extra crate is pulled in — the feature enables the needed tokio bits.
Frontend spawn is deny-by-default
An unrestricted spawn endpoint turns any script in the webview into arbitrary code execution, so the frontend may only spawn programs the app has named:
App::new()
.sidecar_allow("my-helper") // a bare name, or
.sidecar_allow("/opt/tools/encoder") // an exact path
.run()
A bare name also matches an absolute path ending in that name
("ffmpeg" allows /usr/local/bin/ffmpeg); an entry given as a path must match
exactly. Without an allowlist, sidecar.spawn(..) from the frontend rejects with
sidecar: no programs are allowed for frontend spawn.
Rust-side ctx.get::<Sidecar>().spawn(..) is not restricted — the policy
gates the untrusted caller (the webview), not your own code.
Frontend API
import { sidecar, onSidecar } from "@elyra/runtime";
const off = onSidecar((e) => {
if (e.kind === "data") console.log(`[${e.stream}] ${e.line}`);
if (e.kind === "exit") console.log("exited with", e.code);
});
const id = await sidecar.spawn("my-helper", ["--serve", "8080"]);
await sidecar.write(id, "input line\n");
await sidecar.kill(id);
Each event carries the sidecar id, a kind ("data" | "exit"), and for
output the stream ("stdout" | "stderr") + line, or for exit the code.
Rust API
Also available in the container as Sidecar:
use elyra::sidecar::Sidecar;
#[command]
async fn start_helper(ctx: Ctx) -> Result<u32> {
Ok(ctx.get::<Sidecar>().spawn("my-helper", &["--serve".into()])?)
}
Output is line-buffered (one line = one event). To ship a helper binary
alongside your app, place it next to the executable (see paths().exe in
system integration) and spawn it by absolute path.