--- url: >- https://adk.nht.io/api/batteries/isolation/child_process/interfaces/IsolatedChildLike.md description: >- The minimal Node `ChildProcess`-shaped duck this transport drives. Structurally satisfied by BOTH: --- # Interface: IsolatedChildLike Defined in: [src/batteries/isolation/child\_process/transport.ts:102](https://github.com/NHTIO/ADK/blob/v1.20260713.1/src/src/batteries/isolation/child_process/transport.ts#L102) The minimal Node `ChildProcess`-shaped duck this transport drives. Structurally satisfied by BOTH: * the object returned by `node:child_process`'s own `fork()`, and * an `execa`≥9 subprocess spawned with `{ ipc: true }` — empirically verified: execa's `Subprocess` type is `Omit> & ExecaCustomSubprocess`, i.e. it keeps the classic Node `ChildProcess` EventEmitter surface (`.send()`, `.on('message'|'exit'|'error', ...)`, `.kill()`, `.connected`) alongside execa's own promise-based `sendMessage()`/`getEachMessage()` API. This transport only ever uses the classic EventEmitter surface, so an execa `{ ipc: true }` subprocess satisfies this duck WITHOUT any adapter. execa's channel, like node's own `fork()`, defaults to JSON-style serialization unless the subprocess is spawned with `serialization: 'advanced'` (execa forwards that option straight to the underlying `child_process.fork()` it uses internally for `ipc: true`) — the same "pin `advanced` for exotic-value fidelity" requirement documented on [ForkIsolatedOptions](../type-aliases/ForkIsolatedOptions.md) applies whether the child came from this module's own `fork()` call or from a caller-supplied [ChildResolver](../type-aliases/ChildResolver.md). ## Remarks A [ChildResolver](../type-aliases/ChildResolver.md) must NOT itself attach a `'message'` listener to the child it returns before handing it back to this transport (e.g. for logging). Node buffers a child's `message`/`ipc` events until the FIRST listener is attached, then flushes the whole buffer to that one listener exactly once — a resolver-side listener attached first (even just to log) permanently steals the buffered `ready` envelope from `connect()`'s own listener, which then waits out `readyTimeoutMs` for a `ready` that already came and went. execa's `Subprocess` additionally proxies raw child events through its own internal debounced `message` re-emitter (see execa's `lib/ipc/forward.js`), so this applies to execa subprocesses too — empirically confirmed by instrumenting a resolver with a diagnostic `subprocess.on('message', ...)` and observing the resulting connection hang. A [ChildResolver](../type-aliases/ChildResolver.md) that returns an execa `{ ipc: true }` subprocess should attach its own no-op `.catch(() => {})` to it before returning. execa's subprocess is ITSELF a promise (via `mergePromise`) that settles REJECTED on a non-zero exit or termination signal — including the ordinary `SIGTERM` this transport's `terminate()` sends on every `dispose()`/`recycle()`. Since this transport only ever drives the classic EventEmitter surface (never awaits/`.then()`s the child itself — see this module's `spawnChild` remarks for why an unguarded `await`/`return` of a thenable child is unsafe in the first place), nothing else ever attaches a rejection handler; without one, a routine `terminate()` reports as an unhandled promise rejection. ## Properties | Property | Type | Description | Defined in | | -------------------------------------------- | --------- | --------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `connected?` | `boolean` | Whether the IPC channel is currently open. Read once at connect time for a `send`-before-`connect` sanity check; not polled thereafter. | [src/batteries/isolation/child\_process/transport.ts:120](https://github.com/NHTIO/ADK/blob/v1.20260713.1/src/src/batteries/isolation/child_process/transport.ts#L120) | ## Methods ### kill() ```ts kill(signal?: number | Signals): boolean | void; ``` Defined in: [src/batteries/isolation/child\_process/transport.ts:117](https://github.com/NHTIO/ADK/blob/v1.20260713.1/src/src/batteries/isolation/child_process/transport.ts#L117) Send a termination signal to the child. #### Parameters | Parameter | Type | | --------- | --------------------- | | `signal?` | `number` | `Signals` | #### Returns `boolean` | `void` *** ### off()? ```ts optional off(event: string, fn: (...args: any[]) => void): unknown; ``` Defined in: [src/batteries/isolation/child\_process/transport.ts:113](https://github.com/NHTIO/ADK/blob/v1.20260713.1/src/src/batteries/isolation/child_process/transport.ts#L113) Unsubscribe, mirroring `.on`. Optional — some resolvers may return a duck without it; this transport degrades to leaking the listener rather than throwing (the process is short-lived and torn down on `terminate()`/`recycle()` regardless). #### Parameters | Parameter | Type | | --------- | ------------------------------ | | `event` | `string` | | `fn` | (...`args`: `any`\[]) => `void` | #### Returns `unknown` *** ### on() ```ts on(event: string, fn: (...args: any[]) => void): unknown; ``` Defined in: [src/batteries/isolation/child\_process/transport.ts:109](https://github.com/NHTIO/ADK/blob/v1.20260713.1/src/src/batteries/isolation/child_process/transport.ts#L109) Subscribe to a child lifecycle/IPC event (`'message'`, `'exit'`, `'error'`). Listener param typed `any[]` to structurally match node's own `ChildProcess#on` overload set (whose listener signatures are themselves `(...args: any[]) => void`). #### Parameters | Parameter | Type | | --------- | ------------------------------ | | `event` | `string` | | `fn` | (...`args`: `any`\[]) => `void` | #### Returns `unknown` *** ### removeListener()? ```ts optional removeListener(event: string, fn: (...args: any[]) => void): unknown; ``` Defined in: [src/batteries/isolation/child\_process/transport.ts:115](https://github.com/NHTIO/ADK/blob/v1.20260713.1/src/src/batteries/isolation/child_process/transport.ts#L115) Alias some ducks expose instead of/alongside `off`. #### Parameters | Parameter | Type | | --------- | ------------------------------ | | `event` | `string` | | `fn` | (...`args`: `any`\[]) => `void` | #### Returns `unknown` *** ### send()? ```ts optional send(msg: unknown): boolean | void; ``` Defined in: [src/batteries/isolation/child\_process/transport.ts:105](https://github.com/NHTIO/ADK/blob/v1.20260713.1/src/src/batteries/isolation/child_process/transport.ts#L105) Send a message across the IPC channel. Returns `false` (or void, depending on the implementation) when the channel is closed/backed-up; this transport does not currently act on that return value. #### Parameters | Parameter | Type | | --------- | --------- | | `msg` | `unknown` | #### Returns `boolean` | `void`