@procwire/client

Child-side API for Procwire IPC.

Highlights

- Client - Fluent builder for registering handlers
- RequestContext - respond, ack, chunk, end, error
- Event emission to parent process
- Cancellation via ctx.aborted and ctx.onAbort()
- Async response methods - backpressure-safe
- ~2.5 GB/s throughput on named pipes

Installation

``bash
npm install @procwire/client
`

Requirements: Node.js >= 22

Dependencies: @procwire/protocol, @procwire/codecs

Quick Start

`typescript
import { Client } from "@procwire/client";

const client = new Client()
.handle("query", async (data, ctx) => {
const results = await search(data);
ctx.respond(results);
})
.handle("insert", async (data, ctx) => {
ctx.ack({ accepted: true });
await processInBackground(data);
})
.event("progress");

await client.start();

// Emit events to parent
client.emitEvent("progress", { percent: 50 });
`

API Reference

$3

Fluent builder for registering method handlers and events.

`typescript
const client = new Client(options?)
.handle(name, handler, definition?)
.event(name, definition?)
.start();
`

#### Constructor Options

`typescript
interface ClientOptions {
defaultCodec?: Codec; // Default codec for all methods/events
}
`

#### .handle(name, handler, definition?)

Register a method handler.

`typescript
client.handle(
"process",
async (data, ctx) => {
// Handle request and send response
ctx.respond(result);
},
{
response: "result", // "result" | "stream" | "ack" | "none"
codec: msgpackCodec, // Optional, defaults to msgpack
cancellable: true, // Support AbortSignal from parent
},
);
`

#### .event(name, definition?)

Register an event that can be emitted to parent.

`typescript
client.event("progress", { codec: msgpackCodec });
`

#### .start()

Start listening for requests from parent.

`typescript
await client.start();
// Client is now ready to receive requests
`

#### .emitEvent(name, data)

Emit an event to the parent process.

`typescript
client.emitEvent("progress", { percent: 75 });
`

$3

Passed to method handlers to send responses back to parent.

`typescript
interface RequestContext {
readonly requestId: number; // For correlation
readonly method: string; // Method being handled
readonly aborted: boolean; // Was request aborted?

onAbort(callback: () => void): void; // Abort callback

respond(data: unknown): Promise; // Full response
ack(data?: unknown): Promise; // Acknowledgment only
chunk(data: unknown): Promise; // Stream chunk
end(): Promise; // End stream
error(err: Error | string): Promise; // Error response
}
`

Important: All response methods are async to handle backpressure. Always await them.

$3

#### Single Response (result)

`typescript
client.handle(
"query",
async (data, ctx) => {
const result = await processQuery(data);
await ctx.respond(result);
},
{ response: "result" },
);
`

#### Streaming Response (stream)

`typescript
client.handle(
"generate",
async (data, ctx) => {
for (const item of generateItems(data)) {
await ctx.chunk(item);
}
await ctx.end();
},
{ response: "stream" },
);
`

#### Acknowledgment (ack)

`typescript
client.handle(
"enqueue",
async (data, ctx) => {
await ctx.ack({ queued: true, position: 42 });
// Continue processing after acknowledgment
await processInBackground(data);
},
{ response: "ack" },
);
`

#### Fire-and-Forget (none)

`typescript
client.handle(
"log",
(data, ctx) => {
logger.info(data);
// No response needed
},
{ response: "none" },
);
`

#### Error Response

`typescript
client.handle("validate", async (data, ctx) => {
try {
const result = validate(data);
await ctx.respond(result);
} catch (e) {
await ctx.error(e);
}
});
`

$3

Handle request cancellation from parent.

`typescript
client.handle(
"longTask",
async (data, ctx) => {
const resources = await acquireResources();

// Register cleanup on abort
ctx.onAbort(() => {
resources.release();
});

// Check abort status periodically
for (const item of items) {
if (ctx.aborted) {
return; // Stop processing
}
await ctx.chunk(process(item));
}

await ctx.end();
},
{ response: "stream", cancellable: true },
);
`

$3

`typescript
import { ProcwireClientError, ClientErrors } from "@procwire/client";

// Error factories
ClientErrors.methodNotFound("unknown"); // Unknown method called
ClientErrors.handlerError("process", err); // Handler threw error
ClientErrors.alreadyStarted(); // start() called twice
`

Architecture

`
┌─────────────────────────────────────────┐
│ Parent Process │
│ ┌───────────────────────────────────┐ │
│ │ Module (uses @procwire/core) │ │
│ │ - send(), stream(), onEvent() │ │
│ └───────────────┬───────────────────┘ │
└──────────────────┼──────────────────────┘
│
┌──────────────┴──────────────┐
│ Control: stdio (JSON-RPC) │
│ Data: named pipe (BINARY) │
└──────────────┬──────────────┘
│
┌──────────────────┼──────────────────────┐
│ Child Process │
│ ┌───────────────┴───────────────────┐ │
│ │ Client (uses @procwire/client) │ │
│ │ - handle(), event(), emitEvent() │ │
│ └───────────────────────────────────┘ │
└─────────────────────────────────────────┘
``

License

MIT