kkrpc

This project is created for building extension system for a Tauri app (https://github.com/kunkunsh/kunkun).

It can potentially be used in other types of apps, so I open sourced it as a standalone package.

A TypeScript-first RPC library that enables seamless bi-directional communication between processes. Call remote functions as if they were local, with full TypeScript type safety and autocompletion support.

• JSR Package
• NPM Package
• Documentation by JSR
• Typedoc Documentation

Excalidraw Diagrams

Features

• Cross-runtime compatibility: Works seamlessly across Node.js, Deno, Bun, browsers, and more
• Type-safe remote calls: Full TypeScript inference and IDE autocompletion support
• Bidirectional communication: Both endpoints can expose and call APIs simultaneously
• Property access: Remote property getters and setters with dot notation (await api.prop, api.prop = value)
• Enhanced error preservation: Complete error object preservation across RPC boundaries including stack traces, causes, and custom properties
• Multiple transport protocols: stdio, HTTP, WebSocket, postMessage, Chrome extensions
• Callback support: Remote functions can accept callback functions as parameters
• Nested object calls: Deep method chaining like api.math.operations.calculate()
• Automatic serialization: Intelligent detection between JSON and superjson formats
• Zero configuration: No schema files or code generation required

Supported Environments

• stdio: RPC over stdio between any combinations of Node.js, Deno, Bun processes
• web: RPC over postMessage API and message channel between browser main thread and web workers, or main thread and iframe
  • Web Worker API (web standard) is also supported in Deno and Bun, the main thread can call functions in worker and vice versa.
• http: RPC over HTTP like tRPC
  • supports any HTTP server (e.g. hono, bun, nodejs http, express, fastify, deno, etc.)
• WebSocket: RPC over WebSocket

The core of kkrpc design is in RPCChannel and IoInterface.

• RPCChannel is the bidirectional RPC channel
• LocalAPI is the APIs to be exposed to the other side of the channel
• RemoteAPI is the APIs exposed by the other side of the channel, and callable on the local side
• rpc.getAPI() returns an object that is RemoteAPI typed, and is callable on the local side like a normal local function call.
• IoInterface is the interface for implementing the IO for different environments. The implementations are called adapters.
  • For example, for a Node process to communicate with a Deno process, we need NodeIo and DenoIo adapters which implements IoInterface. They share the same stdio pipe (stdin/stdout).
  • In web, we have WorkerChildIO and WorkerParentIO adapters for web worker, IframeParentIO and IframeChildIO adapters for iframe.

In browser, import from kkrpc/browser instead of kkrpc, Deno adapter uses node:buffer which doesn't work in browser.

interface IoInterface {
	name: string
	read(): Promise<Buffer | Uint8Array | string | null> // Reads input
	write(data: string): Promise<void> // Writes output
}

class RPCChannel<
	LocalAPI extends Record<string, any>,
	RemoteAPI extends Record<string, any>,
	Io extends IoInterface = IoInterface
> {}
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Serialization

kkrpc supports two serialization formats for message transmission:

• json: Standard JSON serialization
• superjson: Enhanced JSON serialization with support for more data types like Date, Map, Set, BigInt, and Uint8Array (default since v0.2.0)

You can specify the serialization format when creating a new RPCChannel:

// Using default serialization (superjson)
const rpc = new RPCChannel(io, { expose: apiImplementation })

// Explicitly using superjson serialization (recommended for clarity)
const rpc = new RPCChannel(io, {
	expose: apiImplementation,
	serialization: { version: "superjson" }
})

// Using standard JSON serialization (for backward compatibility)
const rpc = new RPCChannel(io, {
	expose: apiImplementation,
	serialization: { version: "json" }
})
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For backward compatibility, the receiving side will automatically detect the serialization format so older clients can communicate with newer servers and vice versa.

Examples

Below are simple examples.

Stdio Example

import { NodeIo, RPCChannel } from "kkrpc"
import { apiMethods } from "./api.ts"

const stdio = new NodeIo(process.stdin, process.stdout)
const child = new RPCChannel(stdio, { expose: apiMethods })
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import { spawn } from "child_process"

const worker = spawn("bun", ["scripts/node-api.ts"])
const io = new NodeIo(worker.stdout, worker.stdin)
const parent = new RPCChannel<{}, API>(io)
const api = parent.getAPI()

expect(await api.add(1, 2)).toBe(3)
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Property Access Example

kkrpc supports direct property access and mutation across RPC boundaries:

// Define API with properties
interface API {
	add(a: number, b: number): Promise<number>
	counter: number
	settings: {
		theme: string
		notifications: {
			enabled: boolean
		}
	}
}

const api = rpc.getAPI<API>()

// Property getters (using await for remote access)
const currentCount = await api.counter
const theme = await api.settings.theme
const notificationsEnabled = await api.settings.notifications.enabled

// Property setters (direct assignment)
api.counter = 42
api.settings.theme = "dark"
api.settings.notifications.enabled = true

// Verify changes
console.log(await api.counter) // 42
console.log(await api.settings.theme) // "dark"
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Enhanced Error Preservation

kkrpc preserves complete error information across RPC boundaries:

// Custom error class
class DatabaseError extends Error {
	constructor(message: string, public code: number, public query: string) {
		super(message)
		this.name = 'DatabaseError'
	}
}

// API with error-throwing method
const apiImplementation = {
	async getUserById(id: string) {
		if (!id) {
			const error = new DatabaseError("Invalid user ID", 400, "SELECT * FROM users WHERE id = ?")
			error.timestamp = new Date().toISOString()
			error.requestId = generateRequestId()
			throw error
		}
		// ... normal logic
	}
}

// Error handling on client side
try {
	await api.getUserById("")
} catch (error) {
	// All error properties are preserved:
	console.log(error.name)      // "DatabaseError"
	console.log(error.message)   // "Invalid user ID"
	console.log(error.code)      // 400
	console.log(error.query)     // "SELECT * FROM users WHERE id = ?"
	console.log(error.stack)     // Full stack trace
	console.log(error.timestamp) // ISO timestamp
	console.log(error.requestId) // Request ID
}
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Web Worker Example

import { RPCChannel, WorkerChildIO, type DestroyableIoInterface } from "kkrpc"

const worker = new Worker(new URL("./scripts/worker.ts", import.meta.url).href, { type: "module" })
const io = new WorkerChildIO(worker)
const rpc = new RPCChannel<API, API, DestroyableIoInterface>(io, { expose: apiMethods })
const api = rpc.getAPI()

expect(await api.add(1, 2)).toBe(3)
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import { RPCChannel, WorkerParentIO, type DestroyableIoInterface } from "kkrpc"

const io: DestroyableIoInterface = new WorkerChildIO()
const rpc = new RPCChannel<API, API, DestroyableIoInterface>(io, { expose: apiMethods })
const api = rpc.getAPI()

const sum = await api.add(1, 2)
expect(sum).toBe(3)
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HTTP Example

Codesandbox: https://codesandbox.io/p/live/4a349334-0b04-4352-89f9-cf1955553ae7

api.ts

Define API type and implementation.

export type API = {
	echo: (message: string) => Promise<string>
	add: (a: number, b: number) => Promise<number>
}

export const api: API = {
	echo: (message) => {
		return Promise.resolve(message)
	},
	add: (a, b) => {
		return Promise.resolve(a + b)
	}
}
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server.ts

Server only requires a one-time setup, then it won't need to be touched again. All the API implementation is in api.ts.

import { HTTPServerIO, RPCChannel } from "kkrpc"
import { api, type API } from "./api"

const serverIO = new HTTPServerIO()
const serverRPC = new RPCChannel<API, API>(serverIO, { expose: api })

const server = Bun.serve({
	port: 3000,
	async fetch(req) {
		const url = new URL(req.url)
		if (url.pathname === "/rpc") {
			const res = await serverIO.handleRequest(await req.text())
			return new Response(res, {
				headers: { "Content-Type": "application/json" }
			})
		}
		return new Response("Not found", { status: 404 })
	}
})
console.log(`Start server on port: ${server.port}`)
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client.ts

import { HTTPClientIO, RPCChannel } from "kkrpc"
import { api, type API } from "./api"

const clientIO = new HTTPClientIO({
	url: "http://localhost:3000/rpc"
})
const clientRPC = new RPCChannel<{}, API>(clientIO, { expose: api })
const clientAPI = clientRPC.getAPI()

const echoResponse = await clientAPI.echo("hello")
console.log("echoResponse", echoResponse)

const sum = await clientAPI.add(2, 3)
console.log("Sum: ", sum)
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Chrome Extension Example

For Chrome extensions, use the dedicated ChromePortIO adapter for reliable, port-based communication.

background.ts

import { ChromePortIO, RPCChannel } from "kkrpc/chrome-extension";
import type { BackgroundAPI, ContentAPI } from "./types";

const backgroundAPI: BackgroundAPI = {
  async getExtensionVersion() {
    return chrome.runtime.getManifest().version;
  },
};

chrome.runtime.onConnect.addListener((port) => {
  if (port.name === "content-to-background") {
    const io = new ChromePortIO(port);
    const rpc = new RPCChannel(io, { expose: backgroundAPI });
    // Handle disconnect
    port.onDisconnect.addListener(() => io.destroy());
  }
});
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content.ts

import { ChromePortIO, RPCChannel } from "kkrpc/chrome-extension";
import type { BackgroundAPI, ContentAPI } from "./types";

const contentAPI: ContentAPI = {
  async getPageTitle() {
    return document.title;
  },
};

const port = chrome.runtime.connect({ name: "content-to-background" });
const io = new ChromePortIO(port);
const rpc = new RPCChannel<ContentAPI, BackgroundAPI>(io, { expose: contentAPI });

const backgroundAPI = rpc.getAPI();

// Example call
backgroundAPI.getExtensionVersion().then(version => {
  console.log("Extension version:", version);
});
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Chrome Extension Features:

• Port-based: Uses chrome.runtime.Port for stable, long-lived connections.
• Bidirectional: Both sides can expose and call APIs.
• Type-safe: Full TypeScript support for your APIs.
• Reliable: Handles connection lifecycle and cleanup.

Tauri Example

Call functions in bun/node/deno processes from Tauri app with JS/TS.

It allows you to call any JS/TS code in Deno/Bun/Node processes from Tauri app, just like using Electron.

Seamless integration with Tauri's official shell plugin and unlocked shellx plugin.

import { RPCChannel, TauriShellStdio } from "kkrpc/browser"
import { Child, Command } from "@tauri-apps/plugin-shell"

const localAPIImplementation = {
	add: (a: number, b: number) => Promise.resolve(a + b)
}

async function spawnCmd(runtime: "deno" | "bun" | "node") {
	let cmd: Command<string>
	let process = Child | null = null

	if (runtime === "deno") {
		cmd = Command.create("deno", ["run", "-A", scriptPath])
		process = await cmd.spawn()
	} else if (runtime === "bun") {
		cmd = Command.create("bun", [scriptPath])
		process = await cmd.spawn()
	} else if (runtime === "node") {
		cmd = Command.create("node", [scriptPath])
		process = await cmd.spawn()
	} else {
		throw new Error(`Invalid runtime: ${runtime}, pick either deno or bun`)
	}

	// monitor stdout/stderr/close/error for debugging and error handling
	cmd.stdout.on("data", (data) => {
		console.log("stdout", data)
	})
	cmd.stderr.on("data", (data) => {
		console.warn("stderr", data)
	})
	cmd.on("close", (code) => {
		console.log("close", code)
	})
	cmd.on("error", (err) => {
		console.error("error", err)
	})

	const stdio = new TauriShellStdio(cmd.stdout, process)
	const stdioRPC = new RPCChannel<typeof localAPIImplementation, RemoteAPI>(stdio, {
		expose: localAPIImplementation
	})

	const api = stdioRPC.getAPI();
	await api
		.add(1, 2)
		.then((result) => {
			console.log("result", result)
		})
		.catch((err) => {
			console.error(err)
		})

	process?.kill()
}
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I provided a sample tauri app in examples/tauri-demo.