stdio Bus – Worker Registry

Worker implementations for stdio Bus kernel - a high-performance message routing daemon for agent protocols.

Features:

• Full ACP (Agent Client Protocol) implementation
• MCP (Model Context Protocol) server integration
• Protocol bridges (MCP ↔ ACP)
• TypeScript support with full type definitions
• High-performance NDJSON protocol
• Docker-ready

Installation

npm install @stdiobus/workers-registry

Requirements:

• Node.js ≥20.0.0
• stdio Bus kernel (Docker or binary)

Keywords: stdiobus, protocol, acp, mcp, agent, transport, json-rpc, stdio-bus, worker

Overview

stdio Bus kernel provides the core protocol and message routing infrastructure. This package contains the worker implementations that run as child processes of stdio Bus kernel, handling various agent protocols and use cases.

Architecture

graph TB
    Client[Client Application] -->|TCP/Unix Socket| Kernel[stdio Bus kernel]
    Kernel -->|NDJSON stdin/stdout| ACP[ACP Worker]
    Kernel -->|NDJSON stdin/stdout| Registry[ACP Registry Worker – acp-registry]
    Kernel -->|NDJSON stdin/stdout| Echo[Echo Worker]
    Kernel -->|NDJSON stdin/stdout| Proxy[MCP-to-ACP Proxy]
    
    Registry -->|Spawns| Claude[Claude Agent]
    Registry -->|Spawns| Goose[Goose Agent]
    Registry -->|Spawns| Cline[Cline Agent]
    Registry -->|Spawns| Other[Other ACP Agents]
    
    ACP -->|Connects to| MCP[MCP Servers]
    
    IDE[IDE] -->|MCP Protocol| Proxy
    Proxy -->|ACP Protocol| Kernel
    
    style Kernel fill:#4a90e2,stroke:#2e5c8a,stroke-width:3px,color:#fff
    style Registry fill:#50c878,stroke:#2d7a4a,stroke-width:2px,color:#fff
    style ACP fill:#9b59b6,stroke:#6c3483,stroke-width:2px,color:#fff
    style Proxy fill:#e67e22,stroke:#a04000,stroke-width:2px,color:#fff

Prerequisites

• stdio Bus kernel - available via Docker or build from source
• Node.js 20.0.0 or later (for building workers)

Workers

| Worker | Description | Protocol | Command | |--------|-------------|----------|---------| | acp-registry | Registry Launcher worker that routes to ACP Registry agents (requires api-keys.json) | ACP | node ./node_modules/@stdiobus/workers-registry/launch acp-registry | | acp-worker | Full ACP protocol implementation (standalone agent; does not route to ACP Registry) | ACP | node ./node_modules/@stdiobus/workers-registry/launch acp-worker | | registry-launcher | Registry Launcher implementation module used by acp-registry (not a launch target) | ACP | Use acp-registry | | mcp-to-acp-proxy | Bridges MCP clients (like IDEs) to ACP agents | MCP → ACP | node ./node_modules/@stdiobus/workers-registry/launch mcp-to-acp-proxy | | echo-worker | Simple echo worker for testing NDJSON protocol | NDJSON | node ./node_modules/@stdiobus/workers-registry/launch echo-worker | | mcp-echo-server | MCP server example for testing | MCP | node ./node_modules/@stdiobus/workers-registry/launch mcp-echo-server |

Note: The universal launcher is @stdiobus/workers-registry/launch. In this repo, use node ./launch/index.js <worker-name> after npm run build.

Package API

Module Imports

// Import ACP worker (default export)
import worker from '@stdiobus/workers-registry';

// Import specific workers
import acpWorker from '@stdiobus/workers-registry/workers/acp-worker';
import echoWorker from '@stdiobus/workers-registry/workers/echo-worker';
import mcpEchoServer from '@stdiobus/workers-registry/workers/mcp-echo-server';
import mcpToAcpProxy from '@stdiobus/workers-registry/workers/mcp-to-acp-proxy';

// Import workers metadata
import { workers } from '@stdiobus/workers-registry/workers';
console.log(workers['acp-worker'].entrypoint);

Note: acp-registry is a worker runtime launched via @stdiobus/workers-registry/launch and is not exported as a module.

TypeScript Support

Full TypeScript definitions are included:

import type { ACPAgent } from '@stdiobus/workers-registry/workers/acp-worker';
import type { MCPServer } from '@stdiobus/workers-registry/workers/mcp-echo-server';

Quick Start

1. Install Package

npm install @stdiobus/workers-registry

2. Get stdio Bus kernel

Option A: Using Docker (recommended)

docker pull stdiobus/stdiobus:latest

Option B: Build from source

See stdio Bus kernel repository for build instructions.

3. Run with ACP Registry (recommended for real agents)

Create config.json:

{
  "pools": [
    {
      "id": "acp-registry",
      "command": "npx",
      "args": [
        "@stdiobus/workers-registry",
        "acp-registry"
      ],
      "instances": 1
    }
  ]
}

Important: Place api-keys.json next to your stdio Bus config (working directory), or pass a custom config file (third arg to launch acp-registry) with an absolute apiKeysPath. In this repo, the default file is workers-registry/acp-registry/acp-registry-config.json. Use the same Docker/binary commands below (they run config.json), and ensure api-keys.json is mounted into the container when using Docker.

4. Run with ACP Worker

Note: acp-worker is a standalone ACP agent for SDK/protocol testing. It does not route to the ACP Registry. Use acp-registry when you need real registry agents.

Create config.json:

{
  "pools": [
    {
      "id": "acp-worker",
      "command": "npx",
      "args": [
        "@stdiobus/workers-registry",
        "acp-worker"
      ],
      "instances": 1
    }
  ]
}

Run with Docker:

docker run -p 9000:9000 \
  -v $(pwd):/stdiobus:ro \
  -v $(pwd)/config.json:/config.json:ro \
  stdiobus/stdiobus:latest \
  --config /config.json --tcp 0.0.0.0:9000

Or with binary:

./stdio_bus --config config.json --tcp 0.0.0.0:9000

5. Test Connection

# ACP worker (standalone)
echo '{"jsonrpc":"2.0","id":"1","method":"initialize","params":{"clientInfo":{"name":"test","version":"1.0"}}}' | nc localhost 9000

# ACP Registry worker (route to a registry agent)
echo '{"jsonrpc":"2.0","id":"1","method":"initialize","params":{"agentId":"claude-acp","clientInfo":{"name":"test","version":"1.0"}}}' | nc localhost 9000

Usage Examples

Using the Universal Launcher

The simplest way to run any worker:

# Run any worker by name (package install)
node ./node_modules/@stdiobus/workers-registry/launch <worker-name>

# Run any worker by name (this repo, after build)
node ./launch/index.js <worker-name>

# Available workers:
# - acp-registry
# - acp-worker
# - echo-worker
# - mcp-echo-server
# - mcp-to-acp-proxy

# Example: Run echo worker for testing
node ./node_modules/@stdiobus/workers-registry/launch echo-worker

Using in stdio Bus Configuration

Basic ACP Worker:

{
  "pools": [{
    "id": "acp-worker",
    "command": "npx",
    "args": [
      "@stdiobus/workers-registry",
      "acp-worker"
    ],
    "instances": 1
  }]
}

ACP Registry Worker with API Keys:

{
  "pools": [
    {
      "id": "acp-registry",
      "command": "npx",
      "args": [
        "@stdiobus/workers-registry",
        "acp-registry"
      ],
      "instances": 1
    }
  ]
}

Note: acp-registry reads api-keys.json via its config. The default apiKeysPath is ./api-keys.json. You can pass a custom config file as the third arg to launch acp-registry.

Multiple Workers:

{
  "pools": [
    {
      "id": "acp-worker",
      "command": "npx",
      "args": [
        "@stdiobus/workers-registry",
        "acp-worker"
      ],
      "instances": 2
    },
    {
      "id": "echo-worker",
      "command": "npx",
      "args": [
        "@stdiobus/workers-registry",
        "echo-worker"
      ],
      "instances": 1
    }
  ]
}

Using with Kiro IDE (MCP Client)

Configure MCP-to-ACP Proxy in Kiro's MCP settings:

{
  "mcpServers": {
    "stdio-bus-acp": {
      "command": "npx",
      "args": [
        "@stdiobus/workers-registry",
        "mcp-to-acp-proxy"
      ],
      "env": {
        "ACP_HOST": "localhost",
        "ACP_PORT": "9000",
        "AGENT_ID": "claude-acp"
      }
    }
  }
}

Note: Run acp-registry on the stdio Bus side so AGENT_ID resolves to real ACP Registry agents. acp-worker is a standalone agent and will not route to the registry.

Worker Documentation

ACP Worker

Full implementation of the Agent Client Protocol using the official @agentclientprotocol/sdk.

Location: workers-registry/acp-worker/

Features:

• Complete ACP protocol support (initialize, session management, prompts)
• MCP server integration for tool execution
• Session-based routing
• Graceful shutdown handling

Build:

cd workers-registry/acp-worker
npm install
npm run build

Run with stdio Bus:

Using Docker:

docker run \
  --name stdiobus-acp \
  -p 9000:9000 \
  -v $(pwd):/stdiobus:ro \
  -v $(pwd)/workers-registry/acp-worker/acp-worker-config.json:/config.json:ro \
  stdiobus/stdiobus:latest \
  --config /config.json --tcp 0.0.0.0:9000

Using binary:

./stdio_bus --config workers-registry/acp-worker/acp-worker-config.json --tcp 0.0.0.0:9000

Configuration: See workers-registry/acp-worker/src/ for implementation details.

ACP Registry Worker (acp-registry)

Routes messages to any agent in the ACP Registry.

Location (worker entrypoint): workers-registry/acp-registry/

Implementation: workers-registry/acp-worker/src/registry-launcher/

Features:

• Automatic agent discovery from ACP Registry
• Dynamic agent process management
• API key injection from configuration
• Session affinity routing

Available Agents:

• claude-acp - Claude Agent
• goose - Goose
• cline - Cline
• github-copilot - GitHub Copilot
• And many more from the registry

Configuration:

{
  "pools": [
    {
      "id": "acp-registry",
      "command": "npx",
      "args": [
        "@stdiobus/workers-registry",
        "acp-registry"
      ],
      "instances": 1
    }
  ]
}

Note: acp-registry uses its default config when no path is provided. You can pass a custom config file as the third arg to launch acp-registry. The default file in this repo is workers-registry/acp-registry/acp-registry-config.json, which expects api-keys.json at ./api-keys.json unless you override apiKeysPath.

Run:

Using Docker:

docker run \
  --name stdiobus-registry \
  -p 9000:9000 \
  -v $(pwd):/stdiobus:ro \
  -v $(pwd)/workers-registry/acp-registry/acp-registry-config.json:/config.json:ro \
  -v $(pwd)/api-keys.json:/api-keys.json:ro \
  stdiobus/stdiobus:latest \
  --config /config.json --tcp 0.0.0.0:9000

Using binary:

./stdio_bus --config workers-registry/acp-registry/acp-registry-config.json --tcp 0.0.0.0:9000

MCP-to-ACP Proxy

Bridges MCP clients (like IDE) to ACP agents through stdio Bus.

Location: workers-registry/mcp-to-acp-proxy/

Architecture:

IDE (MCP Client) → MCP-to-ACP Proxy → stdio Bus → ACP Registry Worker (acp-registry) → ACP Agent

Configuration for IDE:

{
  "mcpServers": {
    "stdio-bus-acp": {
      "command": "npx",
      "args": [
        "@stdiobus/workers-registry",
        "mcp-to-acp-proxy"
      ],
      "env": {
        "ACP_HOST": "0.0.0.0",
        "ACP_PORT": "9000",
        "AGENT_ID": "claude-acp"
      }
    }
  }
}

Documentation: See workers-registry/mcp-to-acp-proxy/README.md

Echo Worker

Simple reference implementation demonstrating the NDJSON worker protocol.

Location: workers-registry/echo-worker/

Purpose:

• Testing stdio Bus kernel functionality
• Reference implementation for custom workers
• Protocol documentation through code

Run standalone:

echo '{"jsonrpc":"2.0","id":"1","method":"test","params":{"foo":"bar"}}' | node workers-registry/echo-worker/echo-worker.js

Run with stdio Bus:

Using Docker:

docker run \
  --name stdiobus-echo \
  -p 9000:9000 \
  -v $(pwd):/stdiobus:ro \
  -v $(pwd)/workers-registry/echo-worker/echo-worker-config.json:/config.json:ro \
  stdiobus/stdiobus:latest \
  --config /config.json --tcp 0.0.0.0:9000

Using binary:

./stdio_bus --config workers-registry/echo-worker/echo-worker-config.json --tcp 0.0.0.0:9000

MCP Echo Server

TypeScript MCP server example for testing MCP integration.

Location: workers-registry/mcp-echo-server/

Tools provided:

• echo - Echoes input text
• reverse - Reverses input text
• uppercase - Converts to uppercase
• delay - Echoes after a delay (for testing cancellation)
• error - Always returns an error (for testing error handling)

Build:

cd workers-registry/mcp-echo-server
npm install
npm run build

Run:

node workers-registry/mcp-echo-server/dist/index.js

stdio Bus Configuration

stdio Bus kernel is configured via JSON files. This repository includes example configurations for each worker.

Configuration File Structure

{
  "pools": [
    {
      "id": "worker-id",
      "command": "/path/to/executable",
      "args": ["arg1", "arg2"],
      "instances": 1
    }
  ],
  "limits": {
    "max_input_buffer": 1048576,
    "max_output_queue": 4194304,
    "max_restarts": 5,
    "restart_window_sec": 60,
    "drain_timeout_sec": 30,
    "backpressure_timeout_sec": 60
  }
}

Pool Configuration

| Field | Type | Required | Description | |-------|------|----------|-------------| | id | string | Yes | Unique identifier for this worker pool | | command | string | Yes | Path to the executable | | args | string[] | No | Command-line arguments | | instances | number | Yes | Number of worker instances (≥ 1) |

Limits Configuration

| Field | Type | Default | Description | |-------|------|---------|-------------| | max_input_buffer | number | 1048576 (1 MB) | Maximum input buffer size per connection | | max_output_queue | number | 4194304 (4 MB) | Maximum output queue size per connection | | max_restarts | number | 5 | Maximum worker restarts within restart window | | restart_window_sec | number | 60 | Time window for counting restarts | | drain_timeout_sec | number | 30 | Timeout for graceful shutdown | | backpressure_timeout_sec | number | 60 | Timeout before closing connection when queue is full |

Example Configurations

Minimal Configuration:

{
  "pools": [{
    "id": "echo-worker",
    "command": "npx",
    "args": [
      "@stdiobus/workers-registry",
      "echo-worker"
    ],
    "instances": 1
  }]
}

High-Throughput Configuration:

{
  "pools": [
    {
      "id": "acp-worker",
      "command": "npx",
      "args": [
        "@stdiobus/workers-registry",
        "acp-worker"
      ],
      "instances": 4
    }
  ],
  "limits": {
    "max_input_buffer": 4194304,
    "max_output_queue": 16777216,
    "backpressure_timeout_sec": 120
  }
}

Multiple Worker Pools:

{
  "pools": [
    {
      "id": "acp-worker",
      "command": "npx",
      "args": [
        "@stdiobus/workers-registry",
        "acp-worker"
      ],
      "instances": 2
    },
    {
      "id": "echo-worker",
      "command": "npx",
      "args": [
        "@stdiobus/workers-registry",
        "echo-worker"
      ],
      "instances": 1
    }
  ]
}

NDJSON Protocol

Workers communicate with stdio Bus kernel via stdin/stdout using NDJSON (Newline-Delimited JSON).

Protocol Rules

1. Input (stdin): stdio Bus sends JSON-RPC messages, one per line
2. Output (stdout): Workers write JSON-RPC responses, one per line
3. Errors (stderr): All logging and debug output goes to stderr
4. Never write non-JSON to stdout - it will break the protocol

Message Types

Request (requires response):

{"jsonrpc":"2.0","id":"1","method":"test","params":{"foo":"bar"}}

Response:

{"jsonrpc":"2.0","id":"1","result":{"status":"ok"}}

Notification (no response):

{"jsonrpc":"2.0","method":"notify","params":{"event":"started"}}

Session Affinity

Messages with the same sessionId are routed to the same worker instance:

{"jsonrpc":"2.0","id":"1","method":"test","sessionId":"sess-123","params":{}}

Workers must preserve sessionId in responses for proper routing.

Graceful Shutdown

Workers must handle SIGTERM for graceful shutdown:

1. Stop accepting new messages
2. Complete in-flight processing
3. Exit with code 0

stdio Bus sends SIGTERM during shutdown or worker restarts.

Testing

Unit Tests

# Run all tests
npm test

# Run specific test suites
npm run test:unit
npm run test:integration
npm run test:property

Manual Testing

Test echo worker:

# Start stdio Bus with Docker
docker run \
  --name stdiobus-test \
  -p 9000:9000 \
  -v $(pwd):/stdiobus:ro \
  -v $(pwd)/workers-registry/echo-worker/echo-worker-config.json:/config.json:ro \
  stdiobus/stdiobus:latest \
  --config /config.json --tcp 0.0.0.0:9000

# Send test message
echo '{"jsonrpc":"2.0","id":"1","method":"echo","params":{"test":true}}' | nc localhost 9000

# Cleanup
docker stop stdiobus-test && docker rm stdiobus-test

Test ACP worker:

# Start stdio Bus with ACP worker
docker run \
  --name stdiobus-acp-test \
  -p 9000:9000 \
  -v $(pwd):/stdiobus:ro \
  -v $(pwd)/workers-registry/acp-worker/acp-worker-config.json:/config.json:ro \
  stdiobus/stdiobus:latest \
  --config /config.json --tcp 0.0.0.0:9000

# Send initialize request
echo '{"jsonrpc":"2.0","id":"1","method":"initialize","params":{"clientInfo":{"name":"test","version":"1.0"}}}' | nc localhost 9000

# Cleanup
docker stop stdiobus-acp-test && docker rm stdiobus-acp-test

Test ACP Registry Worker – acp-registry:

# Start stdio Bus with ACP Registry worker
docker run \
  --name stdiobus-registry-test \
  -p 9000:9000 \
  -v $(pwd):/stdiobus:ro \
  -v $(pwd)/workers-registry/acp-registry/acp-registry-config.json:/config.json:ro \
  -v $(pwd)/api-keys.json:/api-keys.json:ro \
  stdiobus/stdiobus:latest \
  --config /config.json --tcp 0.0.0.0:9000

# Send message with agentId
echo '{"jsonrpc":"2.0","id":"1","method":"initialize","params":{"agentId":"claude-acp","clientInfo":{"name":"test"}}}' | nc localhost 9000

# Cleanup
docker stop stdiobus-registry-test && docker rm stdiobus-registry-test

Development

Creating a Custom Worker

1. Workers must read NDJSON from stdin and write NDJSON to stdout
2. All logging goes to stderr
3. Handle SIGTERM for graceful shutdown
4. Preserve sessionId in responses when present in requests

Minimal worker template (Node.js):

#!/usr/bin/env node
import readline from 'readline';

const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout,
  terminal: false
});

rl.on('line', (line) => {
  try {
    const msg = JSON.parse(line);
    
    if (msg.id !== undefined) {
      // Request - send response
      const response = {
        jsonrpc: '2.0',
        id: msg.id,
        result: { /* your result */ }
      };
      
      if (msg.sessionId) {
        response.sessionId = msg.sessionId;
      }
      
      console.log(JSON.stringify(response));
    }
  } catch (err) {
    console.error('Parse error:', err.message);
  }
});

process.on('SIGTERM', () => {
  console.error('Shutting down...');
  rl.close();
});

rl.on('close', () => process.exit(0));

Project Structure

workers-registry/
├── acp-worker/              # Full ACP protocol implementation
│   ├── src/
│   │   ├── agent.ts         # ACP Agent implementation
│   │   ├── index.ts         # Main entry point
│   │   ├── mcp/             # MCP server integration
│   │   ├── session/         # Session management
│   │   └── registry-launcher/  # Registry Launcher implementation
│   └── tests/               # Test suites
├── acp-registry/            # ACP Registry worker entrypoint + configs
├── echo-worker/             # Simple echo worker example
├── mcp-echo-server/         # MCP server example
└── mcp-to-acp-proxy/        # MCP-to-ACP protocol bridge

API Reference

Package Exports

The package provides the following exports:

// Default export - ACP Worker
import worker from '@stdiobus/workers-registry';

// Named exports for specific workers
import { 
  acpWorker,
  echoWorker,
  mcpEchoServer,
  mcpToAcpProxy,
  workers  // Metadata object
} from '@stdiobus/workers-registry/workers';

Environment Variables

MCP-to-ACP Proxy:

• ACP_HOST - stdio Bus host (default: localhost)
• ACP_PORT - stdio Bus port (default: 9000)
• AGENT_ID - Target agent ID (e.g., claude-acp)

Versioning

This package follows Semantic Versioning:

• MAJOR version for incompatible API changes
• MINOR version for backwards-compatible functionality additions
• PATCH version for backwards-compatible bug fixes

Current version: 0.1.0 (pre-release)

Troubleshooting

Installation Issues

Node.js version mismatch:

node --version  # Must be ≥20.0.0
nvm install 20  # If using nvm

Permission errors:

npm install -g @stdiobus/workers-registry  # Global install (may need sudo)
# Or use a local install
node ./node_modules/@stdiobus/workers-registry/launch acp-worker

Runtime Issues

Command not found:

# Verify installation
npm list @stdiobus/workers-registry

Worker crashes:

# Check stdio Bus logs
docker logs <container-name>

# Increase restart limits in config
{
  "limits": {
    "max_restarts": 10,
    "restart_window_sec": 120
  }
}

Connection refused:

# Verify stdio Bus is running
netstat -an | grep 9000

# Check Docker container status
docker ps | grep stdiobus

Contributing

Contributions are welcome! Please:

1. Fork the repository
2. Create a feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

Development setup:

git clone https://github.com/stdiobus/workers-registry
cd workers-registry
npm install
npm run build
npm test

Before submitting:

• All tests pass (npm test)
• Code follows existing style
• Documentation is updated
• Workers handle SIGTERM gracefully
• No output to stdout except NDJSON protocol messages

Resources

• stdio Bus kernel - Core protocol and daemon (source code)
• stdio Bus on Docker Hub - Docker images for easy deployment
• stdio Bus Full Documentation – Core protocol documentation
• ACP Registry - Available ACP agents
• Agent Client Protocol SDK - Official ACP SDK
• Model Context Protocol SDK - Official MCP SDK
• npm package - Package on npm registry

Worker Documentation

• ACP Worker - Full ACP protocol implementation
• ACP Registry Worker (acp-registry) - ACP Registry integration
• Echo Worker - Reference implementation
• MCP Echo Server - MCP server example
• MCP-to-ACP Proxy - Protocol bridge
• FAQ - Frequently asked questions

Support

• Issues: GitHub Issues
• Discussions: GitHub Discussions
• Repository: github.com/stdiobus/workers-registry

License

Apache License 2.0

Copyright (c) 2025–present Raman Marozau, Target Insight Function.

See LICENSE file for details.

Changelog

See CHANGELOG.md for version history and release notes.