Bridge

A bridge library and application between Agent Client Protocol (ACP) agents and clients.

aptove-bridge can be used in two ways:

• Standalone binary — run bridge as a separate process that spawns your ACP agent over stdio and exposes it over WebSocket to mobile or desktop clients.
• Embedded library — add aptove-bridge as a Rust dependency and run the bridge server in-process alongside your agent, with no subprocess or stdio pipe required.

Transport Modes

| Mode | Use Case | Documentation | |------|----------|---------------| | Local | Same Wi-Fi network, secure pairing with QR code | docs/transport/local.md | | Cloudflare | Remote access via Cloudflare Zero Trust (internet-accessible) | docs/transport/cloudflare.md | | Tailscale | Private overlay network via MagicDNS + HTTPS (Recommended) | docs/transport/tailscale.md |

One transport is active at a time. When multiple are enabled in common.toml, the bridge prompts you to select one at startup.

Features

• 📱 QR Code Pairing: Secure one-time code pairing via QR scan
• 🔒 TLS + Certificate Pinning: Self-signed certificates with fingerprint validation
• ⚡ WebSocket Streaming: Real-time bidirectional communication
• 🌐 Multi-Transport: Local, Cloudflare, Tailscale — configure and switch between them
• 🔑 Stable Agent Identity: agent_id UUID persisted in common.toml for multi-transport dedup on mobile
• 🦀 Embeddable: Use as a library with StdioBridge for in-process deployment

Using as a Library

Add to your Cargo.toml:

[dependencies]
aptove-bridge = "0.2"

Minimal Example

use aptove_bridge::{
    bridge::StdioBridge,
    common_config::CommonConfig,
    tls::TlsConfig,
};

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    // Load (or initialise) shared config — generates agent_id and auth_token on first run
    let mut config = CommonConfig::load()?;
    config.ensure_agent_id();
    config.ensure_auth_token();
    config.save()?;

    // Generate (or load) a self-signed TLS cert
    let tls = TlsConfig::load_or_generate(&CommonConfig::config_dir(), &[])?;

    StdioBridge::new("copilot --acp".to_string(), 8765)
        .with_auth_token(Some(config.auth_token.clone()))
        .with_tls(tls)
        .start()
        .await
}

StdioBridge Builder Methods

| Method | Description | |--------|-------------| | new(agent_command, port) | Create a bridge that spawns the given command; listen on port | | .with_bind_addr(addr) | Override bind address (default: "0.0.0.0") | | .with_auth_token(token) | Require a bearer token for connections | | .with_tls(tls_config) | Enable TLS with a TlsConfig (self-signed cert) | | .with_external_tls() | Signal that TLS is handled upstream (Tailscale Serve, Cloudflare) | | .with_pairing(manager) | Enable QR pairing via a PairingManager | | .with_agent_pool(pool) | Enable keep-alive sessions via an AgentPool | | .with_working_dir(dir) | Set the working directory for the spawned agent process | | .with_push_relay(client) | Enable push notifications via a relay | | .with_webhook_resolver(fn) | Handle POST /webhook/<token> trigger requests | | .start() | Start the WebSocket listener (runs until shutdown) |

Standalone Binary

Quick Start

# Build
cargo build --release

# Start the bridge — interactive agent selection menu
./target/release/bridge

# Or specify the agent directly
./target/release/bridge run --agent-command "copilot --acp"

Running bridge with no subcommand defaults to run. When --agent-command is omitted, an interactive menu lets you pick from known agents (Copilot, Gemini, Goose) or enter a custom command.

Scan the QR code with the mobile app to connect.

Configuration — common.toml

All transport settings live in common.toml. The file is created automatically with local transport enabled on first run.

Default location:

| Platform | Path | |----------|------| | macOS | ~/Library/Application Support/com.aptove.bridge/common.toml | | Linux | ~/.config/bridge/common.toml |

Override with -c / --config-dir:

bridge -c ./my-config run --agent-command "copilot --acp"

Example common.toml

agent_id   = "550e8400-e29b-41d4-a716-446655440000"  # auto-generated UUID
auth_token = "base64urltoken"                         # auto-generated

[transports.local]
enabled = true
port    = 8765
tls     = true

[transports.cloudflare]
enabled       = true
hostname      = "https://agent.example.com"
tunnel_id     = "abc123"
tunnel_secret = "..."
account_id    = "..."
client_id     = "client.access"
client_secret = "xxxxx"

[transports.tailscale-serve]
enabled = true

Enable only the transports you need. agent_id and auth_token are generated automatically on first run and stay stable across restarts.

Config Directory Files

All bridge state lives in the config directory. These files are created automatically on first run:

| File | Purpose | |------|---------| | common.toml | Main config — agent_id, auth_token, and transport settings. Permissions 0600. | | cert.pem | Self-signed TLS certificate for the local transport WebSocket server. Its fingerprint is embedded in the QR pairing payload for certificate pinning. | | key.pem | Private key for the TLS certificate. | | cert-extra-sans.json | Tracks extra Subject Alternative Names (IPs/hostnames) baked into the TLS cert (e.g. --advertise-addr or Tailscale IP). When these change, the cert is automatically regenerated. |

Commands

run — Start the bridge (default)

run is the default subcommand — running bridge with no arguments is equivalent to bridge run.

# Interactive agent selection
bridge

# Or specify the agent directly
bridge run --agent-command "copilot --acp"

| Flag | Short | Description | Default | |------|-------|-------------|---------| | --agent-command <CMD> | -a | Command to spawn the ACP agent | Interactive menu | | --bind <ADDR> | -b | Address to bind the listener | 0.0.0.0 | | --verbose | | Enable info-level logging | Off (warn only) | | --advertise-addr <ADDR> | | Override LAN address in QR pairing URL | Auto-detected |

When --agent-command is omitted, the bridge presents an interactive menu:

Select an agent to run:
  [1] Copilot  (copilot --acp)
  [2] Gemini   (gemini --experimental-acp)
  [3] Goose    (goose acp)
  [4] Custom
Enter number [1]:

The QR code for pairing is always displayed at startup.

Transport selection, port, TLS, and auth token are all read from common.toml.

show-qr — Show QR code for a second device

bridge show-qr

Displays the connection QR code for the currently active transport. The bridge must already be running. Use this to pair an additional device without restarting.

setup — Provision Cloudflare infrastructure

bridge setup \
  --api-token  "your-api-token" \
  --account-id "your-account-id" \
  --domain     "example.com" \
  --subdomain  "agent"

Creates the Cloudflare tunnel, DNS record, Access Application, and Service Token. Saves credentials to common.toml under [transports.cloudflare]. Only needed once.

| Flag | Description | Default | |------|-------------|---------| | --api-token <TOKEN> | Cloudflare API token | Required | | --account-id <ID> | Cloudflare account ID | Required | | --domain <DOMAIN> | Domain managed by Cloudflare | Required | | --subdomain <SUB> | Subdomain for the bridge endpoint | agent | | --tunnel-name <NAME> | Name for the Cloudflare tunnel | aptove-tunnel |

status — Check configuration

bridge status

Prints the active common.toml path, agent_id, enabled transports, and Tailscale availability.

Architecture

Standalone

┌─────────────┐                    ┌───────────────────────┐        ┌──────────────┐
│  Client App │◄──────────────────►│  bridge binary        │◄──────►│  ACP Agent   │
│ (iOS/Android│  WebSocket (TLS)   │  (transport listener) │  stdio │  (your cmd)  │
└─────────────┘                    └───────────────────────┘        └──────────────┘

Embedded (library)

┌─────────────┐                    ┌──────────────────────────────────┐        ┌──────────────┐
│  Client App │◄──────────────────►│  Your process                    │◄──────►│  ACP Agent   │
│ (iOS/Android│  WebSocket (TLS)   │  StdioBridge (transport listener)│  stdio │  (your cmd)  │
└─────────────┘                    └──────────────────────────────────┘        └──────────────┘

The agent process is still spawned as a subprocess via stdio — StdioBridge handles the WebSocket server, TLS, auth, and pairing in-process alongside your application.

Troubleshooting

| Symptom | Cause | Fix | |---------|-------|-----| | QR code not scanning | Phone camera can't read terminal QR | Increase terminal font size, or copy the pairing URL and open manually | | "Unauthorized" on connect | Wrong or missing auth token | Re-scan QR code | | TLS handshake failure | Certificate mismatch | Delete the config dir and restart to regenerate certs; re-pair the device | | App cannot reach bridge | Firewall blocking the port | Check OS firewall; ensure the port in common.toml is open | | Transport fails to start | common.toml has no enabled = true transport | Run bridge status to see configured transports |

Debugging

# Enable verbose logging
bridge run --verbose

# Check which transports are configured
bridge status

# Test agent command independently
echo '{"jsonrpc":"2.0","method":"initialize","id":1}' | copilot --acp

Testing with Other ACP-Compatible Agents

Please note that the project is extensively tested only with Copilot CLI. Open a bug report if you notice any issues with other ACP-Compatible Agents.

The easiest way to test any supported agent is to run bridge and pick it from the interactive menu. Alternatively, pass the command directly:

bridge run -a "gemini --experimental-acp" --verbose
bridge run -a "goose acp" --verbose

Security

• Auth token: auto-generated 32-byte random value, stored in common.toml (0600). Transmitted to mobile during QR pairing and stored in the device Keychain.
• TLS: self-signed certificate generated on first run. Certificate fingerprint is included in the QR pairing payload and pinned by the mobile app to prevent MITM attacks.
• Pairing codes: 6-digit, single-use, expire after 60 seconds. Rate-limited to 5 attempts per code.
• common.toml: contains all secrets. Permissions are set to 0600 automatically. Keep it secure.
• Agent command: the --agent-command value (or interactive menu selection) is validated at startup — the binary must exist and be executable before the server accepts connections. The command is never persisted to common.toml; it must be supplied each time the bridge is started. The bridge is an operator tool: whoever can invoke it already has local shell access, so the agent command is implicitly trusted to the same degree as any other command that user could run.

To rotate credentials (invalidates all paired devices):

# macOS
rm ~/Library/Application\ Support/com.aptove.bridge/common.toml
# Linux
rm ~/.config/bridge/common.toml

bridge

Development

cargo build --release    # Build
cargo test               # Run tests

License

Apache 2.0 — see LICENSE