VTCode ACP Client

HTTP-based Agent Communication Protocol (ACP) client library for inter-agent communication in distributed agent systems.

Features

✓ REST-based Communication - Standard HTTP protocol, no special SDKs required ✓ Agent Discovery - Find agents by capability or ID ✓ Sync & Async - Both synchronous and asynchronous request handling ✓ Health Monitoring - Ping agents to check status ✓ Message Serialization - Type-safe ACP message handling ✓ Registry Management - In-memory agent registry with lifecycle management ✓ Error Handling - Comprehensive error types for debugging

Quick Start

Add to Cargo.toml

[dependencies]
vtcode-acp-client = { path = "../vtcode-acp-client" }

Basic Usage

use vtcode_acp_client::{AcpClient, AgentInfo};
use serde_json::json;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    // Create client
    let client = AcpClient::new("my-agent".to_string())?;
    
    // Register a remote agent
    let agent = AgentInfo {
        id: "remote-agent".to_string(),
        name: "Remote Agent".to_string(),
        base_url: "http://localhost:8081".to_string(),
        description: Some("A sample remote agent".to_string()),
        capabilities: vec!["bash".to_string()],
        metadata: Default::default(),
        online: true,
        last_seen: None,
    };
    
    client.registry().register(agent).await?;
    
    // Call the remote agent
    let result = client.call_sync(
        "remote-agent",
        "execute".to_string(),
        json!({"cmd": "echo hello"}),
    ).await?;
    
    println!("Result: {}", result);
    Ok(())
}

Module Overview

Core Components

AcpClient

Main client for agent communication.

// Create a new client
let client = AcpClient::new("local-agent-id".to_string())?;

// Synchronous call (waits for response)
let result = client.call_sync("remote-id", "action".to_string(), args).await?;

// Asynchronous call (returns message_id immediately)
let msg_id = client.call_async("remote-id", "action".to_string(), args).await?;

// Health check
let is_online = client.ping("remote-id").await?;

// Discover remote agent
let agent_info = client.discover_agent("http://remote:8080").await?;

AgentRegistry

In-memory registry of available agents.

let registry = client.registry();

// Register agent
registry.register(agent).await?;

// Find agent
let agent = registry.find("agent-id").await?;

// Find by capability
let agents = registry.find_by_capability("python").await?;

// List all/online agents
let all = registry.list_all().await?;
let online = registry.list_online().await?;

// Update status
registry.update_status("agent-id", false).await?;

AcpMessage

Type-safe message handling.

// Create request
let msg = AcpMessage::request(
    "sender".to_string(),
    "recipient".to_string(),
    "action".to_string(),
    json!({}),
);

// Serialize to JSON
let json = msg.to_json()?;

// Deserialize from JSON
let msg = AcpMessage::from_json(&json)?;

Error Handling

use vtcode_acp_client::AcpError;

match client.call_sync("agent", "action".to_string(), args).await {
    Ok(result) => println!("Success: {}", result),
    Err(AcpError::AgentNotFound(id)) => println!("Agent {} not found", id),
    Err(AcpError::NetworkError(e)) => println!("Network error: {}", e),
    Err(AcpError::Timeout(e)) => println!("Timeout: {}", e),
    Err(AcpError::RemoteError { agent_id, message, code }) => {
        println!("Remote error from {}: {} (code: {:?})", agent_id, message, code);
    }
    Err(e) => println!("Error: {}", e),
}

Architecture

User Code
   │
   └─► AcpClient
        ├─► HTTP Communication (reqwest)
        ├─► Message Serialization (serde_json)
        └─► AgentRegistry
             └─► In-memory HashMap<String, AgentInfo>

Message Protocol

Request

{
  "id": "uuid",
  "type": "request",
  "sender": "local-agent",
  "recipient": "remote-agent",
  "content": {
    "action": "execute_tool",
    "args": { "param": "value" },
    "sync": true,
    "timeout_secs": 30
  },
  "timestamp": "2024-01-01T12:00:00Z",
  "correlation_id": null
}

Response

{
  "id": "uuid",
  "type": "response",
  "sender": "remote-agent",
  "recipient": "local-agent",
  "content": {
    "status": "success",
    "result": { "output": "data" },
    "execution_time_ms": 245
  },
  "timestamp": "2024-01-01T12:00:00Z",
  "correlation_id": "request-id"
}

Remote Agent Requirements

For an agent to be callable, it must implement:

1. POST /messages

Handle ACP requests and return responses.

app.post("/messages", |msg: AcpMessage| async {
    // Process message
    // Return AcpResponse
})

2. GET /metadata

Return agent discovery information.

app.get("/metadata", || async {
    AgentInfo {
        id: "agent-id".to_string(),
        name: "Agent Name".to_string(),
        base_url: "http://localhost:8080".to_string(),
        // ... other fields
    }
})

3. GET /health

Simple health check endpoint.

app.get("/health", || "OK")

Configuration

Build client with custom timeout:

use std::time::Duration;
use vtcode_acp_client::AcpClientBuilder;

let client = AcpClientBuilder::new("local-agent".to_string())
    .with_timeout(Duration::from_secs(60))
    .build()?;

Testing

Run tests:

cargo test -p vtcode-acp-client

Run example:

cargo run --example acp_distributed_workflow

Performance

• Message serialization: <1ms
• Local registry lookup: O(1)
• HTTP timeout: Configurable (default 30s)
• Async overhead: Minimal (uses tokio)

Security Considerations

⚠️ Current Implementation:

• HTTP (not HTTPS) by default
• No authentication/authorization
• No message encryption
• Messages logged with tracing

🔒 Recommended for Production:

• Use HTTPS with certificate pinning
• Implement JWT or mTLS authentication
• Add message signing and encryption
• Implement rate limiting
• Add audit logging
• Use VPN/private networks

Roadmap

• HTTPS/TLS support
• Authentication plugins (JWT, mTLS)
• Message encryption
• Automatic retries with exponential backoff
• Circuit breaker pattern
• Message queuing
• OpenTelemetry integration
• Metrics collection

Integration with VTCode

The ACP client is exposed to the main agent through three MCP tools:

1. acp_call - Call remote agents
2. acp_discover - Discover agents
3. acp_health - Check agent health

See ACP_INTEGRATION.md for integration details.

References

• ACP Official Specification
• VTCode Documentation
• Examples

License

MIT