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ra2a

Comprehensive Rust SDK for the Agent2Agent (A2A) Protocol — client transport, server framework, streaming, gRPC, and multi-backend task storage.

What is ra2a?​

ra2a implements the full A2A protocol specification (v0.3.0) with an idiomatic Rust API. It provides everything you need to build agents that discover each other, exchange tasks, and stream results.

Key Features​

  • Axum server — full A2A server with JSON-RPC endpoints, SSE streaming, and task lifecycle management.
  • reqwest client — discover agents, send messages, and stream responses.
  • gRPC transport — optional tonic/prost-based gRPC transport.
  • Task storage — in-memory (default), PostgreSQL, MySQL, or SQLite.
  • Push notifications — HMAC-SHA256 verified webhook push notifications.

Quick Start​

cargo add ra2a
use ra2a::client::{A2AClient, Client};

let client = A2AClient::new("https://agent.example.com")?;

// Discover agent capabilities
let card = client.get_agent_card().await?;
println!("Agent: {} — {}", card.name, card.description.unwrap_or_default());

// Send a message
let message = ra2a::types::Message::user_text("Hello!");
let mut stream = client.send_message(message).await?;

while let Some(event) = futures::StreamExt::next(&mut stream).await {
    println!("{:?}", event?);
}

Feature Flags​

FlagDefaultDescription
clientyesHTTP/JSON-RPC client, SSE streaming, card resolver
serveryesAxum HTTP server, event queue, task lifecycle
grpc—gRPC transport via tonic/prost
telemetry—OpenTelemetry tracing spans and metrics
postgresql—PostgreSQL task store via sqlx
mysql—MySQL task store via sqlx
sqlite—SQLite task store via sqlx
sql—All SQL backends
full—Everything
# Server with PostgreSQL and telemetry
ra2a = { version = "0.4", features = ["server", "postgresql", "telemetry"] }

# Client only
ra2a = { version = "0.4", default-features = false, features = ["client"] }

# Everything
ra2a = { version = "0.4", features = ["full"] }

Source Code​