eslrs is a pure Rust implementation of libesl, FreeSWITCH™'s Event Socket Library.

Features

• Async: Built on tokio for high-performance async I/O
• Inbound and Outbound: Support for both ESL connection modes
• Multiple Event Formats: JSON, plain text, and XML event parsing
• Instrumentation: Optional tracing/logging integration

Quick Start

Add eslrs as dependency and enable the json feature if planning to use json events.

eslrs = { version = "0.1", features = ["json"] }

Inbound and Outbound APIs

Inbound

use eslrs::{Inbound, Command, event::JsonEvent};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Connect and authenticate
    let mut conn = Inbound::connect("0.0.0.0:8021", "ClueCon").await?;

    // Send commands
    let reply = conn.send_recv(Command::api("status")).await?;
    println!("Status: {:?}", reply);

    // Subscribe to events
    conn.send_recv(Command::events_json("all")).await?;

    // Receive events
    loop {
        let event = conn.recv().await?;
        if event.is_json() && let Ok(json) = JsonEvent::try_from(event){
            println!("Event: {:?}", json);
        }
    }
}

Outbound

use eslrs::{Outbound, ESLConfig, Command};
use tokio::net::TcpListener;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let listener = TcpListener::bind("0.0.0.0:8888").await?;
    println!("Listening for FreeSWITCH connections...");

    loop {
        let (socket, _) = listener.accept().await?;
        tokio::spawn(async move {
            let config = ESLConfig::default();
            let mut conn = Outbound::handshake(socket, config).await.unwrap();

            // Get call info
            let info = conn.get_info().clone();
            let uuid = info.get_header("Unique-ID").unwrap();

            // Control the call
            conn.send_recv(Command::execute(uuid, "answer", "")).await.unwrap();
            conn.send_recv(Command::execute(uuid, "playback", "/tmp/hello.wav")).await.unwrap();
        });
    }
}

Logging and Tracing

The main api of the esl connection have been instrumented to feed into either logging or tracing eco-systems. The tracing feature is enabled by default, logging requires manual inclusion.

2025-10-23T14:57:21.225778Z  INFO tracing_example: Connecting to FreeSWITCH at 0.0.0.0:8021
2025-10-23T14:57:21.839107Z  INFO send_recv{command="auth ClueCon"}: eslrs::connection: return=Reply(RawEvent { headers: {"Content-Type": "command/reply", "Reply-Text": "+OK accepted"}, body: None })
2025-10-23T14:57:21.839399Z  INFO recv: eslrs::connection: return=Event(headers={"Content-Type": "auth/request"})