rs-netty 1.1.0

Overview

rs-netty is a small Rust networking framework that keeps the useful parts of Netty's Channel / Pipeline / Handler model while rebuilding the main path around Rust ownership, async/await, Tokio tasks, typed messages, and bounded queues.

The core idea is simple: a pipeline is not a dynamically reordered bag of handlers. It is a typed sequence:

codec -> inbound* -> business* -> handler -> outbound*

Invalid stage order, message mismatches, and TCP/UDP pipeline mixups are caught by the Rust type checker instead of failing at runtime.

Highlights

• Tokio-native: built on Tokio TCP/UDP sockets, tasks, channels, and async IO rather than a Java-style event loop abstraction.
• Netty-inspired model: use channels, pipelines, handlers, codecs, lifecycle hooks, and write/flush semantics in a Rust-shaped API.
• Typed pipeline construction: builder states enforce codec -> inbound* -> business* -> handler -> outbound* at compile time.
• Separate TCP and UDP builders: stream pipelines and datagram pipelines are different types, so they cannot be accidentally mixed.
• Bounded outbound queues: channels use bounded Tokio queues to make backpressure visible instead of allowing unbounded writes.
• Graceful shutdown and lifecycle hooks: servers expose shutdown handles and optional hooks for server, connection, and socket lifecycle events.
• Zero unsafe: the crate does not use unsafe.
• Practical codecs and examples: TCP, UDP, JSON, HTTP, MQTT, WebSocket, typed chains, lifecycle hooks, benchmarks, and compile-fail tests are included.

Quick Start

Add the crate:

[dependencies]
rs-netty = "1.0.0"
tokio = { version = "1", features = ["rt-multi-thread", "macros"] }

The default feature set includes rs-netty-macros, which provides the #[handler] macro used in the examples below.

TCP Example

Build a typed TCP line echo server:

use rs_netty::{codec::LineCodec, handler, pipeline, Result, TcpServer};

#[tokio::main]
async fn main() -> Result<()> {
    TcpServer::bind("127.0.0.1:9000")
        .pipeline(|| {
            pipeline()
                .codec(LineCodec::new())
                .handler(Echo)
        })
        .run()
        .await
}

struct Echo;

#[handler(Echo)]
async fn echo(msg: String) -> Result<String> {
    Ok(msg)
}

Talk to it with a typed TCP client:

use rs_netty::{codec::LineCodec, handler, pipeline, Result, TcpClient};
use tokio::sync::oneshot;

#[tokio::main]
async fn main() -> Result<()> {
    let (tx, rx) = oneshot::channel();

    let client = TcpClient::connect("127.0.0.1:9000")
        .pipeline_instance(
            pipeline()
                .codec(LineCodec::new())
                .handler(PrintResponse { done: Some(tx) }),
        )
        .run()
        .await?;

    client.write_and_flush("hello".to_string()).await?;
    let _ = rx.await;
    client.close().await?;
    client.wait().await
}

struct PrintResponse {
    done: Option<oneshot::Sender<()>>,
}

#[handler(PrintResponse, write = String)]
async fn print_response(handler: &mut PrintResponse, msg: String) -> Result<()> {
    println!("server -> {msg}");
    if let Some(done) = handler.done.take() {
        let _ = done.send(());
    }
    Ok(())
}

UDP Example

UDP uses a datagram pipeline and a datagram codec:

use rs_netty::{
    codec::Utf8DatagramCodec, datagram_pipeline, DatagramContext, DatagramHandler, Result,
    UdpServer,
};

#[tokio::main]
async fn main() -> Result<()> {
    UdpServer::bind("127.0.0.1:9002")
        .pipeline(|| {
            datagram_pipeline()
                .codec(Utf8DatagramCodec)
                .handler(UdpEcho)
        })
        .run()
        .await
}

struct UdpEcho;

impl DatagramHandler<String> for UdpEcho {
    type Write = String;

    async fn read(&mut self, ctx: &mut DatagramContext<Self::Write>, msg: String) -> Result<()> {
        ctx.write_and_flush(format!("echo: {msg}")).await
    }
}

UDP support is socket-oriented. UdpServer uses one socket-level pipeline and does not create per-peer child pipelines. If you need per-peer state, store it in your handler, for example with a HashMap<SocketAddr, PeerState>.

TLS Example

TLS is a TCP transport layer, not a pipeline codec. Enable the tls feature, build a server or client context, and attach it with .tls(...) before running the same typed pipeline:

[dependencies]
rs-netty = { version = "1.0.0", features = ["tls"] }

use rs_netty::{codec::LineCodec, pipeline, Result, TcpServer, TlsContextBuilder};

#[tokio::main]
async fn main() -> Result<()> {
    let tls = TlsContextBuilder::for_server()
        .certificate_chain_pem(include_bytes!("certs/server-chain.pem"))
        .private_key_pem(include_bytes!("certs/server-key.pem"))
        .build()?;

    TcpServer::bind("127.0.0.1:9443")
        .tls(tls)
        .pipeline(|| pipeline().codec(LineCodec::new()).handler(Echo))
        .run()
        .await
}

Client trust is selected with a typestate builder, so TlsContextBuilder::for_client().build() does not compile until you choose a trust strategy such as root_certificate_pem, native_roots, webpki_roots, or the feature-gated development helper danger_accept_invalid_certs.

For required mTLS, configure trusted client roots on the server and a client identity on the client:

let server_tls = TlsContextBuilder::for_server()
    .certificate_chain_pem(include_bytes!("certs/server-chain.pem"))
    .private_key_pem(include_bytes!("certs/server-key.pem"))
    .client_auth_required_pem(include_bytes!("certs/client-ca.pem"))
    .build()?;

let client_tls = TlsContextBuilder::for_client()
    .root_certificate_pem(include_bytes!("certs/server-ca.pem"))
    .client_identity_pem(
        include_bytes!("certs/client-chain.pem"),
        include_bytes!("certs/client-key.pem"),
    )
    .server_name("localhost")
    .build()?;

For optional mTLS, use client_auth_optional_pem or client_auth_optional_der. Clients may connect without a certificate, while a certificate is still verified when one is presented:

let server_tls = TlsContextBuilder::for_server()
    .certificate_chain_pem(include_bytes!("certs/server-chain.pem"))
    .private_key_pem(include_bytes!("certs/server-key.pem"))
    .client_auth_optional_pem(include_bytes!("certs/client-ca.pem"))
    .build()?;

Servers and clients can advertise ALPN protocols with alpn_protocols. A selected protocol is exposed through TlsInfo; if both sides configure ALPN but there is no common protocol, the TLS handshake fails.

let server_tls = TlsContextBuilder::for_server()
    .certificate_chain_pem(include_bytes!("certs/server-chain.pem"))
    .private_key_pem(include_bytes!("certs/server-key.pem"))
    .alpn_protocols([b"h2".as_slice(), b"http/1.1".as_slice()])
    .build()?;

One listener can serve multiple certificate identities with SNI. Configure a default certificate as the fallback, then add named identities with sni_certificate_pem or sni_certificate_der:

let server_tls = TlsContextBuilder::for_server()
    .certificate_chain_pem(include_bytes!("certs/default-chain.pem"))
    .private_key_pem(include_bytes!("certs/default-key.pem"))
    .sni_certificate_pem(
        "api.example.com",
        include_bytes!("certs/api-chain.pem"),
        include_bytes!("certs/api-key.pem"),
    )
    .build()?;

When TLS is negotiated, ctx.tls() returns TlsInfo from TCP handlers and stream transformation contexts. ConnInfo::tls() also exposes the same metadata to lifecycle hooks. TlsInfo includes the peer certificate chain, the selected ALPN protocol, and the effective server name or server-side SNI.

Typed Pipeline Model

TCP stream pipelines start with pipeline():

pipeline()
  .codec(...)
  .inbound(...)*
  .business(...)*
  .handler(...)
  .outbound(...)*

UDP datagram pipelines start with datagram_pipeline():

datagram_pipeline()
  .codec(...)
  .inbound(...)*
  .business(...)*
  .handler(...)
  .outbound(...)*

The builders expose methods only in valid states. Message transitions are checked with trait bounds, so:

• a handler input must match the previous inbound/business output;
• outbound input must match Handler::Write or DatagramHandler::Write;
• the final outbound type must be encodable by the selected codec;
• TcpServer / TcpClient accept only stream pipelines;
• UdpServer / UdpClient accept only datagram pipelines.

This is intentionally different from Java Netty's dynamic pipeline. The Rust API trades runtime handler mutation for compile-time ordering and message checks.

Built-In Codecs

Stream codecs and stages:

• LineCodec
• LengthFieldBasedFrameDecoder
• LengthFieldPrepender
• FixedLengthFrameDecoder
• DelimiterBasedFrameDecoder
• ByteArrayDecoder
• ByteArrayEncoder
• HttpCodec
• MqttCodec
• WebSocketCodec and HttpWsCodec behind the websocket feature
• JsonDecode<T> and JsonEncode<T> behind the json feature

Datagram codecs:

• Utf8DatagramCodec
• BytesDatagramCodec

JSON is modeled as ordinary pipeline stages, so framing and serialization remain separate:

[dependencies]
rs-netty = { version = "1.0.0", features = ["json"] }
serde = { version = "1", features = ["derive"] }

use rs_netty::{
    codec::{JsonDecode, JsonEncode, LineCodec},
    handler, pipeline,
};

#[derive(serde::Deserialize)]
struct Request {
    op: String,
}

#[derive(serde::Serialize)]
struct Response {
    ok: bool,
}

struct ApiHandler;

#[handler(ApiHandler)]
async fn handle_api(_req: Request) -> rs_netty::Result<Response> {
    Ok(Response { ok: true })
}

let pipeline = pipeline()
    .codec(LineCodec::new())
    .inbound(JsonDecode::<Request>::new())
    .handler(ApiHandler)
    .outbound(JsonEncode::<Response>::new());

Lifecycle / Shutdown / Backpressure

Servers and clients can attach optional lifecycle hooks with .life(...). Applications that do not need hooks use the default NoLife.

use std::net::SocketAddr;

use rs_netty::{codec::LineCodec, pipeline, Life, Result, TcpServer};

#[derive(Clone, Copy)]
struct TraceLife;

impl Life for TraceLife {
    async fn tcp_server_started(&self, local_addr: SocketAddr) -> Result<()> {
        tracing::info!(%local_addr, "tcp server started");
        Ok(())
    }
}

TcpServer::bind("127.0.0.1:9000")
    .pipeline(|| {
        pipeline()
            .codec(LineCodec::new())
            .handler(MyHandler)
    })
    .life(TraceLife)
    .run()
    .await

Servers also support external shutdown handles:

let server = TcpServer::bind("127.0.0.1:9000")
    .pipeline(|| {
        pipeline()
            .codec(LineCodec::new())
            .handler(MyHandler)
    })
    .start()
    .await?;

server.shutdown();
server.wait().await?;

Channel, Context, DatagramChannel, and DatagramContext expose write, flush, and write_and_flush:

• write stages outbound messages;
• flush pushes staged messages to the socket task;
• write_and_flush does both;
• a completed flush means the local socket write/send path completed, not that the remote peer acknowledged the message.

Outbound queues are bounded. Server and client builders expose .outbound_queue_size(...) when you need to tune queue capacity.

Benchmarks

The repository includes benchmark harnesses for rs-netty, bare Tokio, and Java Netty under benchmarks/. They measure throughput, latency percentiles, and server RSS for TCP line echo, TCP length-field echo, and UDP echo scenarios.

The table below comes from one local non-loopback run with TCP rows using TCP_NODELAY=true, 100 connections, 1,000,000 messages, 128-byte payloads, in-flight 16, and 100,000 untimed Netty warmup messages. UDP rows used 100 clients, 1,000,000 datagrams, 128-byte payloads, and 100,000 untimed Netty warmup datagrams. Treat these numbers as a directional snapshot, not a universal performance promise.

• Benchmark notes, Chinese
• Benchmark notes, English

Examples

Run the examples from the repository root:

cargo run --example tcp_echo_server
cargo run --example tcp_echo_client
cargo run --example tcp_json_line_echo --features json
cargo run --example tcp_lifecycle
cargo run --example tcp_tls_echo --features tls
cargo run --example tcp_typed_chain
cargo run --example tcp_typed_chain_client
cargo run --example udp_echo_server
cargo run --example udp_echo_client
cargo run --example udp_typed_chain
cargo run --example udp_typed_chain_client
cargo run --example websocket_server --features websocket
cargo run --example http_websocket_server --features websocket

Non-Goals

rs-netty deliberately does not expose or implement some Java Netty patterns on the main path:

• No public EventLoop API.
• No reference-counted ByteBuf API.
• No ChannelFuture / Promise API.
• No dynamic Box<dyn Handler> main path.
• No TLS pipeline stage; TLS, required/optional mTLS, ALPN, and SNI are optional TCP transport capabilities.
• No codec registry.
• No automatic UDP reliability, ordering, or retransmission.
• No per-peer UDP child pipeline.

License

Licensed under the Apache License, Version 2.0. See LICENSE.