roa 0.5.0-rc.6

Introduction

Roa is an async web framework inspired by koajs, lightweight but powerful.

Application

A Roa application is a structure composing and executing middlewares and an endpoint in a stack-like manner.

The obligatory hello world application:

use roa::{App, Context};
use roa::preload::*;
use log::info;
use std::error::Error as StdError;

async fn end(ctx: &mut Context) -> roa::Result {
    ctx.write("Hello, World");
    Ok(())
}

#[async_std::main]
async fn main() -> Result<(), Box<dyn StdError>> {
    let app = App::new(()).end(end);
    app.listen("127.0.0.1:8000", |addr| {
        info!("Server is listening on {}", addr)
    })?
    .await?;
    Ok(())
}

Cascading

Like koajs, middleware suspends and passes control to "downstream" by invoking next.await. Then control flows back "upstream" when next.await returns.

The following example responds with "Hello World", however first the request flows through the x-response-time and logging middleware to mark when the request started, then continue to yield control through the response endpoint. When a middleware invokes next the function suspends and passes control to the next middleware or endpoint. After the endpoint is called, the stack will unwind and each middleware is resumed to perform its upstream behaviour.

use roa::{App, Context, Next};
use roa::preload::*;
use log::info;
use std::error::Error as StdError;
use std::time::Instant;

#[async_std::main]
async fn main() -> Result<(), Box<dyn StdError>> {
    let app = App::new(())
        .gate(logger)
        .gate(x_response_time)
        .end(response);
    app.listen("127.0.0.1:8000", |addr| {
        info!("Server is listening on {}", addr)
    })?
    .await?;
    Ok(())
}

async fn logger(ctx: &mut Context, next: Next<'_>) -> roa::Result {
    next.await?;
    let rt = ctx.resp.must_get("x-response-time")?;
    info!("{} {} - {}", ctx.method(), ctx.uri(), rt);
    Ok(())
}

async fn x_response_time(ctx: &mut Context, next: Next<'_>) -> roa::Result {
    let start = Instant::now();
    next.await?;
    let ms = start.elapsed().as_millis();
    ctx.resp.insert("x-response-time", format!("{}ms", ms))?;
    Ok(())
}

async fn response(ctx: &mut Context) -> roa::Result {
    ctx.write("Hello, World");
    Ok(())
}

Status Handling

You can catch or straightly throw a status returned by next.

use roa::{App, Context, Next, throw};
use roa::preload::*;
use roa::http::StatusCode;
use async_std::task::spawn;
use log::info;

#[async_std::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let app = App::new(())
        .gate(catch)
        .gate(not_catch)
        .end(status);
    app.listen("127.0.0.1:8000", |addr| {
        info!("Server is listening on {}", addr)
    })?
    .await?;
    Ok(())
}

async fn catch(_ctx: &mut Context, next: Next<'_>) -> roa::Result {
    // catch
    if let Err(status) = next.await {
        // teapot is ok
        if status.status_code != StatusCode::IM_A_TEAPOT {
            return Err(status);
        }
    }
    Ok(())
}

async fn not_catch(ctx: &mut Context, next: Next<'_>) -> roa::Result {
    next.await?; // just throw
    unreachable!()
}

async fn status(ctx: &mut Context) -> roa::Result {
    throw!(StatusCode::IM_A_TEAPOT, "I'm a teapot!")
}

status_handler

App has an status_handler to handle status thrown by the top middleware. This is the status_handler:

use roa::{Context, Status};
pub fn status_handler<S>(ctx: &mut Context<S>, status: Status) {
    ctx.resp.status = status.status_code;
    if status.expose {
        ctx.resp.write(status.message);
    } else {
        log::error!("{}", status);
    }
}

Router.

Roa provides a configurable and nestable router.

use roa::preload::*;
use roa::router::{Router, get};
use roa::{App, Context};
use async_std::task::spawn;
use log::info;

#[async_std::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let router = Router::new()
        .on("/:id", get(end)); // get dynamic "/:id"
    let app = App::new(())
        .end(router.routes("/user")?); // route with prefix "/user"
    app.listen("127.0.0.1:8000", |addr| {
        info!("Server is listening on {}", addr)
    })?
    .await?;
    
    Ok(())
}

async fn end(ctx: &mut Context) -> roa::Result {
    // get "/user/1", then id == 1.
    let id: u64 = ctx.must_param("id")?.parse()?;
    // do something
    Ok(())
}

Query

Roa provides a middleware query_parser.

use roa::preload::*;
use roa::query::query_parser;
use roa::{App, Context};
use async_std::task::spawn;
use log::info;

async fn must(ctx: &mut Context) -> roa::Result {
    // request "/?id=1", then id == 1.
    let id: u64 = ctx.must_query("id")?.parse()?;
    Ok(())
}

#[async_std::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let app = App::new(())
        .gate(query_parser)
        .end(must);
    app.listen("127.0.0.1:8080", |addr| {
        info!("Server is listening on {}", addr)
    })?
    .await?;     
    Ok(())
}

Other modules

• body: dealing with body more conveniently.
• compress: supports transparent content compression.
• cookie: cookies getter or setter.
• cors: CORS support.
• forward: "X-Forwarded-*" parser.
• header: dealing with headers more conveniently.
• jwt: json web token support.
• logger: a logger middleware.
• tls: https supports.
• websocket: websocket supports.