roa 0.5.0-beta.2

Introduction

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

Application

A Roa application is a structure containing a middleware group which composes and executes middleware functions in a stack-like manner.

The obligatory hello world application:

use roa::App;
use roa::preload::*;
use log::info;
use std::error::Error as StdError;

#[async_std::main]
async fn main() -> Result<(), Box<dyn StdError>> {
let mut app = App::new(());
app.end(|mut ctx| async move {
ctx.write_text("Hello, World")
});
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 middleware. When a middleware invokes next the function suspends and passes control to the next middleware defined. After there are no more middleware to execute downstream, the stack will unwind and each middleware is resumed to perform its upstream behaviour.

use roa::App;
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 mut app = App::new(());
// logger
app.gate_fn(|ctx, next| async move {
next.await?;
let rt = ctx.resp().must_get("x-response-time")?;
info!("{} {} - {}", ctx.method(), ctx.uri(), rt);
Ok(())
});

// x-response-time
app.gate_fn(|mut ctx, next| async move {
let start = Instant::now();
next.await?;
let ms = start.elapsed().as_millis();
ctx.resp_mut().insert("x-response-time", format!("{}ms", ms))?;
Ok(())
});

// response
app.end(|mut ctx| async move {
ctx.write_text("Hello, World")
});

app.listen("127.0.0.1:8000", |addr| {
info!("Server is listening on {}", addr)
})?
.await?;
Ok(())
}

Error Handling

You can catch or straightly throw an error returned by next.

use roa::{App, 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>> {
App::new(())
.gate_fn(|ctx, next| async move {
// catch
if let Err(err) = next.await {
// teapot is ok
if err.status_code != StatusCode::IM_A_TEAPOT {
return Err(err)
}
}
Ok(())
})
.gate_fn(|ctx, next| async move {
next.await?; // just throw
unreachable!()
})
.end(|_ctx| async move {
throw!(StatusCode::IM_A_TEAPOT, "I'm a teapot!")
})
.listen("127.0.0.1:8000", |addr| {
info!("Server is listening on {}", addr)
})?
.await?;
Ok(())
}

error_handler

App has an error_handler to handle error thrown by the top middleware. This is the error_handler:

use roa_core::{Context, Error, Result, State, ErrorKind};
pub async fn error_handler<S: State>(mut context: Context<S>, err: Error) -> Result {
// set status code to err.status_code.
context.resp_mut().status = err.status_code;
if err.expose {
// write err.message to response body if err.expose.
context.resp_mut().write(err.message.clone());
}
if err.kind == ErrorKind::ServerError {
// thrown to hyper
Err(err)
} else {
// caught
Ok(())
}
}

The error thrown by this error_handler will be handled by hyper.

Router.

Roa provides a configurable and nestable router.

use roa::preload::*;
use roa::router::Router;
use roa::App;
use async_std::task::spawn;
use log::info;

#[async_std::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
let mut router = Router::<()>::new();
// get dynamic "/:id"
router.get("/:id", |ctx| async move {
let id: u64 = ctx.must_param("id")?.parse()?;
// do something
Ok(())
});
App::new(())
// route with prefix "/user"
.gate(router.routes("/user")?)
.listen("127.0.0.1:8000", |addr| {
info!("Server is listening on {}", addr)
})?
.await?;

// get "/user/1", then id == 1.
Ok(())
}

Query

Roa provides a middleware query_parser.

use roa::preload::*;
use roa::query::query_parser;
use roa::App;
use async_std::task::spawn;
use log::info;

#[async_std::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
App::new(())
.gate(query_parser)
.end( |ctx| async move {
let id: u64 = ctx.must_query("id")?.parse()?;
Ok(())
})
.listen("127.0.0.1:8080", |addr| {
info!("Server is listening on {}", addr)
})?
.await?;     
// request "/?id=1", then id == 1.
Ok(())
}

Other modules

• body: dealing with body more conviniently.
• compress: supports transparent content compression.
• cors: CORS support.
• forward: "X-Forwarded-*" parser.
• header: dealing with headers more conviniently.
• jwt: json web token support.
• logger: a logger middleware.