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some more guide

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Nikolay Kim 2017-12-01 23:06:15 -08:00
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guide/src/SUMMARY.md
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[Quickstart](./qs_1.md)
- [Getting Started](./qs_2.md)
- [Actix web overview](./qs_3.md)
- [Actix application](./qs_3.md)
- [Handler](./qs_4.md)
- [Resources and Routes](./qs_5.md)
- [Application state](./qs_6.md)

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guide/src/qs_3.md
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# [WIP] Overview
# Application
Actix web provides some primitives to build web servers and applications with Rust.
It provides routing, middlewares, pre-processing of requests, and post-processing of responses,
websocket protcol handling, multipart streams, etc.
## Application
All actix web server is built around `Application` instance.
It is used for registering handlers for routes and resources, middlewares.
Also it stores applicationspecific state that is shared accross all handlers
@ -23,178 +20,3 @@ has same url path prefix:
In this example application with `/prefix` prefix and `index.html` resource
get created. This resource is available as on `/prefix/index.html` url.
### Application state
Application state is shared with all routes within same application.
State could be accessed with `HttpRequest::state()` method. It is read-only
but interior mutability pattern with `RefCell` could be used to archive state mutability.
State could be accessed with `HttpRequest::state()` method or
`HttpContext::state()` in case of http actor.
Let's write simple application that uses shared state. We are going to store requests count
in the state:
```rust
extern crate actix;
extern crate actix_web;
use std::cell::Cell;
use actix_web::*;
// This struct represents state
struct AppState {
counter: Cell<usize>,
}
fn index(req: HttpRequest<AppState>) -> String {
let count = req.state().counter.get() + 1; // <- get count
req.state().counter.set(count); // <- store new count in state
format!("Request number: {}", count) // <- response with count
}
fn main() {
Application::build("/", AppState{counter: Cell::new(0)})
.resource("/", |r| r.handler(Method::GET, index))
.finish();
}
```
## [WIP] Handler
A request handler can by any object that implements
[`Handler` trait](../actix_web/struct.HttpResponse.html#implementations).
By default actix provdes several `Handler` implementations:
* Simple function that accepts `HttpRequest` and returns any object that
can be converted to `HttpResponse`
* Function that accepts `HttpRequest` and returns `Result<Reply, Into<Error>>` object.
* Function that accepts `HttpRequest` and return actor that has `HttpContext<A>`as a context.
Actix provides response conversion into `HttpResponse` for some standard types,
like `&'static str`, `String`, etc.
For complete list of implementations check
[HttpResponse documentation](../actix_web/struct.HttpResponse.html#implementations).
Examples:
```rust,ignore
fn index(req: HttpRequest) -> &'static str {
"Hello world!"
}
```
```rust,ignore
fn index(req: HttpRequest) -> String {
"Hello world!".to_owned()
}
```
```rust,ignore
fn index(req: HttpRequest) -> Bytes {
Bytes::from_static("Hello world!")
}
```
```rust,ignore
fn index(req: HttpRequest) -> Box<Future<Item=HttpResponse, Error=Error>> {
...
}
```
### Custom conversion
Let's create response for custom type that serializes to `application/json` response:
```rust
extern crate actix;
extern crate actix_web;
extern crate serde;
extern crate serde_json;
#[macro_use] extern crate serde_derive;
use actix_web::*;
#[derive(Serialize)]
struct MyObj {
name: String,
}
/// we have to convert Error into HttpResponse as well, but with
/// specialization this could be handled genericly.
impl Into<HttpResponse> for MyObj {
fn into(self) -> HttpResponse {
let body = match serde_json::to_string(&self) {
Err(err) => return Error::from(err).into(),
Ok(body) => body,
};
// Create response and set content type
HttpResponse::Ok()
.content_type("application/json")
.body(body).unwrap()
}
}
fn main() {
let sys = actix::System::new("example");
HttpServer::new(
Application::default("/")
.resource("/", |r| r.handler(
Method::GET, |req| {MyObj{name: "user".to_owned()}})))
.serve::<_, ()>("127.0.0.1:8088").unwrap();
println!("Started http server: 127.0.0.1:8088");
actix::Arbiter::system().send(actix::msgs::SystemExit(0)); // <- remove this line, this code stops system during testing
let _ = sys.run();
}
```
If `specialization` is enabled, conversion could be simplier:
```rust,ignore
impl Into<Result<HttpResponse>> for MyObj {
fn into(self) -> Result<HttpResponse> {
let body = serde_json::to_string(&self)?;
Ok(HttpResponse::Ok()
.content_type("application/json")
.body(body)?)
}
}
```
### Async handlers
There are two different types of async handlers.
Response object could be generated asynchronously. In this case handle must
return `Future` object that resolves to `HttpResponse`, i.e:
```rust,ignore
fn index(req: HttpRequest) -> Box<Future<HttpResponse, Error>> {
...
}
```
This handler can be registered with `ApplicationBuilder::async()` and
`Resource::async()` methods.
Or response body can be generated asynchronously. In this case body
must implement stream trait `Stream<Item=Bytes, Error=Error>`, i.e:
```rust,ignore
fn index(req: HttpRequest) -> HttpResponse {
let body: Box<Stream<Item=Bytes, Error=Error>> = Box::new(SomeStream::new());
HttpResponse::Ok().
.content_type("application/json")
.body(Body::Streaming(body)).unwrap()
}
```
Both methods could be combined. (i.e Async response with streaming body)