actix-web/guide/src/qs_7.md

# Request & Response

## Response

Builder-like patter is used to construct an instance of `HttpResponse`.
`HttpResponse` provides several method that returns `HttpResponseBuilder` instance,
which is implements various convenience methods that helps build response.
Check [documentation](../actix_web/dev/struct.HttpResponseBuilder.html)
for type description. Methods `.body`, `.finish`, `.json` finalizes response creation and
returns constructed *HttpResponse* instance. if this methods get called for the same
builder instance multiple times, builder will panic.

```rust
# extern crate actix_web;
use actix_web::*;
use actix_web::headers::ContentEncoding;

fn index(req: HttpRequest) -> HttpResponse {
    HttpResponse::Ok()
        .content_encoding(ContentEncoding::Br)
        .content_type("plain/text")
        .header("X-Hdr", "sample")
        .body("data").unwrap()
}
# fn main() {}
```

## Content encoding

Actix automatically *compress*/*decompress* payload. Following codecs are supported: 

 * Brotli
 * Gzip
 * Deflate
 * Identity
 
 If request headers contains `Content-Encoding` header, request payload get decompressed
 according to header value. Multiple codecs are not supported, i.e: `Content-Encoding: br, gzip`.
 
Response payload get compressed based on *content_encoding* parameter. 
By default `ContentEncoding::Auto` is used. If `ContentEncoding::Auto` is selected
then compression depends on request's `Accept-Encoding` header. 
`ContentEncoding::Identity` could be used to disable compression.
If other content encoding is selected the compression is enforced for this codec. For example,
to enable `brotli` response's body compression use `ContentEncoding::Br`:

```rust
# extern crate actix_web;
use actix_web::*;
use actix_web::headers::ContentEncoding;

fn index(req: HttpRequest) -> HttpResponse {
    HttpResponse::Ok()
        .content_encoding(ContentEncoding::Br)
        .body("data").unwrap()
}
# fn main() {}
```


## JSON Request

There are two options of json body deserialization. 

First option is to use *HttpResponse::json()* method. This method returns
[*JsonBody*](../actix_web/dev/struct.JsonBody.html) object which resolves into 
deserialized value.

```rust
# extern crate actix;
# extern crate actix_web;
# extern crate futures;
# extern crate serde_json;
# #[macro_use] extern crate serde_derive;
# use actix_web::*;
# use futures::Future;
#[derive(Debug, Serialize, Deserialize)]
struct MyObj {
    name: String,
    number: i32,
}

fn index(mut req: HttpRequest) -> Box<Future<Item=HttpResponse, Error=Error>> {
    req.json().from_err()
        .and_then(|val: MyObj| {
            println!("model: {:?}", val);
            Ok(httpcodes::HTTPOk.build().json(val)?)  // <- send response
        })
        .responder()
}
# fn main() {}
```

Or you can manually load payload into memory and then deserialize it.
Here is simple example. We will deserialize *MyObj* struct. We need to load request
body first and then deserialize json into object.

```rust
# extern crate actix_web;
# extern crate futures;
# use actix_web::*;
# #[macro_use] extern crate serde_derive;
extern crate serde_json;
use futures::{Future, Stream};

#[derive(Serialize, Deserialize)]
struct MyObj {name: String, number: i32}

fn index(mut req: HttpRequest) -> Box<Future<Item=HttpResponse, Error=Error>> {
   // `concat2` will asynchronously read each chunk of the request body and
   // return a single, concatenated, chunk
   req.payload_mut().readany().concat2()
      // `Future::from_err` acts like `?` in that it coerces the error type from
      // the future into the final error type
      .from_err()
      // `Future::and_then` can be used to merge an asynchronous workflow with a
      // synchronous workflow
      .and_then(|body| {                           // <- body is loaded, now we can deserialize json
          let obj = serde_json::from_slice::<MyObj>(&body)?;
          Ok(httpcodes::HTTPOk.build().json(obj)?) // <- send response
      })
      .responder()
}
# fn main() {}
```

Complete example for both options is available in 
[examples directory](https://github.com/actix/actix-web/tree/master/examples/json/).


## JSON Response

The `Json` type allows you to respond with well-formed JSON data: simply return a value of 
type Json<T> where T is the type of a structure to serialize into *JSON*. The 
type `T` must implement the `Serialize` trait from *serde*.

```rust
# extern crate actix_web;
#[macro_use] extern crate serde_derive;
use actix_web::*;

#[derive(Serialize)]
struct MyObj {
    name: String,
}

fn index(req: HttpRequest) -> Result<Json<MyObj>> {
    Ok(Json(MyObj{name: req.match_info().query("name")?}))
}

fn main() {
    Application::new()
        .resource(r"/a/{name}", |r| r.method(Method::GET).f(index))
        .finish();
}
```

## Chunked transfer encoding

Actix automatically decode *chunked* encoding. `HttpRequest::payload()` already contains
decoded bytes stream. If request payload compressed with one of supported
compression codecs (br, gzip, deflate) bytes stream get decompressed.

Chunked encoding on response could be enabled with `HttpResponseBuilder::chunked()` method.
But this takes effect only for `Body::Streaming(BodyStream)` or `Body::StreamingContext` bodies.
Also if response payload compression is enabled and streaming body is used, chunked encoding
get enabled automatically.

Enabling chunked encoding for *HTTP/2.0* responses is forbidden.

```rust
# extern crate actix_web;
use actix_web::*;

fn index(req: HttpRequest) -> HttpResponse {
    HttpResponse::Ok()
        .chunked()
        .body(Body::Streaming(payload::Payload::empty().stream())).unwrap()
}
# fn main() {}
```

## Multipart body

Actix provides multipart stream support. 
[*Multipart*](../actix_web/multipart/struct.Multipart.html) is implemented as 
a stream of multipart items, each item could be
[*Field*](../actix_web/multipart/struct.Field.html) or nested *Multipart* stream.
`HttpResponse::multipart()` method returns *Multipart* stream for current request.

In simple form multipart stream handling could be implemented similar to this example

```rust,ignore
# extern crate actix_web;
use actix_web::*;

fn index(req: HttpRequest) -> Box<Future<...>> {
    req.multipart()        // <- get multipart stream for current request
       .and_then(|item| {  // <- iterate over multipart items
           match item {
                           // Handle multipart Field
              multipart::MultipartItem::Field(field) => {
                 println!("==== FIELD ==== {:?} {:?}", field.headers(), field.content_type());
                 
                 Either::A(
                           // Field in turn is a stream of *Bytes* objects
                   field.map(|chunk| {
                        println!("-- CHUNK: \n{}",
                                 std::str::from_utf8(&chunk).unwrap());})
                      .fold((), |_, _| result(Ok(()))))
                },
              multipart::MultipartItem::Nested(mp) => {
                         // Or item could be nested Multipart stream 
                 Either::B(result(Ok(())))
              }
         }
   })
}
```

Full example is available in 
[examples directory](https://github.com/actix/actix-web/tree/master/examples/multipart/).

## Urlencoded body

Actix provides support for *application/x-www-form-urlencoded* encoded body.
`HttpResponse::urlencoded()` method returns
[*UrlEncoded*](../actix_web/dev/struct.UrlEncoded.html) future, it resolves 
into `HashMap<String, String>` which contains decoded parameters.
*UrlEncoded* future can resolve into a error in several cases:

* content type is not `application/x-www-form-urlencoded`
* transfer encoding is `chunked`.
* content-length is greater than 256k
* payload terminates with error.


```rust
# extern crate actix_web;
# extern crate futures;
use actix_web::*;
use futures::future::{Future, ok};

fn index(mut req: HttpRequest) -> Box<Future<Item=HttpResponse, Error=Error>> {
    req.urlencoded()         // <- get UrlEncoded future
       .from_err()
       .and_then(|params| {  // <- url encoded parameters
             println!("==== BODY ==== {:?}", params);
             ok(httpcodes::HTTPOk.into())
       })
       .responder()
}
# fn main() {}
```


## Streaming request

Actix uses [*Payload*](../actix_web/payload/struct.Payload.html) object as request payload stream.
*HttpRequest* provides several methods, which can be used for payload access.
At the same time *Payload* implements *Stream* trait, so it could be used with various
stream combinators. Also *Payload* provides several convenience methods that return
future object that resolve to Bytes object.

* *readany()* method returns *Stream* of *Bytes* objects.

* *readexactly()* method returns *Future* that resolves when specified number of bytes
  get received.
  
* *readline()* method returns *Future* that resolves when `\n` get received.

* *readuntil()* method returns *Future* that resolves when specified bytes string
  matches in input bytes stream

In this example handle reads request payload chunk by chunk and prints every chunk.

```rust
# extern crate actix_web;
# extern crate futures;
# use futures::future::result;
use actix_web::*;
use futures::{Future, Stream};


fn index(mut req: HttpRequest) -> Box<Future<Item=HttpResponse, Error=Error>> {
    req.payload()
       .readany()
       .from_err()
       .fold((), |_, chunk| {
            println!("Chunk: {:?}", chunk);
            result::<_, error::PayloadError>(Ok(()))
        })
       .map(|_| HttpResponse::Ok().finish().unwrap())
       .responder()
}
# fn main() {}
```