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80 lines
2.6 KiB
Markdown
80 lines
2.6 KiB
Markdown
---
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title: Handlers
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menu: docs_basics
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weight: 160
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---
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# Request Handlers
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A request handler is an async function that accepts zero or more parameters that can be extracted
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from a request (ie, [*impl FromRequest*][implfromrequest]) and returns a type that can
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be converted into an HttpResponse (ie, [*impl Responder*][respondertrait]).
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Request handling happens in two stages. First the handler object is called, returning any
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object that implements the [*Responder*][respondertrait] trait. Then, `respond_to()` is
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called on the returned object, converting itself to a `HttpResponse` or `Error`.
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By default actix-web provides `Responder` implementations for some standard types,
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such as `&'static str`, `String`, etc.
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> For a complete list of implementations, check [*Responder documentation*][responderimpls].
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Examples of valid handlers:
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```rust
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async fn index(_req: HttpRequest) -> &'static str {
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"Hello world!"
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}
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```
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```rust
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async fn index(_req: HttpRequest) -> String {
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"Hello world!".to_owned()
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}
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```
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You can also change the signature to return `impl Responder` which works well if more
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complex types are involved.
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```rust
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async fn index(_req: HttpRequest) -> impl Responder {
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Bytes::from_static(b"Hello world!")
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}
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```
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```rust
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async fn index(req: HttpRequest) -> Box<Future<Item=HttpResponse, Error=Error>> {
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...
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}
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```
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## Response with custom type
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To return a custom type directly from a handler function, the type needs to implement the `Responder` trait.
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Let's create a response for a custom type that serializes to an `application/json` response:
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{{< include-example example="responder-trait" file="main.rs" section="responder-trait" >}}
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## Streaming response body
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Response body can be generated asynchronously. In this case, body must implement
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the stream trait `Stream<Item=Bytes, Error=Error>`, i.e:
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{{< include-example example="async-handlers" file="stream.rs" section="stream" >}}
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## Different return types (Either)
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Sometimes, you need to return different types of responses. For example, you can error
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check and return errors, return async responses, or any result that requires two different types.
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For this case, the [*Either*][either] type can be used. `Either` allows combining two
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different responder types into a single type.
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{{< include-example example="either" file="main.rs" section="either" >}}
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[implfromrequest]: https://docs.rs/actix-web/2/actix_web/trait.FromRequest.html
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[respondertrait]: https://docs.rs/actix-web/2/actix_web/trait.Responder.html
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[responderimpls]: https://docs.rs/actix-web/2/actix_web/trait.Responder.html#foreign-impls
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[either]: https://docs.rs/actix-web/2/actix_web/enum.Either.html
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