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69 lines
3.2 KiB
Markdown
69 lines
3.2 KiB
Markdown
---
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title: Responses
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menu: docs_advanced
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weight: 210
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---
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# Response
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A builder-like pattern is used to construct an instance of `HttpResponse`. `HttpResponse` provides several methods that return a `HttpResponseBuilder` instance, which implements various convenience methods for building responses.
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> Check the [documentation][responsebuilder] for type descriptions.
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The methods `.body`, `.finish`, and `.json` finalize response creation and return a constructed _HttpResponse_ instance. If this methods is called on the same builder instance multiple times, the builder will panic.
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{{< include-example example="responses" file="main.rs" section="builder" >}}
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# JSON Response
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The `Json` type allows 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_.
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For the following example to work, you need to add `serde` to your dependencies in `Cargo.toml`:
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```toml
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[dependencies]
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serde = "1"
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```
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{{< include-example example="responses" file="json_resp.rs" section="json-resp" >}}
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Using the `Json` type this way instead of calling the `.json` method on a `HttpResponse` makes it immediately clear that the function returns JSON and not any other type of response.
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# Content encoding
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Actix-web can automatically _compress_ payloads with the [_Compress middleware_][compressmidddleware]. The following codecs are supported:
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- Brotli
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- Gzip
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- Deflate
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- Identity
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{{< include-example example="responses" file="compress.rs" section="compress" >}}
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Response payload is compressed based on the _encoding_ parameter from the `middleware::BodyEncoding` trait. By default, `ContentEncoding::Auto` is used. If `ContentEncoding::Auto` is selected, then the compression depends on the request's `Accept-Encoding` header.
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> `ContentEncoding::Identity` can be used to disable compression. If another content encoding is selected, the compression is enforced for that codec.
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For example, to enable `brotli` for a single handler use `ContentEncoding::Br`:
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{{< include-example example="responses" file="brotli.rs" section="brotli" >}}
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or for the entire application:
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{{< include-example example="responses" file="brotli_two.rs" section="brotli-two" >}}
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In this case we explicitly disable content compression by setting content encoding to an `Identity` value:
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{{< include-example example="responses" file="identity.rs" section="identity" >}}
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When dealing with an already compressed body (for example when serving assets), set the content encoding to `Identity` to avoid compressing the already compressed data and set the `content-encoding` header manually:
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{{< include-example example="responses" file="identity_two.rs" section="identity-two" >}}
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Also it is possible to set default content encoding on application level, by default `ContentEncoding::Auto` is used, which implies automatic content compression negotiation.
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{{< include-example example="responses" file="auto.rs" section="auto" >}}
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[responsebuilder]: https://docs.rs/actix-web/3/actix_web/dev/struct.HttpResponseBuilder.html
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[compressmidddleware]: https://docs.rs/actix-web/3/actix_web/middleware/struct.Compress.html
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