actix-website/content/docs/response.md

title	menu	weight
Responses	docs_advanced	210

Response

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.

Check the documentation for type descriptions.

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.

{{< include-example example="responses" file="main.rs" section="builder" >}}

JSON Response

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.

For the following example to work, you need to add serde to your dependencies in Cargo.toml:

[dependencies]
serde = "1"

{{< include-example example="responses" file="json_resp.rs" section="json-resp" >}}

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.

Content encoding

Actix-web can automatically compress payloads with the Compress middleware. The following codecs are supported:

• Brotli
• Gzip
• Deflate
• Identity

{{< include-example example="responses" file="compress.rs" section="compress" >}}

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.

ContentEncoding::Identity can be used to disable compression. If another content encoding is selected, the compression is enforced for that codec.

For example, to enable brotli for a single handler use ContentEncoding::Br:

{{< include-example example="responses" file="brotli.rs" section="brotli" >}}

or for the entire application:

{{< include-example example="responses" file="brotli_two.rs" section="brotli-two" >}}

In this case we explicitly disable content compression by setting content encoding to an Identity value:

{{< include-example example="responses" file="identity.rs" section="identity" >}}

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:

{{< include-example example="responses" file="identity_two.rs" section="identity-two" >}}

Also it is possible to set default content encoding on application level, by default ContentEncoding::Auto is used, which implies automatic content compression negotiation.

{{< include-example example="responses" file="auto.rs" section="auto" >}}