mirror of
https://github.com/actix/actix-website
synced 2024-11-24 08:43:01 +01:00
108 lines
5.1 KiB
Markdown
108 lines
5.1 KiB
Markdown
---
|
|
title: Application
|
|
menu: docs_basics
|
|
weight: 140
|
|
---
|
|
|
|
# Writing an Application
|
|
|
|
`actix-web` provides various primitives to build web servers and applications with Rust.
|
|
It provides routing, middlewares, pre-processing of requests, post-processing of responses,
|
|
websocket protocol handling, multipart streams, etc.
|
|
|
|
All actix web servers are built around the `App` instance. It is used for
|
|
registering routes for resources and middlewares. It also stores application
|
|
state shared across all handlers within same application.
|
|
|
|
Applications act as a namespace for all routes, i.e all routes for a specific application
|
|
have the same url path prefix. The application prefix always contains a leading "/" slash.
|
|
If a supplied prefix does not contain leading slash, it is automatically inserted.
|
|
The prefix should consist of value path segments.
|
|
|
|
> For an application with prefix `/app`,
|
|
> any request with the paths `/app`, `/app/`, or `/app/test` would match;
|
|
> however, the path `/application` would not match.
|
|
|
|
{{< include-example example="application" section="make_app" >}}
|
|
|
|
In this example, an application with the `/app` prefix and a `index.html` resource
|
|
are created. This resource is available through the `/app/index.html` url.
|
|
|
|
> For more information, check the
|
|
> [URL Dispatch](./sec-6-url-dispatch.html#using-a-application-prefix-to-compose-applications) section.
|
|
|
|
Multiple applications can be served with one server:
|
|
|
|
{{< include-example example="application" section="run_server" >}}
|
|
|
|
All `/app1` requests route to the first application, `/app2` to the second, and all other to the third.
|
|
**Applications get matched based on registration order**. If an application with a more generic
|
|
prefix is registered before a less generic one, it would effectively block the less generic
|
|
application matching. For example, if an `App` with the prefix `"/"` was registered
|
|
as the first application, it would match all incoming requests.
|
|
|
|
## State
|
|
|
|
Application state is shared with all routes and resources within the same application.
|
|
When using an http actor,state can be accessed with the `HttpRequest::state()` as read-only,
|
|
but interior mutability with `RefCell` can be used to achieve state mutability.
|
|
State is also available for route matching predicates and middlewares.
|
|
|
|
Let's write a simple application that uses shared state. We are going to store request count
|
|
in the state:
|
|
|
|
{{< include-example example="application" file="state.rs" section="setup" >}}
|
|
|
|
When the app is initialized it needs to be passed the initial state:
|
|
|
|
{{< include-example example="application" file="state.rs" section="make_app" >}}
|
|
|
|
> **Note**: http server accepts an application factory rather than an application
|
|
> instance. Http server constructs an application instance for each thread, thus application state
|
|
> must be constructed multiple times. If you want to share state between different threads, a
|
|
> shared object should be used, e.g. `Arc`. Application state does not need to be `Send` and `Sync`,
|
|
> but the application factory must be `Send` + `Sync`.
|
|
|
|
## Combining applications with different state
|
|
|
|
Combining multiple applications with different state is possible as well.
|
|
|
|
[server::new](https://docs.rs/actix-web/*/actix_web/server/fn.new.html) requires the handler to have a single type.
|
|
|
|
This limitation can easily be overcome with the [App::boxed](https://docs.rs/actix-web/*/actix_web/struct.App.html#method.boxed) method, which converts an App into a boxed trait object.
|
|
|
|
{{< include-example example="application" file="state.rs" section="combine" >}}
|
|
|
|
## Using an Application Prefix to Compose Applications
|
|
|
|
The `App::prefix()` method allows to set a specific application prefix.
|
|
This prefix represents a resource prefix that will be prepended to all resource patterns added
|
|
by the resource configuration. This can be used to help mount a set of routes at a different
|
|
location than the included callable's author intended while still maintaining the same
|
|
resource names.
|
|
|
|
For example:
|
|
|
|
{{< include-example example="url-dispatch" file="prefix.rs" section="prefix" >}}
|
|
|
|
In the above example, the *show_users* route will have an effective route pattern of
|
|
*/users/show* instead of */show* because the application's prefix argument will be prepended
|
|
to the pattern. The route will then only match if the URL path is */users/show*,
|
|
and when the `HttpRequest.url_for()` function is called with the route name show_users,
|
|
it will generate a URL with that same path.
|
|
|
|
## Application predicates and virtual hosting
|
|
|
|
You can think of a predicate as a simple function that accepts a *request* object reference
|
|
and returns *true* or *false*. Formally, a predicate is any object that implements the
|
|
[`Predicate`](../actix_web/pred/trait.Predicate.html) trait. Actix provides
|
|
several predicates, you can check
|
|
[functions section](../../actix-web/actix_web/pred/index.html#functions) of api docs.
|
|
|
|
Any of this predicates could be used
|
|
with [`App::filter()`](../actix_web/struct.App.html#method.filter) method. One of the
|
|
provided predicates is [`Host`](../actix_web/pred/fn.Host.html), it can be used
|
|
as application's filter based on request's host information.
|
|
|
|
{{< include-example example="application" file="vh.rs" section="vh" >}}
|