URL Dispatch

URL Dispatch

URL dispatch provides a simple way for mapping URLs to Handler code using a simple pattern matching language. If one of the patterns matches the path information associated with a request, a particular handler object is invoked.

A handler is a specific object that implements the Handler trait, defined in your application, that receives the request and returns a response object. More information is available in the handler section.

Resource configuration

Resource configuration is the act of adding a new resources to an application. A resource has a name, which acts as an identifier to be used for URL generation. The name also allows developers to add routes to existing resources. A resource also has a pattern, meant to match against the PATH portion of a URL (the portion following the scheme and port, e.g. /foo/bar in the URL http://localhost:8080/foo/bar?q=value). It does not match against the QUERY portion (the portion that follows ?, e.g. q=value in http://localhost:8080/foo/bar?q=value).

The App::route() method provides simple way of registering routes. This method adds a single route to application routing table. This method accepts a path pattern, http method and a handler function. route() method could be called multiple times for the same path, in that case, multiple routes register for the same resource path.

use actix_web::{http::Method, App, HttpRequest, HttpResponse};

fn index(req: HttpRequest) -> HttpResponse {
    unimplemented!()
}

fn main() {
    App::new()
        .route("/user/{name}", Method::GET, index)
        .route("/user/{name}", Method::POST, index)
        .finish();
}

While App::route() provides simple way of registering routes, to access complete resource configuration, a different method has to be used. The App::resource() method adds a single resource to application routing table. This method accepts a path pattern and a resource configuration function.

use actix_web::{http::Method, App, HttpRequest, HttpResponse};

fn index(req: &HttpRequest) -> HttpResponse {
    unimplemented!()
}

fn main() {
    App::new()
        .resource("/prefix", |r| r.f(index))
        .resource("/user/{name}", |r| {
            r.method(Method::GET).f(|req| HttpResponse::Ok())
        })
        .finish();
}

The Configuration function has the following type:

FnOnce(&mut Resource<_>) -> ()

The Configuration function can set a name and register specific routes. If a resource does not contain any route or does not have any matching routes, it returns NOT FOUND http response.

Configuring a Route

Resource contains a set of routes. Each route in turn has a set of predicates and a handler. New routes can be created with Resource::route() method which returns a reference to new Route instance. By default the route does not contain any predicates, so matches all requests and the default handler is HttpNotFound.

The application routes incoming requests based on route criteria which are defined during resource registration and route registration. Resource matches all routes it contains in the order the routes were registered via Resource::route().

A Route can contain any number of predicates but only one handler.

use actix_web::{pred, App, HttpResponse};

fn main() {
    App::new()
        .resource("/path", |resource| {
            resource
                .route()
                .filter(pred::Get())
                .filter(pred::Header("content-type", "text/plain"))
                .f(|req| HttpResponse::Ok())
        })
        .finish();
}

In this example, HttpResponse::Ok() is returned for GET requests. If a request contains Content-Type header, the value of this header is text/plain, and path equals to /path, Resource calls handle of the first matching route.

If a resource can not match any route, a “NOT FOUND” response is returned.

ResourceHandler::route() returns a Route object. Route can be configured with a builder-like pattern. Following configuration methods are available:

  • Route::filter() registers a new predicate. Any number of predicates can be registered for each route.
  • Route::f() registers handler function for this route. Only one handler can be registered. Usually handler registration is the last config operation. Handler function can be a function or closure and has the type Fn(&HttpRequest<S>) -> R + 'static
  • Route::h() registers a handler object that implements the Handler trait. This is similar to f() method - only one handler can be registered. Handler registration is the last config operation.
  • Route::a() registers an async handler function for this route. Only one handler can be registered. Handler registration is the last config operation. Handler function can be a function or closure and has the type Fn(&HttpRequest<S>) -> Future<Item = HttpResponse, Error = Error> + 'static

Route matching

The main purpose of route configuration is to match (or not match) the request’s path against a URL path pattern. path represents the path portion of the URL that was requested.

The way that actix does this is very simple. When a request enters the system, for each resource configuration declaration present in the system, actix checks the request’s path against the pattern declared. This checking happens in the order that the routes were declared via App::resource() method. If resource can not be found, the default resource is used as the matched resource.

When a route configuration is declared, it may contain route predicate arguments. All route predicates associated with a route declaration must be true for the route configuration to be used for a given request during a check. If any predicate in the set of route predicate arguments provided to a route configuration returns false during a check, that route is skipped and route matching continues through the ordered set of routes.

If any route matches, the route matching process stops and the handler associated with the route is invoked. If no route matches after all route patterns are exhausted, a NOT FOUND response get returned.

Resource pattern syntax

The syntax of the pattern matching language used by actix in the pattern argument is straightforward.

The pattern used in route configuration may start with a slash character. If the pattern does not start with a slash character, an implicit slash will be prepended to it at matching time. For example, the following patterns are equivalent:

{foo}/bar/baz

and:

/{foo}/bar/baz

A variable part (replacement marker) is specified in the form {identifier}, where this means “accept any characters up to the next slash character and use this as the name in the HttpRequest.match_info() object”.

A replacement marker in a pattern matches the regular expression [^{}/]+.

A match_info is the Params object representing the dynamic parts extracted from a URL based on the routing pattern. It is available as request.match_info. For example, the following pattern defines one literal segment (foo) and two replacement markers (baz, and bar):

foo/{baz}/{bar}

The above pattern will match these URLs, generating the following match information:

foo/1/2        -> Params {'baz':'1', 'bar':'2'}
foo/abc/def    -> Params {'baz':'abc', 'bar':'def'}

It will not match the following patterns however:

foo/1/2/        -> No match (trailing slash)
bar/abc/def     -> First segment literal mismatch

The match for a segment replacement marker in a segment will be done only up to the first non-alphanumeric character in the segment in the pattern. So, for instance, if this route pattern was used:

foo/{name}.html

The literal path /foo/biz.html will match the above route pattern, and the match result will be Params{'name': 'biz'}. However, the literal path /foo/biz will not match, because it does not contain a literal .html at the end of the segment represented by {name}.html (it only contains biz, not biz.html).

To capture both segments, two replacement markers can be used:

foo/{name}.{ext}

The literal path /foo/biz.html will match the above route pattern, and the match result will be Params{‘name’: ‘biz’, ‘ext’: ‘html’}. This occurs because there is a literal part of . (period) between the two replacement markers {name} and {ext}.

Replacement markers can optionally specify a regular expression which will be used to decide whether a path segment should match the marker. To specify that a replacement marker should match only a specific set of characters as defined by a regular expression, you must use a slightly extended form of replacement marker syntax. Within braces, the replacement marker name must be followed by a colon, then directly thereafter, the regular expression. The default regular expression associated with a replacement marker [^/]+ matches one or more characters which are not a slash. For example, under the hood, the replacement marker {foo} can more verbosely be spelled as {foo:[^/]+}. You can change this to be an arbitrary regular expression to match an arbitrary sequence of characters, such as {foo:\d+} to match only digits.

Segments must contain at least one character in order to match a segment replacement marker. For example, for the URL /abc/:

  • /abc/{foo} will not match.
  • /{foo}/ will match.

Note: path will be URL-unquoted and decoded into valid unicode string before matching pattern and values representing matched path segments will be URL-unquoted too.

So for instance, the following pattern:

foo/{bar}

When matching the following URL:

http://example.com/foo/La%20Pe%C3%B1a

The matchdict will look like so (the value is URL-decoded):

Params{'bar': 'La Pe\xf1a'}

Literal strings in the path segment should represent the decoded value of the path provided to actix. You don’t want to use a URL-encoded value in the pattern. For example, rather than this:

/Foo%20Bar/{baz}

You’ll want to use something like this:

/Foo Bar/{baz}

It is possible to get “tail match”. For this purpose custom regex has to be used.

foo/{bar}/{tail:.*}

The above pattern will match these URLs, generating the following match information:

foo/1/2/           -> Params{'bar':'1', 'tail': '2/'}
foo/abc/def/a/b/c  -> Params{'bar':u'abc', 'tail': 'def/a/b/c'}

Scoping Routes

Scoping helps you organize routes sharing common root paths. You can nest scopes within scopes.

Suppose that you want to organize paths to endpoints used to manage a “Project”, consisting of “Tasks”. Such paths may include:

  • /project
  • /project/{project_id}
  • /project/{project_id}/task
  • /project/{project_id}/task/{task_id}

A scoped layout of these paths would appear as follows

App::new().scope("/project", |proj_scope| {
    proj_scope
        .resource("", |r| {
            r.method(Method::GET).f(get_projects);
            r.method(Method::POST).f(create_project)
        })
        .resource("/{project_id}", |r| {
            r.method(Method::PUT).with(update_project);
            r.method(Method::DELETE).f(delete_project)
        })
        .nested("/{project_id}/task", |task_scope| {
            task_scope
                .resource("", |r| {
                    r.method(Method::GET).f(get_tasks);
                    r.method(Method::POST).f(create_task)
                })
                .resource("/{task_id}", |r| {
                    r.method(Method::PUT).with(update_task);
                    r.method(Method::DELETE).with(delete_task)
                })
        })
});

A scoped path can contain variable path segments as resources. Consistent with unscoped paths.

You can get variable path segments from HttpRequest::match_info(). Path extractor also is able to extract scope level variable segments.

Match information

All values representing matched path segments are available in HttpRequest::match_info. Specific values can be retrieved with Params::get().

Any matched parameter can be deserialized into a specific type if the type implements the FromParam trait. For example most standard integer types the trait, i.e.:

use actix_web::{App, HttpRequest, Result};

fn index(req: &HttpRequest) -> Result<String> {
    let v1: u8 = req.match_info().query("v1")?;
    let v2: u8 = req.match_info().query("v2")?;
    Ok(format!("Values {} {}", v1, v2))
}

fn main() {
    App::new()
        .resource(r"/a/{v1}/{v2}/", |r| r.f(index))
        .finish();
}

For this example for path ‘/a/1/2/’, values v1 and v2 will resolve to “1” and “2”.

It is possible to create a PathBuf from a tail path parameter. The returned PathBuf is percent-decoded. If a segment is equal to “..”, the previous segment (if any) is skipped.

For security purposes, if a segment meets any of the following conditions, an Err is returned indicating the condition met:

  • Decoded segment starts with any of: . (except ..), *
  • Decoded segment ends with any of: :, >, <
  • Decoded segment contains any of: /
  • On Windows, decoded segment contains any of: ‘\’
  • Percent-encoding results in invalid UTF8.

As a result of these conditions, a PathBuf parsed from request path parameter is safe to interpolate within, or use as a suffix of, a path without additional checks.

use actix_web::{http::Method, App, HttpRequest, Result};
use std::path::PathBuf;

fn index(req: &HttpRequest) -> Result<String> {
    let path: PathBuf = req.match_info().query("tail")?;
    Ok(format!("Path {:?}", path))
}

fn main() {
    App::new()
        .resource(r"/a/{tail:.*}", |r| r.method(Method::GET).f(index))
        .finish();
}

List of FromParam implementations can be found in api docs

Path information extractor

Actix provides functionality for type safe path information extraction. Path extracts information, destination type could be defined in several different forms. Simplest approach is to use tuple type. Each element in tuple must correpond to one element from path pattern. i.e. you can match path pattern /{id}/{username}/ against Path<(u32, String)> type, but Path<(String, String, String)> type will always fail.

use actix_web::{http::Method, App, Path, Result};

// extract path info using serde
fn index(info: Path<(String, u32)>) -> Result<String> {
    Ok(format!("Welcome {}! id: {}", info.0, info.1))
}

fn main() {
    let app = App::new().resource(
        "/{username}/{id}/index.html", // <- define path parameters
        |r| r.method(Method::GET).with(index),
    );
}

It also possible to extract path pattern information to a struct. In this case, this struct must implement *serde’s *Deserialize trait.

extern crate serde_derive;
use actix_web::{http::Method, App, Path, Result};

#[derive(Deserialize)]
struct Info {
    username: String,
}

// extract path info using serde
fn index(info: Path<Info>) -> Result<String> {
    Ok(format!("Welcome {}!", info.username))
}

fn main() {
    let app = App::new().resource(
        "/{username}/index.html", // <- define path parameters
        |r| r.method(Method::GET).with(index),
    );
}

Query provides similar functionality for request query parameters.

Generating resource URLs

Use the HttpRequest.url_for() method to generate URLs based on resource patterns. For example, if you’ve configured a resource with the name “foo” and the pattern “{a}/{b}/{c}”, you might do this:

use actix_web::{http::header, http::Method, App, HttpRequest, HttpResponse, Result};

fn index(req: HttpRequest) -> Result<HttpResponse> {
    let url = req.url_for("foo", &["1", "2", "3"])?; // <- generate url for "foo" resource
    Ok(HttpResponse::Found()
        .header(header::LOCATION, url.as_str())
        .finish())
}

fn main() {
    let app = App::new()
        .resource("/test/{a}/{b}/{c}", |r| {
            r.name("foo"); // <- set resource name, then it could be used in `url_for`
            r.method(Method::GET).f(|_| HttpResponse::Ok());
        })
        .route("/test/", Method::GET, index)
        .finish();
}

This would return something like the string http://example.com/test/1/2/3 (at least if the current protocol and hostname implied http://example.com). url_for() method returns Url object so you can modify this url (add query parameters, anchor, etc). url_for() could be called only for named resources otherwise error get returned.

External resources

Resources that are valid URLs, can be registered as external resources. They are useful for URL generation purposes only and are never considered for matching at request time.

use actix_web::{App, Error, HttpRequest, HttpResponse};

fn index(req: &HttpRequest) -> Result<HttpResponse, Error> {
    let url = req.url_for("youtube", &["oHg5SJYRHA0"])?;
    assert_eq!(url.as_str(), "https://youtube.com/watch/oHg5SJYRHA0");
    Ok(HttpResponse::Ok().into())
}

fn main() {
    let app = App::new()
        .resource("/index.html", |r| r.f(index))
        .external_resource("youtube", "https://youtube.com/watch/{video_id}")
        .finish();
}

Path normalization and redirecting to slash-appended routes

By normalizing it means:

  • To add a trailing slash to the path.
  • To replace multiple slashes with one.

The handler returns as soon as it finds a path that resolves correctly. The order of normalization conditions, if all are enabled, is 1) merge, 2) both merge and append and 3) append. If the path resolves with at least one of those conditions, it will redirect to the new path.

If append is true, append slash when needed. If a resource is defined with trailing slash and the request doesn’t have one, it will be appended automatically.

If merge is true, merge multiple consecutive slashes in the path into one.

This handler designed to be used as a handler for application’s default resource.

use actix_web::{http::NormalizePath, App};

fn main() {
    let app = App::new()
        .resource("/resource/", |r| r.f(index))
        .default_resource(|r| r.h(NormalizePath::default()))
        .finish();
}

In this example /resource, //resource/// will be redirected to /resource/.

In this example, the path normalization handler is registered for all methods, but you should not rely on this mechanism to redirect POST requests. The redirect of the slash-appending Not Found will turn a POST request into a GET, losing any POST data in the original request.

It is possible to register path normalization only for GET requests only:

use actix_web::{http::Method, http::NormalizePath, App};

fn main() {
    let app = App::new()
        .resource("/resource/", |r| r.f(index))
        .default_resource(|r| r.method(Method::GET).h(NormalizePath::default()))
        .finish();
}

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:

fn show_users(req: &HttpRequest) -> HttpResponse {
    unimplemented!()
}

fn main() {
    App::new()
        .prefix("/users")
        .resource("/show", |r| r.f(show_users))
        .finish();
}

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.

Custom route predicates

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 trait. Actix provides several predicates, you can check functions section of api docs.

Here is a simple predicate that check that a request contains a specific header:

use actix_web::{http, server::Request, pred::Predicate, App, HttpResponse};

struct ContentTypeHeader;

impl<S: 'static> Predicate<S> for ContentTypeHeader {
    fn check(&self, req: &Request, state: &S) -> bool {
        req.headers().contains_key(http::header::CONTENT_TYPE)
    }
}

fn main() {
    App::new().resource("/index.html", |r| {
        r.route()
            .filter(ContentTypeHeader)
            .f(|_| HttpResponse::Ok())
    });
}

In this example, index handler will be called only if request contains CONTENT-TYPE header.

Predicates have access to the application’s state via HttpRequest::state(). Also predicates can store extra information in request extensions.

Modifying predicate values

You can invert the meaning of any predicate value by wrapping it in a Not predicate. For example, if you want to return “METHOD NOT ALLOWED” response for all methods except “GET”:

use actix_web::{pred, App, HttpResponse};

fn main() {
    App::new()
        .resource("/index.html", |r| {
            r.route()
                .filter(pred::Not(pred::Get()))
                .f(|req| HttpResponse::MethodNotAllowed())
        })
        .finish();
}

The Any predicate accepts a list of predicates and matches if any of the supplied predicates match. i.e:

pred::Any(pred::Get()).or(pred::Post())

The All predicate accepts a list of predicates and matches if all of the supplied predicates match. i.e:

pred::All(pred::Get()).and(pred::Header("content-type", "plain/text"))

Changing the default Not Found response

If the path pattern can not be found in the routing table or a resource can not find matching route, the default resource is used. The default response is NOT FOUND. It is possible to override the NOT FOUND response with App::default_resource(). This method accepts a configuration function same as normal resource configuration with App::resource() method.

use actix_web::{http::Method, pred, App, HttpResponse};

fn main() {
    App::new()
        .default_resource(|r| {
            r.method(Method::GET).f(|req| HttpResponse::NotFound());
            r.route()
                .filter(pred::Not(pred::Get()))
                .f(|req| HttpResponse::MethodNotAllowed());
        })
        .finish();
}
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