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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 request handler is a function that accepts zero or more parameters that can be extracted from a request (i.e., impl FromRequest) and returns a type that can be converted into an HttpResponse (i.e., impl Responder). 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.


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


In this example, HttpResponse::Ok() is returned for GET requests if the request contains Content-Type header, the value of this header is text/plain, and path equals to /path.

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::guard() registers a new guard. Any number of guards can be registered for each route.
  • Route::method() registers a method guard. Any number of guards can be registered for each route.
  • Route::to() registers an async handler function for this route. Only one handler can be registered. Usually handler registration is the last config operation.

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-web 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::service() 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 guard arguments. All route guards associated with a route declaration must be true for the route configuration to be used for a given request during a check. If any guard in the set of route guard 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 matchinfo 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 match dictionary 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': '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 view "Users". Such paths may include:

  • /users
  • /users/show
  • /users/show/{id}

A scoped layout of these paths would appear as follows


A scoped path can contain variable path segments as resources. Consistent with un-scoped 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 Path::get().


For this example for path '/a/1/2/', values v1 and v2 will resolve to "1" and "2".

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 correspond 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.


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


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:


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.


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.


In this example //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:


Using an Application Prefix to Compose Applications​

The web::scope() method allows to set a specific application scope. This scope 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:


In the above example, the show_users route will have an effective route pattern of /users/show instead of /show because the application's scope 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 guard​

You can think of a guard as a simple function that accepts a request object reference and returns true or false. Formally, a guard is any object that implements the Guard trait. Actix provides several predicates, you can check functions section of API docs.

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


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

Guards can not access or modify the request object, but it is possible to store extra information in request extensions.

Modifying guard 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":


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

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

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

guard::All(guard::Get()).and(guard::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_service(). This method accepts a configuration function same as normal resource configuration with App::service() method.