Genie.jl

The highly productive Julia web framework

View the Project on GitHub GenieFramework/Genie.jl

Advanced routing techniques

Genie’s router can be considered the brain of the app, matching web requests to functions, extracting and setting up the request’s variables and the execution environment, and invoking the response methods. Such power is accompanied by a powerful set of features for defining routes. Let’s dive into these.

Static routing

Starting with the simplest case, we can register “plain” routes by using the route method. The method takes as its required arguments the URI pattern and the function that should be invoked in order to provide the response. The router supports two ways of registering routes, either route(pattern::String, f::Function) or route(f::Function, pattern::String). The first syntax is for passing function references – while the second is for defining inline function.

Example

The following snippet defines a function greet which returns the “Welcome to Genie!” string. We use the function as our route handler, by passing it as the second argument to the route method.

using Genie, Genie.Router

greet() = "Welcome to Genie!"

route("/greet", greet)          # [GET] /greet => greet

up() # start the server

If you use your browser to navigate to http://127.0.0.1:8000/greet you’ll see the code in action.

However, defining a dedicated handler function might be overkill for simple cases like this. As such, Genie allows registering in-line handlers:

route("/bye") do
  "Good bye!"
end                 # [GET] /bye => getfield(Main, Symbol("##3#4"))()

You can just navigate to http://127.0.0.1:8000/bye – the route is instantly available in the app.


HEADS UP

The routes are added in the order in which they are defined but are matched from newest to oldest. This means that you can define a new route to overwrite a previously defined one.

Unlike Julia’s multiple dispatch, Genie’s router won’t match the most specific rule, but the first matching one. So if, for example, you register a route to match /*, it will handle all the requests, even if you have previously defined more specific routes. As a side-note, you can use this technique to temporarily divert all users to a maintenance page.


Dynamic routing (using route parameters)

Static routing works great for fixed URLs. But what if we have dynamic URLs, where the components map to information in the backend (like database IDs) and vary with each request? For example, how would we handle a URL like “/customers/57943/orders/458230”, where 57943 is the customer id and 458230 is the order id.

Such situations are handled through dynamic routing or route parameters. For the previous example, “/customers/57943/orders/458230”, we can define a dynamic route as “/customers/:customer_id/orders/:order_id”. Upon matching the request, the Router will unpack the values and expose them in the @params collection.

Example

using Genie, Genie.Router, Genie.Requests

route("/customers/:customer_id/orders/:order_id") do
  "You asked for the order $(payload(:order_id)) for customer $(payload(:customer_id))"
end

up()

Routing methods (GET, POST, PUT, PATCH, DELETE, OPTIONS)

By default, routes handle GET requests, since these are the most common. In order to define routes for handling other types of request methods, we need to pass the method keyword argument, indicating the HTTP method. Genie’s Router supports GET, POST, PUT, PATCH, DELETE, OPTIONS methods.

The router defines and exports constants for each of these as Router.GET, Router.POST, Router.PUT, Router.PATCH, Router.DELETE, and Router.OPTIONS.

Example

We can setup the following PATCH route:

using Genie, Genie.Router, Genie.Requests

route("/patch_stuff", method = PATCH) do
  "Stuff to patch"
end

up()

And we can test it using the HTTP package:

using HTTP

HTTP.request("PATCH", "http://127.0.0.1:8000/patch_stuff").body |> String
2019-08-19 14:23:46:INFO:Main: /patch_stuff 200

"Stuff to patch"

By sending a request with the PATCH method, our route is triggered. Consequently, we access the response body and convert it to a string, which is “Stuff to patch”, corresponding to our response.

Named routes

Genie allows tagging routes with names. This is a very powerful feature, to be used in conjunction with the Router.tolink method, for dynamically generating URLs towards the routes. The advantage of this technique is that if we refer the route by name and generate the links dynamically using tolink, as long as the name of the route stays the same, if we change the route pattern, all the URLs will automatically match the new route definiton.

In order to name a route we need to use the named keyword argument, which expects a Symbol.

Example

using Genie, Genie.Router, Genie.Requests

route("/customers/:customer_id/orders/:order_id", named = :get_customer_order) do
  "Looking up order $(payload(:order_id)) for customer  $(payload(:customer_id))"
end         #  [GET] /customers/:customer_id/orders/:order_id => getfield(Main, Symbol("##5#6"))()

We can check the status of our route with:

julia> @routes
OrderedCollections.OrderedDict{Symbol,Genie.Router.Route} with 1 entry:
  :get_customer_order => [GET] /customers/:customer_id/orders/:order_id => getfield(Main, Symbol("##5#6"))()

HEADS UP

For consistency, Genie names all the routes. However, the auto-generated name is state dependent. So, if you change the route, it’s possible that the name will change as well. Thus, it’s best to explicitly name the routes if you plan on referencing them throughout the app.


We can confirm this by adding an anonymous route:

route("/foo") do
  "foo"
end  #  [GET] /foo => getfield(Main, Symbol("##7#8"))()

julia> @routes
OrderedCollections.OrderedDict{Symbol,Genie.Router.Route} with 2 entries:
  :get_customer_order => [GET] /customers/:customer_id/orders/:order_id => getfield(Main, Symbol("##5#6"))()
  :get_foo            => [GET] /foo => getfield(Main, Symbol("##7#8"))()

The new route has been automatically named get_foo, based on the method and URI pattern.

We can use the name of the route to link back to it through the linkto method.

Example

Let’s start with the previously defined two routes:

julia> @routes
OrderedCollections.OrderedDict{Symbol,Genie.Router.Route} with 2 entries:
  :get_customer_order => [GET] /customers/:customer_id/orders/:order_id => getfield(Main, Symbol("##5#6"))()
  :get_foo            => [GET] /foo => getfield(Main, Symbol("##7#8"))()

Static routes such as :get_foo are straightforward to target:

julia> linkto(:get_foo)
"/foo"

For dynamic routes, it’s a bit more involved as we need to supply the values for each of the parameters, as keyword arguments:

julia> linkto(:get_customer_order, customer_id = 1234, order_id = 5678)
"/customers/1234/orders/5678"

The linkto should be used in conjunction with the HTML code for generating links, ie:

<a href="$(linkto(:get_foo))">Foo</a>

Listing routes

At any time we can check which routes are registered with Router.routes:

julia> routes()
2-element Array{Genie.Router.Route,1}:
 [GET] /foo => getfield(Main, Symbol("##7#8"))()
 [GET] /customers/:customer_id/orders/:order_id => getfield(Main, Symbol("##5#6"))()

Or, we can use the previously discussed @routes macro:

julia> @routes
OrderedCollections.OrderedDict{Symbol,Genie.Router.Route} with 2 entries:
  :get_customer_order => [GET] /customers/:customer_id/orders/:order_id => getfield(Main, Symbol("##5#6"))()
  :get_foo            => [GET] /foo => getfield(Main, Symbol("##7#8"))()

The Route type

The routes are represented internally by the Route type which has 4 fields:

Removing routes

We can delete routes from the stack by calling the delete! method and passing the collection of routes and the name of the route to be removed. The method returns the collection of (remaining) routes

Example

julia> @routes
OrderedCollections.OrderedDict{Symbol,Genie.Router.Route} with 2 entries:
  :get_customer_order => [GET] /customers/:customer_id/orders/:order_id => getfield(Main, Symbol("##3#4"))()
  :get_foo            => [GET] /foo => getfield(Main, Symbol("##9#10"))()

julia> Router.delete!(@routes, :get_foo)
OrderedCollections.OrderedDict{Symbol,Genie.Router.Route} with 1 entry:
  :get_customer_order => [GET] /customers/:customer_id/orders/:order_id => getfield(Main, Symbol("##3#4"))()

julia> @routes
OrderedCollections.OrderedDict{Symbol,Genie.Router.Route} with 1 entry:
  :get_customer_order => [GET] /customers/:customer_id/orders/:order_id => getfield(Main, Symbol("##3#4"))()

Matching routes by type of arguments

By default route parameters are parsed into the payload collection as SubString{String}:

using Genie, Genie.Router, Genie.Requests

route("/customers/:customer_id/orders/:order_id") do
  "Order ID has type $(payload(:order_id) |> typeof) // Customer ID has type $(payload(:customer_id) |> typeof)"
end

This will output Order ID has type SubString{String} // Customer ID has type SubString{String}

However, for such a case, we’d very much prefer to receive our data as Int to avoid an explicit conversion – and to match only numbers. Genie supports such a workflow by allowing type annotations to route parameters:

route("/customers/:customer_id::Int/orders/:order_id::Int", named = :get_customer_order) do
  "Order ID has type $(payload(:order_id) |> typeof) // Customer ID has type $(payload(:customer_id) |> typeof)"
end     #     [GET] /customers/:customer_id::Int/orders/:order_id::Int => getfield(Main, Symbol("##3#4"))()

Notice how we’ve added type annotations to :customer_id and :order_id in the form :customer_id::Int and :order_id::Int.

However, attempting to access the URL http://127.0.0.1:8000/customers/10/orders/20 will fail:

Failed to match URI params between Int64::DataType and 10::SubString{String}
MethodError(convert, (Int64, "10"), 0x00000000000063fe)
/customers/10/orders/20 404

As you can see, Genie attempts to convert the types from the default SubString{String} to Int – but doesn’t know how. It fails, can’t find other matching routes and returns a 404 Not Found response.

Type conversion in routes

The error is easy to address though: we need to provide a type converter from SubString{String} to Int.

Base.convert(::Type{Int}, v::SubString{String}) = parse(Int, v)

Once we register the converter in Base, our request will be correctly handled, resulting in Order ID has type Int64 // Customer ID has type Int64

Matching individual URI segments

Besides matching the full route, Genie also allows matching individual URI segments. That is, enforcing that the various route parameters obey a certain pattern. In order to introduce constraints for route parameters we append #pattern at the end of the route parameter.

Example

For instance, let’s assume that we want to implement a localized website where we have a URL structure like: mywebsite.com/en, mywebsite.com/es and mywebsite.com/de. We can define a dynamic route and extract the locale variable to serve localized content:

route(":locale", TranslationsController.index)

This will work very well, matching requests and passing the locale into our code within the payload(:locale) variable. However, it will also be too greedy, virtually matching all the requests, including things like static files (ie mywebsite.com/favicon.ico). We can constrain what the :locale variable can match, by appending the pattern (a regex pattern):

route(":locale#(en|es|de)", TranslationsController.index)

The refactored route only allows :locale to match one of en, es, and de strings.


HEADS UP

Keep in mind not to duplicate application logic. For instance, if you have an array of supported locales, you can use that to dynamically generate the pattern – routes can be fully dynamically generated!

const LOCALE = ":locale#($(join(TranslationsController.AVAILABLE_LOCALES, '|')))"

route("/$LOCALE", TranslationsController.index, named = :get_index)

The @params collection

It’s good to know that the router bundles all the parameters of the current request into the @params collection (a Dict{Symbol,Any}). This contains valuable information, such as route parameters, query params, POST payload, the original HTTP.Request and HTTP.Response objects, etcetera. In general it’s recommended not to access the @params collection directly but through the utility methods defined by Genie.Requests and Genie.Responses – but knowing about @params might come in handy for advanced users.