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https://github.com/weavejester/ataraxy

A data-driven Ring routing and destructuring library
https://github.com/weavejester/ataraxy

clojure data-driven ring routing

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A data-driven Ring routing and destructuring library

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# Ataraxy



[![Build Status](https://travis-ci.org/weavejester/ataraxy.svg?branch=master)](https://travis-ci.org/weavejester/ataraxy)



A data-driven routing and destructuring library for [Ring][]. This

library is still being developed, so some functionality may change

before we hit version 1.0.0.



[ring]: https://github.com/ring-clojure/ring



## Rationale



There are several data-driven routing libraries for Ring, such as

[bidi][], [Silk][] and [gudu][]. Ataraxy differs from them because

it not only seeks to match a route, it also destructures the

incoming request.



In this sense it is similar to [Compojure][], in that the idea is to

remove extraneous information. However, while Compojure is designed to

use chains of functions, Ataraxy defines its functionality through a

declarative data structure.



[bidi]: https://github.com/juxt/bidi

[silk]: https://github.com/DomKM/silk

[gudu]: https://github.com/thatismatt/gudu

[compojure]: https://github.com/weavejester/compojure



## Example



```clojure

{["/api" {uid :identity}]

 {"/products"

   {[:get]                [:products/list uid]

    [:get "/" pid]        [:products/get uid ^uuid pid]

    [:get "/search" #{q}] [:products/search uid q]

    [:post {body :body}]  [:products/new uid body]}}}

```



## Installation



Add the following dependency to your `project.clj` file:



    [ataraxy "0.4.3"]



## Routing



Ataraxy uses a data structure to tell it how to route and destructure

requests. See the following section on [syntax](#syntax) for details.



```clojure

(def routes '{"/foo" [:foo]})

```



We can match a request map to a result with `matches`:



```clojure

(require '[ataraxy.core :as ataraxy])



(ataraxy/matches routes {:uri "/foo"})

=> [:foo]

```



If Ataraxy cannot correctly match any route, then an error result from

the `ataraxy.error` namespace is returned. For example:



```clojure

(ataraxy/matches routes {:uri "/bar"})

=> [:ataraxy.error/unmatched-path]

```



See the [errors](#errors) section for more details.



For performance, we can also pre-compile the routing data:



```clojure

(def compiled-routes (ataraxy/compile routes))

```



The resulting object can be used in `matches` in the same way as the

raw data structure:



```clojure

(ataraxy/matches compiled-routes {:uri "/foo"})

=> [:foo]

```



## Handlers



Once we have our routes, it's likely we want to turn them into a Ring

handler function. Ataraxy has a function called `handler` for this

purpose:



```clojure

(defn foo [request]

  {:status 200, :headers {}, :body "Foo"})



(def handler

  (ataraxy/handler

   {:routes   routes

    :handlers {:foo foo}}))

```



This function takes a map with four keys:



* `:routes`     - the routes to match

* `:handlers`   - a map of result keys to Ring handlers

* `:middleware` - a map of metadata keys to Ring middleware (optional)

* `:coercers`   - a map of symbols to coercer functions (optional)



The handler function is chosen by the key of the result. Two keys are

added to the request map passed to the handler:



* `:ataraxy/result` - contains the matched result

* `:route-params`   - a map of parameters matched in the path

                      (included for compatibility)



The handler can also return a result vector instead of a request

map. Each vector that is returned is checked against the handler map,

until eventually a Ring response map is returned.



The `ataraxy.response` namespace defines a number of responses on

the default handler, allowing for code like this:



```clojure

(require '[ataraxy.response :as response])



(defn hello [{[_ name] :ataraxy/result}]

  [::response/ok (str "Hello " name)])



(def handler

  (ataraxy/handler

    {:routes   '{[:get "/hello/" name] [:hello name]}

     :handlers {:hello hello}}))

```



The default handler is set to `ataraxy.handler/default`, but can be

changed by adding a handler to the `:default` key of the handler map.



Middleware is chosen based on the metadata that is applied to the

result or to the containing routing table. For example:



```clojure

(defn wrap-example [handler value]

  (fn [request]

    (let [response (handler request)]

      (assoc-in response [:header "X-Example"] value))))



(def handler

  (ataraxy/handler

   {:routes     {"/foo" ^:example [:foo]}

    :handlers   {:foo foo}

    :middleware {:example #(wrap-example % "test")}}))

```



This would add an `X-Example` header to the response of the

handler. We can also pass an argument to the handler by setting the

`:example` metadata key to something other than `true`:



```clojure

(def handler

  (ataraxy/handler

   {:routes     {"/foo" ^{:example "test"} [:foo]}

    :handlers   {:foo foo}

    :middleware {:example wrap-example}}))

```



Custom coercers can be added to the handler by specifying the

`:coercers` option. This is described in more detail in

the [coercers](#coercers) section.



## Syntax



Ataraxy generates routes from a **routing table**, which is a Clojure

map, or a list of alternating keys and values.



The keys of the table are **routes**, and the data type used defines a

way of matching and destructuring a request.



The values are either **results** or nested tables.



Here's a semi-formal definition of the syntax:



```

table  = {+} | (+)

route  = keyword | string | symbol | set | map | [route+]

result = table | [keyword symbol*]

```



### Results



Results are always vectors, beginning with a keyword, followed by zero

or more symbols. For example:



```clojure

[:foo id]

```



Results are paired with routes:



```clojure

{["/foo/" id] [:foo id]}

```



The symbols in the route are passed into the result.



The symbols in the result may be tagged with a type they should be

coerced into. For example:



```clojure

[:foo ^int id]

```



See the [coercers](#coercers) section for more detail.



### Keyword routes



A keyword will match the request method. For example:



```clojure

{:get [:foo]})

```



This route will match any request with the GET method.



### String routes



A string will match the `:path-info` or `:uri` key on the request. For

example:



```clojure

{"/foo" [:foo]

 "/bar" [:bar]}

```



This example will match the URIs "/foo" and "/bar".



### Symbol routes



Like strings, symbols match against the `:path-info` or `:uri` key on

the request. Unlike strings, they match on a regular expression, and

bind the string matched by the regular expression to the symbol.



By default the regex used is `[^/]+`. In other words, any character

except a forward slash. The regex can be changed by adding a `:re` key

to the symbol's metadata. For example:



```clojure

{^{:re #"/d.g"} w [:word w]}

```



This will match URIs like "/dog", "/dig" and "/dug", and add the

matched word to the result.



### Set routes



A set of symbols will match URL-encoded parameters of the same name.

For example:



```clojure

{#{q} [:query q]}

```



This will match any request with `q` as a parameter. For example,

"/search?q=foo".



In order to match query parameters, the request map needs a

`:query-params` key, which is supplied by the [wrap-params][]

middleware in Ring.



By default, the parameters must be set for the route to match. If you

want the parameters to be optional, you can prefix them with a "?".



```clojure

{#{?q} [:query ?q]}

```



This works the same as the previous example, except that the route

still matches if `q` is `nil`.



[wrap-params]: https://ring-clojure.github.io/ring/ring.middleware.params.html#var-wrap-params



### Map routes



A map will destructure the request. Any destructured symbol must not

be `nil` for the route to match. For example:



```clojure

{{{:keys [user]} :session} [:user user]}

```



This route will match any request map with a `:user` key in the

session.



As with set routes, symbols prefixed with a "?" are considered

optional and may be `nil`.



### Vector routes



A vector combines the behavior of multiple routing rules. For example:



```clojure

{[:get "/foo"] [:foo]}

```



This will match both the request method and the URI.



Strings and symbols will be combined in order, to allow complex paths

to be matched. For example:



```clojure

{[:get "/user/" name "/info"] [:get-user-info name]}

```



This will match URIs like "/user/alice/info" and pass the name "alice"

to the result.



### Nested tables



Nesting routing tables is an alternative way of combining routes.

Instead of a result vector, a map or list may be specified. For

example:



```clojure

{"/foo"

 {"/bar" [:foobar]

  "/baz" [:foobaz]}})

```



This will match the URIs "/foo/bar" and "/foo/baz".



You can also use nesting and vectors together:



```clojure

{["/user/" name]

 {:get [:get-user name]

  :put [:put-user name]}}

```



## Errors



When something goes wrong, Ataraxy returns one of the following error

results:



* `:ataraxy.error/unmatched-path`

* `:ataraxy.error/unmatched-method`

* `:ataraxy.error/missing-params`

* `:ataraxy.error/missing-destruct`

* `:ataraxy.error/failed-coercions`

* `:ataraxy.error/failed-spec`



If you're using the `ataraxy.core/handler` function, these are

automatically converted into appropriate Ring response maps. However,

it's generally worth customizing the error responses to the needs of

your application.



## Coercers



Coercers are functions that turn a string into a custom type. Any

symbol in the result can be tagged with a symbol associated with a

coercer function.



For example, it's common to want to change a parameter from a string

into an int:



```clojure

{[:get "/foo/" id] [:foo ^int id]}

```



The `int` and `uuid` coercers are included by default. We can easily

add our own, however:



```clojure

(defn ->float [s]

  (try (Double/parseDouble s) (catch NumberFormatException _)))



(def compiled-routes

  (ataraxy/compile

   '{[:get "/foo/" id] [:foo ^float id]}

   {'float ->float}))

```



And similarly to handlers:



```clojure

(def handler

  (ataraxy/handler

   {:routes   '{[:get "/foo/" id] [:foo ^float id]}

    :coercers {'float ->float}}))

```



## Specs



Results are validated via the `:ataraxy/result` spec. This is a

multi-spec that dispatches off the key, and can be assigned behavior

through the `result-spec` multimethod.



For example:



```clojure

(require '[clojure.spec.alpha :as s])



(defmethod ataraxy/result-spec ::foo [_]

  (s/cat :key any? :id nat-int?))

```



This ensures that any result with `::foo` as the key must have exactly

two elements, with the second being a natural number.



If a spec fails, then a `:ataraxy.error/failed-spec` result is

returned, which if left alone resolves to a 400 "Bad Request"

response in the handler.



## License



Copyright © 2022 James Reeves



Distributed under the Eclipse Public License either version 1.0 or (at

your option) any later version.