An HTTP Framework built with Kotlin for the JVM.
Wasabi combines the conciseness and expressiveness of Kotlin, the power of Netty and the simplicity of Express.js (and other Sinatra-inspired web frameworks) to provide an easy to use HTTP framework
An HTTP framework that allows you to easily create back-end services for a web application or any other type of application that might require an HTTP API.
It is not an MVC framework. There is no View Engine or templating language. You can combine it with client-side frameworks such as AngularJS or Ember. If you want a fully-fledged MVC framework in Kotlin, take a look at Kara
It is not a REST framework. Primarily because there's no such thing, and while calling it REST might sell better, it would be false. However it does provide (and will provide) features that allow you to create resource-orientated systems that help comply with ReSTful constraints.
In development. A lot of the stuff here is not ready for production. There are many experiments, quite a few hacks and things that are just wrong. So be warned.
A lot of the API and design of this framework is based on experience developing applications with other HTTP frameworks and the needs that have arised. However, like any framework, until you don't have several usages of it, it's hard to know if you got it right. So while I'm hoping that there won't be major API changes, some things might change over time.
var server = AppServer()
server.get("/", { response.send("Hello World!") })
server.start()The easiest way to use Wasabi is with Gradle.
-
Download Gradle.
-
Create the build.gradle file and import it into your IDE.
To create this file you can either:
-
Have Gradle generate the file for you (easiest) running the build.gradle file under tools (Recommended). To use this option download the file in tools/build.gradle and type
gradlefor more info
-
Create it manually. See the sample for the structure. Make sure you fill in the TODOs
For Gradle projects, 0.1-SNAPSHOT version can be included like this (build.gradle file):
repositories {
// Other repositories you use.
maven { url 'http://repository.jetbrains.com/all' }
}
dependencies {
// Other dependencies you use.
compile 'org.wasabi:wasabi:0.1-SNAPSHOT'
}
All versions can be found here: http://repository.jetbrains.com/all/org/wasabi/wasabi/
Kotlin is still in development and so is Wasabi. The current master trunk of Wasabi (under 0.1-SNAPSHOT) uses the latest nightly build of Kotlin. As such, if you're using a released version of Kotlin, such as M8, you'll get binary format errors. To use the latest nightly builds of Kotlin (recommendeded), add the following repository to IntelliJ IDEA:
http://teamcity.jetbrains.com/guestAuth/repository/download/bt345/.lastSuccessful/updatePlugins.xml
under Preferences | Plugins | Browse Repositories | Manage Repositories
and you'll be able to install the latest plugin. Alternatively if you're not using IntelliJ IDEA, you can download the artifacts from:
http://teamcity.jetbrains.com/project.html?projectId=Kotlin&tab=projectOverview
Each Wasabi application is composed of a single AppServer on which you define route handlers. A route handler can respond to any of the HTTP verbs: GET, POST, PUT, DELETE, OPTIONS, HEAD. A normal application consists of a section where you define a series of parameters for the application, followed by your handlers (i.e. your routing table).
var appServer = AppServer()
server.get("/customers", { .... } )
server.post("/customer", { .... } )
server.start()In Wasabi, every request is processed by one or more route handlers. In the previous example, we are responding to a GET to "/" with the text "Hello World!". You can chain route handlers. For instance, if you want to log information about a request (this is actually built-in so no need to do it manually), you could do
server.get("/",
{
val log = Log()
log.info("URI requested is ${request.uri}")
next()
},
{
response.send("Hello World!")
}
)or as follows enforces JSON serialisation regardless of the request accept header.
server.get("/",
{
val log = Log()
log.info("URI requested is ${request.uri}")
next()
},
{
response.send("Hello World!", "application/json")
}
)By calling next() on each handler, the processing will continue.
All verbs on AppServer have the following signature
fun get(path: String, vararg handlers: RouteHandler.() -> Unit) {
addRoute(HttpMethod.GET, path, *handlers)
}where you can pass one or multiple route handlers. Each one of these is an extension method to the class RouteHandler. This class has various properties, amongst which are request and response. That is how you can access these properties from inside each of the functions without an explicit declaration.
Wasabi supports route parameters. Define as many parameters as you like using : followed by the name of the parameter. Access it via request.routeParams["name"]
server.get("/customer/:id", { val customerId = request.routeParams["id"] } )Access query parameters using queryParams property of the request.
http://localhost:3000/customer?name=Joe
server.get("/customer", { val customerName = request.queryParams["name"] } )Access form parameters using bodyParams property of the request.
server.post("/customer", { val customerNameFromForm = request.bodyParams["name"] } )How you layout the code for your application or group your routes depends largely on your own choice. One thing I've always been against is forcing people to group routes per class for instance. Having said that, there are some bounds you need to stay in.
Defining logic for each route handler inline:
val appServer = AppServer()
appServer.get("/customer", { response.send(customers) })For very simple operations this might be ok however, it will soon become unmaintainable.
Define route handlers as functions and reference them:
val appServer = AppServer()
appServer.get("/customer", getCustomers)
This means that your definition of route handlers pretty much becomes a routing table, which is what it should be.
This is the preferred option. You can then group functions however way you want:
Group similar routes in its own file. As Kotlin allows top level functions, you do not need to have a class to group functions. As such, you could have a file name CustomerRouteHandlers.kt for instance with:
val getCustomers = routeHandler {
response.send(customers)
}
val getCustomerById = routeHandler {
...
} routeHandler is a syntatic sugar to define the type of the route handler. You could also have writte that as:
val getCustomers : RouteHandler.() -> Unit = {
response.send(customers)
}
val getCustomerById : RouteHandler.() -> Unit = {
...
} If for some reason you want to group by class, you can do so. Best way is to use a companion object
class CustomerRoutes {
companion object {
val createCustomer = routeHandler {
}
}
}Note Kotlin allows you to refer to a function by name using :: syntax. In principle you could also do:
appServer.get("/customer", ::getCustomer)and not require an explicit variable declaration for the function. However, this currently does not work with extension functions but hopefully will in the future.
In addition to handlers, Wasabi also has interceptors. These allow you to intercept a request and decide whether you want it to continue or not (returning false would stop processing). Since you have access to both the request and response, you can do whatever you need. Think of interceptors as a way to add functionality to every request, or a those matching a certain route pattern. Some frameworks have popularized the term middleware to refer to something that intercepts a request/response. I do not agree with such a broad and somewhat ambiguous term. I like to name things as close to what they actually do. An interceptor implements the following interface
interface Interceptor {
fun intercept(request: Request, response: Response): Boolean
}You return true if you want the process to continue or false if you want to interrupt the request.
To add an interceptor to the application, you use
server.interceptor(MyInterceptor(), path, position)where path can be a specific route or *** to match all routes. Position indicates when the intercept occurs. Possible positions are
enum class InterceptOn {
PreRequest
PreExecution
PostExecution
PostRequest
Error
}Out of the box, the following interceptors are available
- BasicAuthenticationInterceptor: Basic authentication
- ContentNegotiationInterceptor: Automatic Content negotation
- FavIconInterceptor: Support for favicon
- StaticFileInterceptor: Support for serving static files
- LoggingInterceptor: Logging
- FileBasedErrorInterceptor: Customize error messages based on convention (e.g. 404.html)
- SessionManagementInterceptor: Session Management support
Most interceptor add extension methods to AppServer to make them easier (and more descriptive) to use. For instance the ContentNegotiationInterceptor and StaticFileInterceptor would be used as so
val appServer = AppServer()
server.negotiateContent()
server.serveStaticFilesFromFolder("/public") Wasabi ships with content negotiation out of the box, via a couple of interceptors. In particular:
-
ContentNegotiationParserInterceptor (still looking for a better name) Allows you to indicate to Wasabi to not only take into account Accept Headers but also Query Fields and Extensions on documents
-
ContentNegotiationInterceptor Does the actual content negotiation, finding the appropriate serializer.
Sometimes you want to not only do Content Negotiation using the Accept headers, but also using a query field (for instance format=json) or extensions to documents (e.g. /customer.json).
The ContentNegotiationParser allows you to do this. Easiest way to use it is via the extension function:
server.parseContentNegotiationHeaders() {
onQueryParameter("format")
onExtension()
onAcceptHeader()
}Based on the order in which you pass in onAcceptHeader, onExtension and onQueryParameter defines the priority. Above for instance first the Query Parameter is taking into account, then extension and lastly the Accept Header
QueryParameter defaults to the query parameter format but you can pass in a different one. Both onExtension and onQueryParameter also take a list of mappings, which an array of extension to media type. By default json maps to application/json and xml to application/xml
By default Content Negotiation is enabled. You can disable it via the AppConfiguration. You can then just send and object you want and Wasabi will automatically serialize it and send it back to the client.
server.get("/customer/:id", {
val customer = getCustomerById(request.params["id"])
response.send(customer)
}Wasabi will automatically serialize that into Json, Xml or any other media type supported (see Serializers below)
If you need to manually override Content Negotiation, you can do so using the negotiate function on response
server.get("/customer/:id", {
val customer = getCustomerById(request.params["id"])
response.negotiate (
"text/html" with { send("Joe Smith") },
"application/json" with { send(customer) }
}
}negotiate signature is:
fun negotiate(vararg negotiations: Pair<String, Response.() -> Unit>)You can pass in an unlimited number of media type, functions. Also, as the function is an extension function to Response, you have access to the response functions directly. That is why we can just write send as opposed to response.send.
Note that even if you use manual content negotiation, Wasabi will still try and serialize the object for you based on the media type.
Both manual as well as automatic Content Negotiation use serializers. Wasabi ships with Json and XML (TODO) serializers. These are defined as a property of the AppServer.
Each Serializer can take as parameters a variable number of strings which define regular expressions for the media types it can handle. JsonSerializer for instance takes:
class JsonSerializer(): Serializer("application/json", "application/vnd\\.\\w*\\+json")Wasabi provides CORS support via an Interceptor. You can enable CORS support in multiple ways:
- Via AppConfiguration.enableCORSGlobally - which enables CORS for all routes, all verbs, all origins
- Programatically using server.enableCORSGlobally - same as above
- Programatically using server.enablesCORS([...COREntry...]) - providing an array of CORSEntry's
Each CORSEntry consists of:
class CORSEntry(val path: String = "*",
val origins: String = "*",
val methods: String = "GET, POST, PUT, DELETE",
val headers: String = "Origin, X-Requested-With, Content-Type, Accept",
val credentials: String = "",
val preflightMaxAge: String = "") {
}with the corresponding defaults. Obviously you should only have one default.
Wasabi can automatically respond to OPTIONS for a specific path. You can enable this in multiple ways:
- Via AppConfiguration.enableAutoOptions
- Programatically using server.enableAutoOptions - same as above
Wasabi allows registration of custom handlers by exception type also. You can register them as follows:
val appServer = AppServer()
appServer.exception(MyKewlException::class, {
reponse.setStatus(418, "My brew is not as strong as yours!")
response.send("Out of beans: ${exception.message}")
})like other Wasabi handlers the registered exception handler gets passed the request and response as well as the exception thrown.
We're mostly hanging out on the #wasabi Channel on Kotlin's Slack. Join us there for questions and discussions.
There's a lot of work still pending and any help would be appreciated. Pull Requests welcome!
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Licensed under Apache 2 OSS License