Snitch helps you create a production-grade HTTP layer for your applications and (micro)services with minimal effort. To create complete documentation for them with no effort.
Snitch is a thin layer built upon long-established and well-supported embedded web servers such as Undertow. Thanks to Kotlin's inlining capabilities the performance of Snitch is essentially the same as that of the underlying web server.
Our primary goals are:
- To create the most readable and maintainable API for creating web services
- By readable we mean readable production code where routes are complex, parameters need validation, parsing and mapping to domain types, errors need to be handled, deal with authentication and permissions, etc.
- To fully automate the creation of documentation for your services
- To have a strongly typesafe approach to HTTP layer modelling
- To be as lightweight and performant as possible
- To not use any reflection, annotations or code generation for production code
- To be async by default without sacrificing readability
- To be small and get out of the way. The HTTP layer is not the most interesting part of your application, and it should not be the most complex one either.
- To have a small learning curve despite it being a DSL
- Snitch
- How to install it
- Getting started
- Features
- Expressive routing
- Expressive handlers
- Expressive and exendable parameter definition, parsing and validation
- Strongly typed inputs and outputs
- Middleware
- Guards
- Fully automated documentation
- Performance
- Coroutines
- Small learning curve
- Learning resources
- Community support
- Why does it exist
- Who is it for?
- System requirements
- How to contribute
- Show Your Support
repositories {
maven(url="https://jitpack.io")
}
dependencies {
implementation("com.github.memoizr.snitch:bootstrap:3.3.1")
}snitch(GsonJsonParser)
.onRoutes {
GET("/hello") isHandledBy { "world".ok }
}
.start()
.serveDocumenation()val usersController = routes {
POST() with body<CreateUserRequest>() isHandledBy createUser
POST("login") with body<LoginRequest>() isHandledBy userLogin
userId / "posts" / {
authenticated {
GET() onlyIf principalEquals(userId) isHandledBy getPosts
POST() onlyIf principalEquals(userId) with body<CreatePostRequest>() isHandledBy createPost
GET(postId) isHandledBy getPost
PUT(postId) with body<UpdatePostRequest>() onlyIf principalEquals(userId) isHandledBy updatePost
DELETE(postId) onlyIf (principalEquals(userId) or hasAdminRole) isHandledBy deletePost
}
}
}...
val getPosts by handling {
postsRepository().getPosts(principal).toResponse.ok
}
val createPost by parsing<CreatePostRequest>() handling {
postsRepository().putPost(
CreatePostAction(
principal,
PostTitle(body.title),
PostContent(body.content),
)
)
.mapSuccess {
SuccessfulCreation(value).created
}.mapFailure {
FailedCreation().badRequest()
}
}
...val userId by path()
val postId by path(ofPostIdValidator)
val accessToken by header(ofValidAccessToken)
// Your custom parameter validation and parsing logic
val ofValidAccessToken = stringValidator("valid jwt") { jwt().validate(it) }Headers, paths, query parameters and bodies always require validation and mapping to domain types. Snitch makes it easy to do so.
val limit by query(ofNonNegativeInt(max = 30))
val offset by query(ofNonNegativeInt())
val postId by path(ofPostIdValidator)In the example above limit and offset are validated and mapped to UInt values. postId is validated and mapped to a PostId value object.
Therefore in the handler you can do this:
val getPosts by handling {
postsRepository().getPosts(request[userId], request[limit], request[offset]).toResponse.ok }The parameters are validated and safe to use. If they are not valid the request will not be handled and the client will receive a 400 Bad Request response with a list of reasons about all the parameters which are either not supplied or invalid.
Here's how you would define a simple logger middleware
val Router.log get() = using {
logger().info("Begin Request: ${request.method.name} ${request.path}")
next().also {
logger().info("End Request: ${request.method.name} ${request.path}")
}
}
val rootRouter = routes {
log {
"health" / healthController
"users" / usersController
}
}Endpoints can be configured with onlyIf and a condition or a condition expression to restrict access to the endpoint.
val usersController = routes {
...
userId / "posts" / {
authenticated {
...
DELETE(postId) onlyIf (principalEquals(userId) or hasAdminRole) isHandledBy deletePost
}
}
}Here authenticated is a guard that checks if the user is authenticated. principalEquals and hasAdminRole are defined as such in the user's codebase:
val hasAdminRole = condition {
when (role) {
ADMIN -> Successful()
else -> Failed(FORBIDDEN())
}
}
fun principalEquals(param: Parameter<out Any, *>) = condition {
if (principal.value == params(param.name)) Successful()
else Failed(FORBIDDEN())
}Snitch outputs OpenAPI 3.0 docs. Absolutely any of the inputs and any of the outputs are documented automatically, even response codes. No work or setup is required from the user to achieve this. Snitch allows the user to specify whether to serve the documentation on a given route. This is an interactive page based on Swagger-UI that allows a viewer to interact with the API, authenticate, and make any request and see the responses. You can optionally annotate individual fields of requests, responses or parameters to add additional descriptions or provide example values so that it'd be straightforward to use the API through the documentation page, as requests would be pre-populated with such example values. Documentation can either be served on the same service, or given to a doc aggregator that allows to provide a unified API for multiple services. Request, Response and parameter types are automatically generated exclusively from type information from the Kotlin language, hence they always represent the actual behaviour of the API.
Adding this line to the service configuration will generate the documentation and serve it on the /docs route, which can be configured along with the rest of the application settings.
.generateDocumentation()
.servePublicDocumenation()This is an example screenshot of the interactive Swagger-UI page that it serves at the /docs route:
Every endpoint can be interacted with, and the documentation is always up-to-date with the actual behaviour of the API.
Snitch uses Undertow as the default embedded web server. Undertow was chosen because it's the fastest embedded web server for the JVM for most use cases, and for its async-first approach based on NIO. It's also the most lightweight one, with a small classpath and a small memory footprint. That said, it's possible to use any other web server with Snitch, as it's not tied to Undertow in any way, so if another web server is preferred it can be used instead.
Snitch is designed to be only a very thin overlay on top of the embedded webserver, so it does not add any overhead to the request handling process. It's designed to be as fast as possible, and it's therefore almost as fast as the underlying web server is. Object instantiation is kept to a minium to not cause GC pressure. Call stack is also kept as shallow as possible. Reflection is not used at all, and the only reflection that happens is when the documentation is generated, which is an optional step for production code that would occour at most once during startup. This is done only once, and the results are cached, so it does not happen on every request. The application has a small classpath, and the only dependencies are the web server and the JSON library. This means that the application can be deployed as a single jar file, and it's easy to deploy and run it in a containerized environment. A small application complete with documentation can run in as little as 12MB of ram on top of the JVM. This library has been successfuly used in a variety of settings, from resource constrained environments such as Android to high performance environments such as high throughput microservices.
Snitch lets you use coroutine code seamlessly. For more information see the documentation.
The library is actually very small and a complete detailed overview can be had in a matter of hours. Powerful features such as guards, middleware and others are built on top of a small number of core concepts, and really there isn't any magic involved. The codebase only has a few thousand lines of code. Given a fluency of the Kotlin language it should be one of the easiest frameworks to truly understand how it works. Really it's just a thin wrapper around the embedded web server.
Please refer to the example folder for a reference implementation of a simple reddit-like service. The example tries to have production-like qualities such as handling authorization and authentication, database interaction, it shows how it works well and integrates with dependency injection libraries such as Shank. Also, please refer to the docs for a more detailed overview of the library as well as tutorials.
Join us on our discord server to ask questions, get help, or just to chat. We're a small but growing community but we're friendly and we're always happy to help.
Because code should be as readable as possible, and it should not require much ceremony to do simple stuff. If you want to do complex stuff it should be simple to extend the framework to do so. Resources are precious, you should not waste them on reflection or huge classpaths for doing basic stuff. Documentation is crucial, it should be generated automatically and be always up to date, and nobody should ever touch OpenAPI YAML or JSON files: we stand for these basic human rights.
- It's for those who like their code to look good, fast and be well documented.
- Those who don't like pomp and ceremony to do their basic boring tasks
- For those who'd take a smaller tool over a larger one to do the same job
- For those who like to control-click on a method to see what it's doing and not end up in a reflection hell
- For those who like to see their code compile and not have to wait for the runtime to tell them they made a typo
- Those who like aspects of Object-Oriented as well as Functional Programming and want to use both to their advantage
- Java 17 or higher
This library evolved over the years, initially as an internat tool deployed in a variety of scenarios, but now released as an open-source project. To contribute, please fork the repository and submit a pull request. We will review it as soon as possible. If you have any question open an issue, and we'll try to address it as soon as possible. Alternatively, join our discord server to get in touch. We have many beginner-friendly tasks, and we can offer plenty of support. This can be a great opportunity to learn some really advanced Kotlin concepts!
If you find this project useful, and you'd like to support our work, please consider giving it a ⭐️ on GitHub! Your support means a lot to us and helps us continue improving the library.
Click here to star the repo. Thank you!