API-First bootstrapping tool for building RESTful web services from a Swagger/OpenAPI spec
MIT License
API-First-Hand is an API-First bootstrapping tool for building RESTful web services from a Swagger/OpenAPI specification. Constructed as a plugin, it takes your Swagger/OpenAPI definition as the single source of truth and regenerates these code snippets for you, simply and consistently. Instead of writing lots of boilerplate code, you can focus instead on implementing service business logic. Subsequent regenerations keep the code that you have added—either by commenting out the parts that are no longer valid, or by adding parts that are needed because you've changed the API.
We built API-First-Hand for use with Play Framework, but we would like to extend it for use with Akka HTTP. Get in touch if you'd like to help make that possible.
Api-First-Hand supports round-trip regeneration and compilation of:
Managed means "managed by sbt"—and this means that you don't have to control or change the code as you make your REST service. The security extractors and unmarshallers are available through manual generation and compilation, and supported if A) No security extractor or unmarshaller with the same name already exists; B) The developer issues the playScalaSecurity
or playScalaMarshallers
sbt command.
API-First-Hand is under active development and should not be considered production-ready.
To use the plugin, you need:
The Activator template provides a sandbox for your application to run with API-First-Hand. (Download Activator here, then follow the instructions). It contains the following:
public/swagger
folder)plugins.sbt
file with a definition of all required resolvers and plugins (found in the project
folder)conf
folder with the following customized contents:
routes
file with route configuration for Swagger UI, example specification, and commented-out links to other examplesexample.yaml
, with a dummy implementation in the app
folderexamples
folder containing additional Swagger specification examples, each representing some aspect of Api-First-Hand in greater detail. For the plugin to pick up the specification, move it into the conf
folder. You can simultaneously have multiple Swagger specifications in the conf
folder.app
directory with following template implementations:
controllers/Swagger.scala
: a backend side of the Swagger UIgenerated_controllers/example.yaml.scala
: a dummy implementation of the example controller that's (re)generated if deletedsecurity/example.yaml.scala
: a marshaller for OAuth2 tokens. Will not be regenerated until either deleted or renamed; and then explicitly requested by issuing a playScalaSecurity
command.activator new hello-world api-first-hand
project/plugins.sbt
of your generated project and add the required plugins and resolvers therebuild.sbt
.yaml
or .json
extension into the conf
directory->
) to the Play's routes fileNow let's run your application with the plugin:
cd
into your service project directory.sbt
and run
the service.A single specification defines a single API; in our case, these are three API endpoints:
GET /token
API plays a role of an authentication server and is used by the Swagger UI for OAuth token requests.POST /token
API represents an authorization server and is used by the security part of the generated code to validate OAuth tokens.GET /todos/{user_id}
takes a path parameter user_id
and returns a TODO list for the given user. Use security/example.yaml.scala
, the marshaller for OAuth2 tokens, to request an OAuth token with the scope admin:org
. This will grant permission for the client to access this endpoint and enable you to test the API.Click the default button to expand the API definition in the Swagger UI. You can change the specification or write some backend code and use the Swagger UI to see the results.
Play application developers are used to defining endpoints in the conf/routes
file. With Api-First-Hand, however, Swagger API specifications already define endpoints as path
definitions—saving you from doing the work twice. Just link your API definition in the routes file once. This makes all Swagger API-defined endpoints available as children of a single path context location, and generates Play route definitions from them (as shown below):
-> /example example.yaml.Routes
The conf/routes
file provided by the Activator template also contains additional GET
mappings required for the Swagger UI sandbox, and some commented-out links to other examples. If you activate some specification by moving it from the examples
folder into the conf
folder, you'll have to uncomment an appropriate line in the routes
file so that Play can find routes generated for it.
API-First-Hand generates Scala domain model definitions for all data types defined as Swagger parameters in an API specification. Swagger parameters can be of path, query, header, form or body types, and consist of either primitive data types or more complex types composed from objects and arrays with primitives as leaves. Both primitive types and complex types are mapped to Scala.
For more information and an example, go here.
Swagger version 2.0 allows for primitive data types based on the types defined by JSON-Schema. When generated as Scala, the mapping indicated in this chart applies.
Complex types are made up of either primitive objects or nested objects. Go here for details and examples related to Objects (nested objections, optionality, object extensions, polymorphism, and additional properties) and Arrays (including nested arrays).
You can use a filename to reference part of another specification with the $ref
element. You can split a single specification into multiple files (as shown in cross_spec_references.yaml
), and also reference a definition in one specification across other specifications. (For example, you can create domain_model.yaml
and then reference it from any other API specification.)
An independent copy of the class definition is created for each referencing specification. The definition is then placed into the appropriate package for each specification.
Therefore, even if multiple classes with the same name and structure are generated, they all will coexist in their own separate namespaces and won't be interchangeable. (We plan to change this in future versions.)
Swagger API definitions allow you to impose constraints on parameter types. You can use the required
constraint to mark a parameter or specific field within a domain definition, as required upon input. You can also add to your API definition more constraints, as defined by the Parameter Object. API-First-Hand will generate validations for these parameter constraints and make sure that your controller methods are only called if the input of your service complies to those constraints.
Go here for more information and examples.
Go here for more detailed information about test generators.
to build a plugin from sources, do the following:
sbt publishLocal
in the API-First-Hand directoryApi-First-Hand has a three-tier architecture, with pluggable specification parsers and pluggable artefact generators:
By separating the specification and generation tiers, we can plug in different specification standards and generate source code for different frameworks.
There are a couple of sub-projects:
swagger-model
: A standalone Scala Swagger model with Jackson parser. Can be used by another projects.api
: Automatically added to the runtime classpath of any projects using API-First-Hand.swagger-parser
: A converter of the Swagger model to the internal AST of the pluginapi-first-core
: This is a core of the plugin with minimal functionality. It includes defining an AST structure and some transformations on AST.play-scala-generator
: The standalone generator for transforming an AST into the skeleton of Play-Scala application.plugin
: sbt plugins, one for each tier:
ApiFirstSwaggerParser
: wraps the Swagger-parsing partApiFirstCore
: wrapper for AST-related functionalityApiFirstPlayScalaCodeGenerator
: a wrapper for the Play-Scala generatorYou must enable each module separately in sbt's build.sbt
and configure which parser(s) the plugin will use, like this:
lazy val root = (project in file(".")).enablePlugins(PlayScala, ApiFirstCore, ApiFirstPlayScalaCodeGenerator, ApiFirstSwaggerParser)
apiFirstParsers := Seq(ApiFirstSwaggerParser.swaggerSpec2Ast.value).flatten
Check out the Activator template's configuration for a complete example.
The PlayScala generator supports custom templates. In order to override default template for some of the components, please provide your custom template named in accordance to the following list:
play_scala_test.mustache
: for unit testsplay_validation.mustache
: for validatorsgenerators.mustache
: for test data generatorsmodel.mustache
: for model classes and query and path bindablesplay_scala_controller_base.mustache
: for Play controller basesplay_scala_controller_security.mustache
: for security adapters used by controller basesplay_scala_form_parser.mustache
: for form parsers used by the controller basesplay_scala_controller.mustache
: for Play controller skeletons; you can augment themplay_scala_response_writers.mustache
: for custom serializers; you can augment themplay_scala_security_extractors.mustache
: for custom security extractors; you can augment themGenerated artifacts must preserve some specific shape to be compiled together without errors.
You must configure the location for custom templates by overriding the plugin setting playScalaCustomTemplateLocation
. For example, this configuration will set the project's conf/templates
folder as the location:
playScalaCustomTemplateLocation := Some(((resourceDirectory in Compile) / "templates").value)
sbt doesn't allow sub-projects to depend on each other as sbt plugins. To test an sbt plugin, you need a separate
project. This project is swagger-tester
. To test your changes as you're developing the plugin, cd into this
directory, and run sbt. This project uses an sbt ProjectRef
to the sbt plugin, which means you don't need to
publishLocal
the plugin after each change. Just run reload
in the sbt console, and it will pick up your changes.
API-First-Hand provides a few commands useful for development:
apiFirstPrintDenotations
: outputs common names of different parts of the AST as they are intended for use in generated Scala codeapiFirstPrintRawAstTypes
: outputs all type definitions as they read from the specification before type optimizationsapiFirstPrintRawAstParameters
: outputs all parameters definitions before type optimizationsapiFirstPrintFlatAstTypes
: outputs type definitions after type optimizationsapiFirstPrintFlatAstParameters
: outputs parameter definitions after type optimizationsWe're using the sbt scripted framework for testing. You can find the tests in plugin/src/sbt-test
and run them
by running scripted
in the sbt console.
Some quality checks are embedded into the build script:
scalastyle
sbt command: use this to perform code style checks before putting changes into the repositorylint:compile
sbt command: use this to perform static code analysis before putting changes into the repositorysbt clean coverage test
command. Generate coverage statistics with the coverageReport
sbt command.command shall be used to ... before putting changes into the repository