play25-module-json-error-handler	play26-module-json-error-handler

Summary

A Play plugin that displays exceptions as JSON instead of HTML.

Add it to your build with Guice by adding the following config:

play.modules.enabled += "com.rallyhealth.playmodule.jsonerrors.guice.PlayJsonHttpErrorHandlerModule"
play.http.errorHandler = "com.rallyhealth.playmodule.jsonerrors.PlayJsonHttpErrorHandler"

Or for compile-time dependency injection, just override the httpErrorHandler component:

import com.rallyhealth.playmodule.jsonerrors.PlayJsonHttpErrorHandler
import play.api.{ApplicationLoader, BuiltInComponentsFromContext}
import play.api.http.HttpErrorConfig

class MyModuleFromContext(context: ApplicationLoader.Context) extends BuiltInComponentsFromContext(context) {

  lazy val httpErrorConfig: JsonHttpErrorConfig = JsonHttpErrorConfig.fromEnvironment(environment)

  override lazy val httpErrorHandler: HttpErrorHandler = new PlayJsonHttpErrorHandler(
    router,
    httpErrorConfig,
    sourceMapper
  )

  // ... other required components
}

Customization

You can create your own custom error handling with a mixin by extending JsonHttpErrorHandling[Json] or as a class by extending DefaultJsonHttpErrorHandler(...) with JsonHttpErrorHandling[Json]. The trait is parameterized on the type of json library you would like to use.

For a custom json library, all you need to do is implement:

import com.rallyhealth.playmodule.jsonerrors.JsonHttpErrorHandling
import play.api.UsefulException
import play.api.http.Writeable
import play.api.mvc.RequestHeader

trait MyJsonHttpErrorHandling extends JsonHttpErrorHandling[MyJson] {
  override implicit protected def writeable: Writeable[MyJson] = {
    // TODO: Provide a converter for MyJson into a ByteString with the appropriate content-type 
    ???  
  }
  override protected def jsonify(
    request: RequestHeader,
    responseStatus: Int,
    error: Either[String, UsefulException]): MyJson = {
    // TODO: Serialize these values into a json response
    ???    
  }
}

If you want to use Play's json library, you can just extend PlayJsonHttpErrorHandling or the PlayJsonHttpErrorHandler class (depending on whether you want to mixin other behavior). You can override the way exceptions are serialized, as well as transform or replace the shape of the json with:

import com.rallyhealth.playmodule.jsonerrors.PlayJsonHttpErrorHandling
import play.api.UsefulException
import play.api.http.Writeable
import play.api.mvc.RequestHeader

trait MyJsonHttpErrorHandling extends PlayJsonHttpErrorHandling {
  override protected def exceptionJsonWriter: OWrites[Throwable] = {
    // TODO: Provide Writes for exception to Json (potentially recursively on causes / suppressed exceptions)
    ???
  } 
  override protected def jsonify(
    request: RequestHeader,
    responseStatus: Int,
    error: Either[String, UsefulException]): JsValue = {
    // TODO: Transform the json result
    super.jsonify(request, responseStatus, error)
  }
}