Improve client-side error response messages

- add custom exception handler + exception case classes
- propagate error messages back to the client with 400s if they're known
  errors & 500 if they're unknown

api/src/main/scala/ErrorHandler.scala

@@ -0,0 +1,42 @@
+package org.wikiwatershed.mmw.geoprocessing
+
+import akka.http.scaladsl.model._
+import akka.http.scaladsl.server._
+import StatusCodes.{BadRequest,InternalServerError}
+import Directives._
+
+sealed trait GeoprocessingException extends Exception
+case class MissingTargetRasterException() extends GeoprocessingException()
+case class MissingVectorCRSException() extends GeoprocessingException()
+case class MissingVectorException() extends GeoprocessingException()
+case class InvalidOperationException(val message: String) extends GeoprocessingException()
+case class UnknownCRSException(val crs: String) extends GeoprocessingException()
+
+trait ErrorHandler {
+  val geoprocessingExceptionHandler = ExceptionHandler {
+    case InvalidOperationException(ex) => {
+      println(s"Invalid operation type: $ex")
+      complete(HttpResponse(BadRequest, entity = ex))
+    }
+    case MissingTargetRasterException() => {
+      println("Input error: Missing required targetRaster")
+      complete(HttpResponse(BadRequest, entity = "Missing required targetRaster"))
+    }
+    case ex: MissingVectorCRSException => {
+      println("Input error: Missing required vectorCRS")
+      complete(HttpResponse(BadRequest, entity = "Missing required vectorCRS"))
+    }
+    case ex: MissingVectorException => {
+      println(s"Input error: Missing required vector")
+      complete(HttpResponse(BadRequest, entity = "Missing required vector"))
+    }
+    case UnknownCRSException(crs) => {
+      println(s"Unknown CRS error: $crs")
+      complete(HttpResponse(BadRequest, entity = "Unknown CRS"))
+    }
+    case e: Exception => {
+      println(s"Exception: $e")
+      complete(HttpResponse(InternalServerError, entity = s"$e"))
+    }
+  }
+}

api/src/main/scala/Geoprocessing.scala

@@ -36,14 +36,14 @@ trait Geoprocessing extends Utils {
     * @param   input  The InputData
     * @return         A histogram of results
     */
+  @throws(classOf[MissingTargetRasterException])
   def getRasterGroupedAverage(input: InputData): Future[ResultDouble] = {
     val aoi = createAOIFromInput(input)
     val futureLayers = cropRastersToAOI(input.rasters, input.zoom, aoi)
     val targetLayer = input.targetRaster match {
       case Some(targetRaster) =>
         cropSingleRasterToAOI(targetRaster, input.zoom, aoi)
-      case None =>
-        throw new Exception("Request data missing required 'targetRaster'.")
+      case None => throw new MissingTargetRasterException
     }
     val opts = getRasterizerOptions(input.pixelIsArea)
 
@@ -62,6 +62,8 @@ trait Geoprocessing extends Utils {
     * @param   input  The InputData
     * @return         A histogram of results
     */
+  @throws(classOf[MissingVectorException])
+  @throws(classOf[MissingVectorCRSException])
   def getRasterLinesJoin(input: InputData): Future[ResultInt] = {
     val aoi = createAOIFromInput(input)
     val futureLayers = cropRastersToAOI(input.rasters, input.zoom, aoi)
@@ -70,11 +72,9 @@ trait Geoprocessing extends Utils {
         input.vectorCRS match {
           case Some(crs) =>
             createMultiLineFromInput(vector, crs, input.rasterCRS)
-          case None =>
-            throw new Exception("Request data missing required 'vectorCRS'.")
+          case None => throw new MissingVectorCRSException
         }
-      case None =>
-        throw new Exception("Request data missing required 'vector'.")
+      case None => throw new MissingVectorException
     }
 
     futureLayers.map { rasterLayers =>

api/src/main/scala/Utils.scala

@@ -153,11 +153,12 @@ trait Utils {
     * @param   crs  The key (e.g. "input.rasterCRS")
     * @return       A CRS
     */
+  @throws(classOf[UnknownCRSException])
   def getCRS(crs: String): CRS = crs match {
     case "LatLng" => LatLng
     case "WebMercator" => WebMercator
     case "ConusAlbers" => ConusAlbers
-    case s: String => throw new Exception(s"Unknown CRS: $s")
+    case s: String => throw new UnknownCRSException(s)
   }
 
   /**

api/src/main/scala/WebServer.scala

@@ -32,27 +32,32 @@ object PostRequestProtocol extends DefaultJsonProtocol {
   implicit val resultDoubleFormat = jsonFormat1(ResultDouble)
 }
 
-object WebServer extends HttpApp with App with LazyLogging with Geoprocessing {
+object WebServer extends HttpApp with App with LazyLogging with Geoprocessing with ErrorHandler {
   import PostRequestProtocol._
 
+  @throws(classOf[InvalidOperationException])
   def routes: Route =
-    get {
-      path("ping") {
-        complete("pong")
-      }
-    } ~
-    post {
-      path("run") {
-        entity(as[PostRequest]) { data =>
-          data.input.operationType match {
-            case "RasterGroupedCount" =>
-              complete(getRasterGroupedCount(data.input))
-            case "RasterGroupedAverage" =>
-              complete(getRasterGroupedAverage(data.input))
-            case "RasterLinesJoin" =>
-              complete(getRasterLinesJoin(data.input))
-            case _ =>
-              throw new Exception(s"Unknown operationType: ${data.input.operationType}")
+    handleExceptions(geoprocessingExceptionHandler) {
+      get {
+        path("ping") {
+          complete("pong")
+        }
+      } ~
+      post {
+        path("run") {
+          entity(as[PostRequest]) { data =>
+            data.input.operationType match {
+              case "RasterGroupedCount" =>
+                complete(getRasterGroupedCount(data.input))
+              case "RasterGroupedAverage" =>
+                complete(getRasterGroupedAverage(data.input))
+              case "RasterLinesJoin" =>
+                complete(getRasterLinesJoin(data.input))
+              case _ => {
+                val message = s"Unknown operationType: ${data.input.operationType}"
+                throw new InvalidOperationException(message)
+              }
+            }
           }
         }
       }