A simple wrapper for using Sangria from within Finch.
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Finch GraphQL support

Some simple wrappers around Sangria to support its use in Finch.

It is a small layer, that is reasonably opininated, which may not be to your liking. In particular:

  • We transport GraphQL queries as JSON, over HTTP. This necessitates some nasties from time to time.
  • We use Twitter classes instead of the standard library, for things like Future and Try.
  • We use Futures containing Options or Eithers instead a failing Future. Failing Futures are only used for things that we'd not reasonably expect a client to be able to handle (i.e. something catastrophic).
  • We handle variables in the form of a JSON encoded string (for example from GraphiQL), as well as a straight JSON object.
  • We do our best to give back semi-sane HTTP status codes.
  • We expect that you want strong types for things.

There are some things that need improvement, including:

  • We are hard coded to Circe, it should be fairly easy to decouple it should you so wish.
  • In the same vein, the executor returns Json, mainly because of the CirceResultMarshaller. Ideally both of these would use some form of class that represented the variables/results, and defined an InputUnmarshaller and a ResultMarshaller for them respectively. In particular, this leads to the unpleasantness with the re-parsing of the JSON returned from the underlying executor to find the status of the result.

If you like this, you might like other open source code from Redbubble:

  • rb-scala-utils - Miscellaneous utilities (common code) for building Scala-based services, using Finch (on which this project depends).
  • finch-template - A template project for Finch-based services.
  • rb-graphql-template - A template for Scala HTTP GraphQL services.
  • finagle-hawk - HTTP Holder-Of-Key Authentication Scheme for Finagle.


You will need to add something like the following to your build.sbt:

resolvers += Resolver.jcenterRepo

libraryDependencies += "com.redbubble" %% "finch-sangria" % "0.3.8"


  1. Configure the executor:

    val schema = ...           // your Sangria schema
    val context = ...          // your root context
    val errorReporter = ...    // a way to log errors, e.g. Rollbar
    val serverMetrics = ...    // your stats receiver
    val logger = ...           // a logger
    val executor = GraphQlQueryExecutor.executor(
      schema, context, maxQueryDepth = 10)(errorReporter, serverMetrics, logger)

Set the max depth to whatever suits your schema (you'll likely need >= 10 for the introspection query).

  1. Write your endpoint:

    import com.redbubble.graphql.GraphQlRequestDecoders.graphQlQueryDecode
    object GraphQlApi {
      val stats = StatsReceiver.stats
      def graphQlGet: Endpoint[Json] =
        get("graphql" :: graphqlQuery) { query: GraphQlQuery =>
      def graphQlPost: Endpoint[Json] =
        post("graphql" :: jsonBody[GraphQlQuery]) { query: GraphQlQuery =>
      private def executeQuery(query: GraphQlQuery): Future[Output[Json]] = {
        val operationName = query.operationName.getOrElse("unnamed_operation")
        stats.counter("count", operationName).incr()
        Stat.timeFuture(stats.stat("execution_time", operationName)) {
      private def runQuery(query: GraphQlQuery): Future[Output[Json]] = {
        val result = executor.execute(query)(globalAsyncExecutionContext)
        // Do our best to map the type of error back to a HTTP status code
        result.map {
          case SuccessfulGraphQlResult(json) => Output.payload(json, Status.Ok)
          case ClientErrorGraphQlResult(json, _) => Output.payload(json, Status.BadRequest)
          case BackendErrorGraphQlResult(json, _) => Output.payload(json, Status.InternalServerError)
  2. Bring the response encoder into scope when you create your Service:

    import com.redbubble.graphql.GraphQlEncoders.graphQlResultEncode
    val api = GraphQlApi.graphQlGet :+: GraphQlApi.graphQlPost
    val service = api.toServiceAs[Application.Json]
    Http.server.serve(":8080", service)


If you want to integrate GraphiQL (you should), it's pretty easy.

  1. Pull down the latest GraphiQL file.

  2. You may need to adjust the paths within the GraphiQL file if you're using versioned paths, etc.

  3. Stick it somewhere in your classpath.

  4. Write an endpoint for it:

    object ExploreApi {
      private val graphiQlPath = "/graphiql.html"
      def explore: Endpoint[Response] = get("explore") {
        classpathResource(graphiQlPath).map(fromStream) match {
          case Some(content) => asyncHtmlResponse(Status.Ok, AsyncStream.fromReader(content, chunkSize = 512.kilobytes.inBytes.toInt))
          case None => textResponse(Status.InternalServerError, Buf.Utf8(s"Unable to find GraphiQL at '$graphiQlPath'"))
        private def classpathResource(name: String): Option[InputStream] = Option(getClass.getResourceAsStream(name))

Other Fun Bits

We've added some other bits & pieces to make using Sangria easier.

Scalar types

There are various helpers that can help you define Scalar types. For example to add support for a tagged type:

// Set up a tagged type

import shapeless.tag
import shapeless.tag._

trait PixelWidthTag
type PixelWidth = Int @@ PixelWidthTag
def PixelWidth(w: Int): @@[Int, PixelWidthTag] = tag[PixelWidthTag](w)

// Define your GraphQL type for the tagged type

private val widthRange = 1 to MaxImageDimension
private implicit val widthInput = new ScalarToInput[PixelWidth]

private case object WidthCoercionViolation
    extends ValueCoercionViolation(s"Width in pixels, between ${widthRange.start} and ${widthRange.end}")

private def parseWidth(i: Int) = intValueFromInt(i, widthRange, PixelWidth, () => WidthCoercionViolation)

val WidthType = intScalarType(
  s"The width of an image, in pixels, between ${widthRange.start} and ${widthRange.end} (default $DefaultImageWidth).",
  parseWidth, () => WidthCoercionViolation)

val WidthArg: Argument[PixelWidth] = Argument(
  name = "width",
  argumentType = OptionInputType(WidthType),
  description = s"The width of an image, in pixels, between ${widthRange.start} and ${widthRange.end} (default $DefaultImageWidth).", defaultValue = DefaultImageWidth)

Input types

We've also added support for input types, in a similar way to how other types are handled, they are typesafe.

// Tagged type
trait PushNotificationTokenTag
type PushNotificationToken = String @@ PushNotificationTokenTag
def PushNotificationToken(t: String): @@[String, PushNotificationTokenTag] = tag[PushNotificationTokenTag](t)

// GraphQL type
private case object PushNotificationTokenCoercionViolation
    extends ValueCoercionViolation(s"Push notification token expected")

private def parseToken(s: String): Either[PushNotificationTokenCoercionViolation.type, PushNotificationToken] =

val PushNotificationTokenType =
    "PushNotificationToken", s"An iOS push notification token.",
    parseToken, () => PushNotificationTokenCoercionViolation

val PushNotificationTokenArg =
  Argument("token", PushNotificationTokenType, description = s"An iOS push notification token.")

// Input type for our type
val FieldPushNotificationToken = InputField(
  "If available, the push notification token for the device. May be empty if the user has not given permission to send notifications."

val RegisterDeviceType: InputObjectType[DefaultInput] =
    name = "RegisterDevice",
    description = "Register device fields.",
    fields = List(FieldPushNotificationToken, FieldBundleId, FieldAppVersion, FieldOsVersion)

val RegisterDeviceArg = Argument(InputFieldName, RegisterDeviceType, "Register device fields.")

// Let's use that type in a mutation

object DeviceRegistration extends InputHelper {
  def registerDevice(ctx: Context[RootContext, Unit]): Action[RootContext, RegisteredDevice] = {
    val token = ctx.inputArg(FieldPushNotificationToken).flatten
    val registeredDevice = for {
      bundleId <- ctx.inputArg(FieldBundleId)
      appVersion <- ctx.inputArg(FieldAppVersion).flatMap(fromRawVersion)
      osVersion <- ctx.inputArg(FieldOsVersion).flatMap(fromRawVersion)
    } yield {
      val device = Device.device(token, App(bundleId, appVersion), osVersion)
    registeredDevice.getOrElse(Future.exception(graphQlError("Unable to parse device input fields"))).asScala

val MutationType: ObjectType[RootContext, Unit] = ObjectType(
  description = "The Redbubble iOS Mutation API.",
  fields[RootContext, Unit](
      name = "registerDevice",
      arguments = List(RegisterDeviceArg),
      fieldType = OptionType(RegisteredDeviceType),
      resolve = registerDevice


For contributors, a cheat sheet to making a new release:

$ git commit -m "New things" && git push
$ git tag -a v0.0.3 -m "v0.0.3"
$ git push --tags
$ ./sbt publish


Issues and pull requests are welcome. Code contributions should be aligned with the above scope to be included, and include unit tests.