Mix this trait into your REST service provider to convert between different response types and a LiftResponse. You need to define the createTag method to provide a root element for your API. You may optionally override the successAttrName, operationAttrName, and/or msgAttrName defs to control the attributes that will be applied to your root element based on the return from your API.

For example, the following code implements a simple API that takes a comma- separated string of integers and reduces them with various operations.

object CalculatorApi extends XmlApiHelper {
  // Define our root tag
  def createTag(contents : NodeSeq) : Elem = <api>{contents}</api>

  // The LiftResponses here will be converted to Box[LiftResponse]
  // via the putResponseInBox implicit conversion
  def calculator : LiftRules.DispatchPF = {
    case r @ Req(List("api","sum"), _, GetRequest) => () => doSum(r)
    case r @ Req(List("api","product"), _, GetRequest) => () => doProduct(r)
    case r @ Req(List("api","max"), _, GetRequest) => () => doMax(r)
    case r @ Req(List("api","min"), _, GetRequest) => () => doMin(r)
    case Req("api" :: _, _, _) => () => BadResponse()
  }

  // Define a common handler
  def reduceOp (operation : (Int,Int) => Int)(r : Req) : Box[Elem] = tryo {
    (r.param("args").map {
      args => <result>{args.split(",").map(_.toInt).reduceLeft(operation)}</result>
     }) ?~ "Missing args"
  } match {
    case Full(x) => x
    case f : Failure => f
    case Empty => Empty
  }

  // Using a return type of LiftResponse causes the canNodeToResponse
  // implicit to be invoked
  def doSum (r : Req) : LiftResponse = reduceOp(_ + _)(r)
  def doProduct (r : Req) : LiftResponse = reduceOp(_ * _)(r)
  def doMax (r : Req) : LiftResponse = reduceOp(_ max _)(r)
  def doMin (r : Req) : LiftResponse = reduceOp(_ min _)(r)
}

With this API, the URL

http://foo.com/api/sum?args=1,2,3,4,5

would return

<api operation="sum" success="true"><result>15</result></api>

http://foo.com/api/sum?args=1,2,3,4,5 return

<api operation="sum" success="true"><result>15</result></api>