Play framework filter that modifies json request and response

Question

I'll appreciate if someone can throw pointers on how to modify the following play framework logging filter (ref. play filters ) to achieve the following:

• Print and modify the incoming json request body and http headers (eg, for POST, PUT, & PATCH)
• Print and modify the outgoing json response body and http headers
• A modification example can be injecting/replacing some token strings in the request and response body, eg,
• REQUEST Json: {'a': 'REPLACE_ME', 'b': 'REPLACE_ME_TOO', 'c':'something'}
• RESPONSE Json: {'A': 'REPLACE_ME', 'Bb': 'REPLACE_ME_TOO', 'C':'anything'}

---

import play.api.Logger
import play.api.mvc._
import play.api.libs.concurrent.Execution.Implicits.defaultContext

object LoggingFilter extends EssentialFilter {
  def apply(nextFilter: EssentialAction) = new EssentialAction {
    def apply(requestHeader: RequestHeader) = {
      val startTime = System.currentTimeMillis
      nextFilter(requestHeader).map { result =>
        val endTime = System.currentTimeMillis
        val requestTime = endTime - startTime
        Logger.info(s"${requestHeader.method} ${requestHeader.uri}" +
          s" took ${requestTime}ms and returned ${result.header.status}")
        result.withHeaders("Request-Time" -> requestTime.toString)
      }
    }
  }
}

---

So far I have tried the following solution which is clearly ugly and brutal as it contains blocking calls and cryptic operators. I am still not sure how to re-inject the modified request body. (The presented solution incorporates code from 2 and 3 .)

import play.api.libs.iteratee._
import play.api.mvc._

import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.{Await, Future}
import scala.concurrent.duration.Duration

class ReqResFilter extends EssentialFilter {

  def apply(next: EssentialAction) = new EssentialAction {
    def apply(requestHeader: RequestHeader): Iteratee[Array[Byte], Result] = {
      modifyRequest(next, requestHeader).map { result => modifyResponse(result)}
    }
  }

  def bytesToString: Enumeratee[Array[Byte], String] = Enumeratee.map[Array[Byte]] { bytes => new String(bytes)}

  def modifyRequest(nextA: EssentialAction, request: RequestHeader): Iteratee[Array[Byte], Result] = {

    def step(body: Array[Byte], nextI: Iteratee[Array[Byte], Result])(i: Input[Array[Byte]]):
    Iteratee[Array[Byte], Result] = i match {
      case Input.EOF =>
        val requestBody = new String(body, "utf-8")
        val modRequestBody = requestBody.replaceAll("REPLACE_ME", "1224")
        println(s"modifyRequest:: Here is the request body ${modRequestBody}")
        Iteratee.flatten(nextI.feed(Input.EOF))
      case Input.Empty =>
        Cont[Array[Byte], Result](step(body, nextI) _)
      case Input.El(e) =>
        val curBody = Array.concat(body, e)
        Cont[Array[Byte], Result](step(curBody, Iteratee.flatten(nextI.feed(Input.El(e)))) _)
    }

    val nextIteratee: Iteratee[Array[Byte], Result] = nextA(request)

    Cont[Array[Byte], Result](i => step(Array(), nextIteratee)(i))
  }

  def modifyResponse(result: Result): Result = {
    val responseBodyFuture: Future[String] = result.body |>>> bytesToString &>> Iteratee.consume[String]()
    val responseBody = Await.result(responseBodyFuture, Duration.Inf)
    val modResponseBody = responseBody.replaceAll("REPLACE_ME", "1224")
    println(s"modifyResponse:: Here is the response body ${modResponseBody}")
    new Result(result.header, Enumerator(modResponseBody.getBytes)).withHeaders("New-Header" -> "1234")
  }
}

Answer 1

Well since there are no solutions posted here let me add one solution. To make it work, I rewrote step() in modifyRequest() as follows:

def step(body: Array[Byte], nextI: Iteratee[Array[Byte], Result])(i: Input[Array[Byte]]):
Iteratee[Array[Byte], Result] = i match {
  case Input.EOF =>
    val requestBody = new String(body, "utf-8")
    val modRequestBody = requestBody.replaceAll("REPLACE_ME", "1224")
    println(s"modifyRequest:: Here is the request body ${modRequestBody}")
    Iteratee.flatten(nextI.feed(Input.El(modRequestBody.getBytes)))
  case Input.Empty =>
    Cont[Array[Byte], Result](step(body, nextI) _)
  case Input.El(e) =>
    val curBody = Array.concat(body, e)
    Cont[Array[Byte], Result](step(curBody, nextI) _)
}

The change is still blocking in nature as it buffers the incoming request. If someone has better solution please do post. Thanks.