Return exact response/header? - scala

Question

From the client-side of a webapp, I hit a server-side route which is just a wrapper for a third-party API. Using dispatch, I am trying to make that server-side request return the exact header and response of the third-party API to the client-side AJAX call.
When I do this:
val req = host("third-pary.api.com, 80)
val post = req.as("user", "pass") / "route" << Map("key" -> "akey", "val" -> "aval")
Http(post > as.String)
I always see a 200 response returned to the AJAX call (kind of expectedly). I have seen an Either syntax used, but I'm really more of an Any, as it's just the exact response and header. How would this be written?
I should mention I'm using Scalatra on the server-side, so the local route is:
post("/route") {
}
EDIT:
Here is the suggested Either matching example, which I'm playing with, but the match syntax doesn't make sense - I don't care if there is an error, I just want to return it. Also, I can't seem to get the BODY returned with this method.
val asHeaders = as.Response { response =>
println("BODY: " + response.getResponseBody())
scala.collection.JavaConverters.mapAsScalaMapConverter(
response.getHeaders).asScala.toMap.mapValues(_.asScala.toList)
}
val response: Either[Throwable, Map[String, List[String]]] =
Http(post > asHeaders).either()
response match {
case Left(wrong) =>
println("Left: " + wrong.getMessage())
// return Action with header + body
case Right(good) =>
println("Right: " + good)
// return Action with header + body
}
Ideally, the solutions returns the Scalatra ActionResult(responseStatus(status, reason), body, headers).

Answer 1

It's actually very easy to get response headers while using Dispatch. For example with 0.9.4:
import dispatch._
import scala.collection.JavaConverters._
val headers: java.util.Map[String, java.util.List[String]] = Http(
url("http://www.google.com")
)().getHeaders
And now, for example:
scala> headers.asScala.mapValues(_.asScala).foreach {
| case (k, v) => println(k + ": " + v)
| }
X-Frame-Options: Buffer(SAMEORIGIN)
Transfer-Encoding: Buffer(chunked)
Date: Buffer(Fri, 30 Nov 2012 20:42:45 GMT)
...
If you do this often it's better to encapsulate it, like this, for example:
val asHeaders = as.Response { response =>
scala.collection.JavaConverters.mapAsScalaMapConverter(
response.getHeaders
).asScala.toMap.mapValues(_.asScala.toList)
}
Now you can write the following:
val response: Either[Throwable, Map[String, List[String]]] =
Http(url("http://www.google.com") OK asHeaders).either()
And you've got error checking, nice immutable collections, etc.

Answer 2

We needed the response body of failed requests to an API, so we came up with this solution:
Define your own ApiHttpError class with code and body (for the body text):
case class ApiHttpError(code: Int, body: String)
extends Exception("Unexpected response status: %d".format(code))
Define OkWithBodyHandler similar to what is used in the source of displatch:
class OkWithBodyHandler[T](f: Response => T) extends AsyncCompletionHandler[T] {
def onCompleted(response: Response) = {
if (response.getStatusCode / 100 == 2) {
f(response)
} else {
throw ApiHttpError(response.getStatusCode, response.getResponseBody)
}
}
}
Now, near your call to the code that might throw and exception (calling API), add implicit override to the ToupleBuilder (again similar to the source code) and call OkWithBody on request:
class MyApiService {
implicit class MyRequestHandlerTupleBuilder(req: Req) {
def OKWithBody[T](f: Response => T) =
(req.toRequest, new OkWithBodyHandler(f))
}
def callApi(request: Req) = {
Http(request OKWithBody as.String).either
}
}
From now on, fetching either will give you the [Throwable, String] (using as.String), and the Throwable is our ApiHttpError with code and body.
Hope it helped.