Scala Dispatch library: how to handle connection failure or timeout? - scala

Question

I've been using the Databinder Dispatch library in a client for a simple REST-ish API. I know how to detect if I get an HTTP response with an error status:
Http x (request) {
case (200, _, _, content) => successResult(content())
case (404, _, _, _) => notFoundErrorResult
case (_, _, _, _) => genericErrorResult
}
But how can I distinguish an error response from a failure to get any response at all, because of an invalid domain or failure to connect? And is there any way to implement a timeout while still using synchronous semantics? If there's anything relevant in the API, I've missed it.

Answer 1

There is also a more elegant way to configure client using Http.configure method which receives Builder => Builder function as an argument:
val http = Http.configure(_.setAllowPoolingConnection(true).setConnectionTimeoutInMs(5000))

Answer 2

The Periodic Table tells us that >! sets up an exception listener and a recent mailing list thread explains how to set a timeout.
All together, then, you might do something like:
val http = new dispatch.Http {
import org.apache.http.params.CoreConnectionPNames
client.getParams.setParameter(CoreConnectionPNames.CONNECTION_TIMEOUT, 2000)
client.getParams.setParameter(CoreConnectionPNames.SO_TIMEOUT, 5000)
}
http(req >! {
case e => // ...
})
Note that I haven't tested this...

Answer 3

In case you are using Dispatch reboot (with AsyncHttpClient as the underlying library) this is how you'd set the client configuration:
val myHttp = new dispatch.Http {
import com.ning.http.client._
val builder = new AsyncHttpClientConfig.Builder()
builder.setCompressionEnabled(true)
.setAllowPoolingConnection(true)
.setRequestTimeoutInMs(5000)
override lazy val client = new AsyncHttpClient(builder.build())
}
and then just use this new object as you'd otherwise use http:
myHttp((url(baseUrl) <<? args) OK as.xml.Elem).either