Add request preprocessor function

Author: mduesterhoeft

src/main/kotlin/com/github/mduesterhoeft/router/RequestHandler.kt

@@ -27,8 +27,10 @@ abstract class RequestHandler : RequestHandler<APIGatewayProxyRequestEvent, APIG
             log.info("match result for route '$routerFunction' is '$matchResult'")
             if (matchResult.match) {
                 val handler: HandlerFunction<Any, Any> = routerFunction.handler
-                val request = deserializeRequest(handler, input)
-                val response = handler(Request(input, request))
+                val requestBody = deserializeRequest(handler, input)
+                val request = Request(input, requestBody)
+                router.requestPreprocessor(request)
+                val response = handler(request)
                 return createResponse(input, response)
             }
 

src/main/kotlin/com/github/mduesterhoeft/router/Router.kt

@@ -9,6 +9,8 @@ class Router {
     var defaultConsuming = setOf("application/json", "application/x-protobuf")
     var defaultProducing = setOf("application/json", "application/x-protobuf")
 
+    var requestPreprocessor: (Request<*>) -> Unit = { _ -> Unit }
+
     fun <I, T> GET(pattern: String, handlerFunction: HandlerFunction<I, T>) =
         RequestPredicate(
             method = "GET",
@@ -63,6 +65,8 @@ class Router {
     // the default content types the HandlerFunctions of this router can handle
     fun defaultConsuming(contentTypes: Set<String>): Router = this.also { defaultConsuming = contentTypes }
 
+    fun withPreprocessor(preprocessorFunction: (Request<*>) -> Unit): Router = this.also { requestPreprocessor = preprocessorFunction }
+
     companion object {
         fun router(routes: Router.() -> Unit) = Router().apply(routes)
     }