Only allow request handlers on member invokers (typescript only)

src/__tests__/integration.test.ts

@@ -51,7 +51,7 @@ function createServer(spies: any) {
   const classAPI = makeClassInvoker(TestClass)
   router.get('/function', fnAPI('handle'))
   router.get('/class', classAPI('handle'))
-  router.get('/fail', fnAPI('not a method'))
+  router.get('/fail', fnAPI('not a method' as any))
   app.use(router)
 
   return new Promise((resolve, reject) => {

src/controller.ts

@@ -5,7 +5,8 @@ import {
   HttpVerbs,
   getStateAndTarget,
   IStateAndTarget,
-  IAwilixControllerBuilder
+  IAwilixControllerBuilder,
+  ClassOrFunctionReturning
 } from 'awilix-router-core'
 import { makeInvoker } from './invokers'
 import { Router } from 'express'
@@ -83,7 +84,7 @@ function _registerController(
         methodCfg.paths,
         ...methodCfg.beforeMiddleware,
         /*tslint:disable-next-line*/
-        makeInvoker(target as any)(methodName),
+        makeInvoker(target as ClassOrFunctionReturning<any>)(methodName as any),
         ...methodCfg.afterMiddleware
       )
     })

src/invokers.ts

@@ -9,10 +9,13 @@ import {
   FunctionReturning
 } from 'awilix'
 import { isClass } from 'awilix/lib/utils'
-import { NextFunction, Request, Response } from 'express'
-import { MethodName } from 'awilix-router-core'
+import { NextFunction, Request, Response, RequestHandler } from 'express'
 import assert = require('assert')
 
+export type RequestHandlerProps<T> = {
+  [K in keyof T]: T[K] extends RequestHandler ? K : never
+}[keyof T]
+
 /**
  * Creates either a function invoker or a class invoker, based on whether
  * the argument can be classified as a class or not. Uses Awilix' `isClass` utility.
@@ -82,15 +85,17 @@ export function makeResolverInvoker<T>(resolver: Resolver<T>) {
    * @param  {MethodName} methodToInvoke
    * @return {(req) => void}
    */
-  return function makeMemberInvoker(methodToInvoke: MethodName) {
+  return function makeMemberInvoker<K extends RequestHandlerProps<T>>(
+    methodToInvoke: K
+  ) {
     /**
      * The invoker middleware.
      *
      * @param  {E.Request} req
      * @param  {...*} rest
      * @return {*}
      */
-    return function memberInvoker(req: any, ...rest: any[]) {
+    return function memberInvoker(req: any, ...rest: any[]): ReturnType<T[K]> {
       const container: AwilixContainer = req.container
       const resolved: any = container.build(resolver)
       assert(