Support async operation handler resolver (#921)

- Let users define operationHandlers.resolver as a synchronous or
  asynchronous function that returns a request handler
- Make installOperationHandlers and asynchronous function that awaits a
  resolver promise (automatically wraps resolver with promise if needed)
- Update operation handlers middleware to handle an async
  installOperationHandlers.

src/framework/types.ts

@@ -1,7 +1,8 @@
 import * as ajv from 'ajv';
 import * as multer from 'multer';
-import { FormatsPluginOptions, FormatOptions } from 'ajv-formats';
-import { Request, Response, NextFunction } from 'express';
+import { FormatsPluginOptions } from 'ajv-formats';
+import { Request, Response, NextFunction, RequestHandler } from 'express';
+import { RouteMetadata } from './openapi.spec.loader';
 export { OpenAPIFrameworkArgs };
 
 export type BodySchema =
@@ -63,7 +64,11 @@ export type ValidateSecurityOpts = {
 
 export type OperationHandlerOptions = {
   basePath: string;
-  resolver: Function;
+  resolver: (
+    handlersPath: string,
+    route: RouteMetadata,
+    apiDoc: OpenAPIV3.Document,
+  ) => RequestHandler | Promise<RequestHandler>;
 };
 
 export type Format = {

src/openapi.validator.ts

@@ -221,11 +221,8 @@ export class OpenApiValidator {
       middlewares.push(function operationHandlersMiddleware(req, res, next) {
         if (router) return router(req, res, next);
         return pContext
-          .then(
-            ({ context }) =>
-              (router = self.installOperationHandlers(req.baseUrl, context)),
-          )
-          .then((router) => router(req, res, next))
+          .then(({context}) => self.installOperationHandlers(req.baseUrl, context))
+          .then((installedRouter) => (router = installedRouter)(req, res, next))
           .catch(next);
       });
     }
@@ -304,7 +301,7 @@ export class OpenApiValidator {
     ).validate();
   }
 
-  installOperationHandlers(baseUrl: string, context: OpenApiContext): Router {
+  async installOperationHandlers(baseUrl: string, context: OpenApiContext): Promise<Router> {
     const router = express.Router({ mergeParams: true });
 
     this.installPathParams(router, context);
@@ -324,10 +321,8 @@ export class OpenApiValidator {
           expressRoute.indexOf(baseUrl) === 0
             ? expressRoute.substring(baseUrl.length)
             : expressRoute;
-        router[method.toLowerCase()](
-          path,
-          resolver(basePath, route, context.apiDoc),
-        );
+        const handler = await resolver(basePath, route, context.apiDoc);
+        router[method.toLowerCase()](path, handler);
       }
     }
     return router;