feat: exception handler middleware (VF-000) (#70)

* feat: exception handler middleware (VF-000)

* feat: remove previous unused ExceptionHandler

* refactor: organize formatters

* refactor: review feedback

* fix: make types work

Author: trs

package.json

@@ -13,7 +13,6 @@
   },
   "dependencies": {
     "@types/chai": "^4.2.16",
-    "@types/express": "^4.17.11",
     "@types/ioredis": "^4.26.4",
     "@types/lodash": "^4.14.168",
     "@types/luxon": "^1.26.4",
@@ -22,7 +21,7 @@
     "@voiceflow/verror": "^1.1.0",
     "chai": "^4.3.4",
     "dotenv": "^10.0.0",
-    "express": "^4.17.1",
+    "http-errors": "^2.0.0",
     "http-status": "^1.4.2",
     "lodash": "^4.17.11",
     "luxon": "^1.21.3",
@@ -34,6 +33,8 @@
     "@istanbuljs/nyc-config-typescript": "1.0.2",
     "@types/axios": "^0.14.0",
     "@types/chai-as-promised": "^7.1.4",
+    "@types/express": "^4.17.13",
+    "@types/http-errors": "^1.8.2",
     "@types/mocha": "9.1.0",
     "@types/supertest": "^2.0.11",
     "@voiceflow/commitlint-config": "2.0.0",
@@ -49,6 +50,7 @@
     "depcheck": "1.4.3",
     "eslint": "^7.32.0",
     "eslint-output": "^3.0.1",
+    "express": "^4.17.3",
     "express-validator": "^6.10.1",
     "fixpack": "^4.0.0",
     "husky": "^4.3.8",
@@ -72,6 +74,7 @@
   "license": "ISC",
   "main": "build/index.js",
   "peerDependencies": {
+    "@types/express": "^4.17.13",
     "@voiceflow/common": "^7.2.0",
     "express-validator": "^6.3.0"
   },

src/exceptionHandler.ts

@@ -1,6 +1,5 @@
 export * from './clients';
 export * from './env';
-export { default as ExceptionHandler } from './exceptionHandler';
 export { default as FixtureGenerator } from './fixtureGenerator';
 export * from './middlewares';
 export { default as ResponseBuilder } from './responseBuilder';

src/index.ts

@@ -0,0 +1,13 @@
+import { HttpError, isHttpError } from 'http-errors';
+
+import type { ExceptionFormatter } from '../types';
+
+export { isHttpError };
+
+export const formatHttpError: ExceptionFormatter<HttpError> = (err) => {
+  return {
+    statusCode: err.statusCode,
+    name: err.name,
+    message: err.message,
+  };
+};

src/middlewares/exception/formatters/httpError.ts

@@ -0,0 +1,25 @@
+import VError from '@voiceflow/verror';
+
+import type { ExceptionFormat } from '../types';
+import { formatHttpError, isHttpError } from './httpError';
+import { formatJavascriptError, isJavascriptError } from './jsError';
+import { formatVError, isVError } from './vError';
+
+export const formatError = (err: unknown): ExceptionFormat => {
+  let exception: ExceptionFormat = {
+    statusCode: VError.HTTP_STATUS.INTERNAL_SERVER_ERROR,
+    name: 'UnknownError',
+    message: 'Unknown error',
+  };
+
+  if (isVError(err)) exception = mergeExceptionResult(exception, formatVError(err));
+  else if (isHttpError(err)) exception = mergeExceptionResult(exception, formatHttpError(err));
+  else if (isJavascriptError(err)) exception = mergeExceptionResult(exception, formatJavascriptError(err));
+
+  return exception;
+};
+
+export const mergeExceptionResult = (baseException: ExceptionFormat, exception: Partial<ExceptionFormat>) => ({
+  ...baseException,
+  ...exception,
+});

src/middlewares/exception/formatters/index.ts

@@ -0,0 +1,12 @@
+import { types } from 'util';
+
+import type { ExceptionFormatter } from '../types';
+
+export const isJavascriptError = types.isNativeError;
+
+export const formatJavascriptError: ExceptionFormatter<Error> = (err) => {
+  return {
+    name: err.name,
+    message: err.message,
+  };
+};

src/middlewares/exception/formatters/jsError.ts

@@ -0,0 +1,13 @@
+import VError from '@voiceflow/verror';
+
+import type { ExceptionFormatter } from '../types';
+
+export const isVError = (err: unknown): err is VError => err != null && err instanceof VError;
+
+export const formatVError: ExceptionFormatter<VError> = (err) => {
+  return {
+    statusCode: err.code,
+    name: err.name,
+    message: err.message,
+  };
+};

src/middlewares/exception/formatters/vError.ts

@@ -0,0 +1,19 @@
+import type { NextFunction, Request, Response } from 'express';
+
+import { AbstractMiddleware } from '../../types';
+import { formatError } from './formatters';
+
+export class ExceptionMiddleware extends AbstractMiddleware<never, never> {
+  public constructor() {
+    super(undefined as never, undefined as never);
+  }
+
+  public handleError(err: unknown, req: Request, res: Response, _next: NextFunction): void {
+    const { statusCode, ...body } = formatError(err);
+
+    res.status(statusCode).send({
+      ...body,
+      requestID: req.id.toString(),
+    });
+  }
+}

src/middlewares/exception/index.ts

@@ -0,0 +1,7 @@
+export interface ExceptionFormat {
+  statusCode: number;
+  name: string;
+  message: string;
+}
+
+export type ExceptionFormatter<T> = (err: T) => Partial<ExceptionFormat>;

src/middlewares/exception/types.ts

@@ -1 +1,2 @@
+export * from './exception';
 export * from './rateLimit';