From 4ad7ad368c3de980438c0723009c353c94f3b0ad Mon Sep 17 00:00:00 2001
From: Philip Molares <philip.molares@udo.edu>
Date: Mon, 17 Jan 2022 09:03:01 +0100
Subject: [PATCH] feat: add error-mapping

The ErrorExceptionMapping class maps internal error to nestjs's appropriate HttpException.
The object returned by those HttpExceptions is now changed to include the name of the intern error code and error message instead of statusCode and error message as is default. This makes it possible to more easily programmatically distinguish between two errors that map to the same HttpException and only differ in the error message.
The statusCode was unnecessary, because any user of the api gets this information already by which HttpException was used.

Signed-off-by: Philip Molares <philip.molares@udo.edu>
---
 src/errors/error-mapping.ts         | 89 +++++++++++++++++++++++++++++
 src/errors/http-exception-object.ts | 20 +++++++
 2 files changed, 109 insertions(+)
 create mode 100644 src/errors/error-mapping.ts
 create mode 100644 src/errors/http-exception-object.ts

diff --git a/src/errors/error-mapping.ts b/src/errors/error-mapping.ts
new file mode 100644
index 000000000..59967bf54
--- /dev/null
+++ b/src/errors/error-mapping.ts
@@ -0,0 +1,89 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import {
+  ArgumentsHost,
+  BadRequestException,
+  ConflictException,
+  InternalServerErrorException,
+  NotFoundException,
+  UnauthorizedException,
+} from '@nestjs/common';
+import { HttpException } from '@nestjs/common/exceptions/http.exception';
+import { BaseExceptionFilter } from '@nestjs/core';
+
+import {
+  buildHttpExceptionObject,
+  HttpExceptionObject,
+} from './http-exception-object';
+
+type HttpExceptionConstructor = (object: HttpExceptionObject) => HttpException;
+
+const mapOfHedgeDocErrorsToHttpErrors: Map<string, HttpExceptionConstructor> =
+  new Map([
+    ['NotInDBError', (object): HttpException => new NotFoundException(object)],
+    [
+      'AlreadyInDBError',
+      (object): HttpException => new ConflictException(object),
+    ],
+    [
+      'ForbiddenIdError',
+      (object): HttpException => new BadRequestException(object),
+    ],
+    ['ClientError', (object): HttpException => new BadRequestException(object)],
+    [
+      'PermissionError',
+      (object): HttpException => new UnauthorizedException(object),
+    ],
+    [
+      'TokenNotValidError',
+      (object): HttpException => new UnauthorizedException(object),
+    ],
+    [
+      'TooManyTokensError',
+      (object): HttpException => new BadRequestException(object),
+    ],
+    [
+      'PermissionsUpdateInconsistentError',
+      (object): HttpException => new BadRequestException(object),
+    ],
+    [
+      'MediaBackendError',
+      (object): HttpException => new InternalServerErrorException(object),
+    ],
+    [
+      'PrimaryAliasDeletionForbiddenError',
+      (object): HttpException => new BadRequestException(object),
+    ],
+    [
+      'InvalidCredentialsError',
+      (object): HttpException => new UnauthorizedException(object),
+    ],
+    [
+      'NoLocalIdentityError',
+      (object): HttpException => new BadRequestException(object),
+    ],
+  ]);
+
+export class ErrorExceptionMapping extends BaseExceptionFilter<Error> {
+  catch(error: Error, host: ArgumentsHost): void {
+    super.catch(ErrorExceptionMapping.transformError(error), host);
+  }
+
+  private static transformError(error: Error): Error {
+    const httpExceptionConstructor = mapOfHedgeDocErrorsToHttpErrors.get(
+      error.name,
+    );
+    if (httpExceptionConstructor === undefined) {
+      // We don't know how to map this error and just leave it be
+      return error;
+    }
+    const httpExceptionObject = buildHttpExceptionObject(
+      error.name,
+      error.message,
+    );
+    return httpExceptionConstructor(httpExceptionObject);
+  }
+}
diff --git a/src/errors/http-exception-object.ts b/src/errors/http-exception-object.ts
new file mode 100644
index 000000000..2f9a399ce
--- /dev/null
+++ b/src/errors/http-exception-object.ts
@@ -0,0 +1,20 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+export interface HttpExceptionObject {
+  name: string;
+  message: string;
+}
+
+export function buildHttpExceptionObject(
+  name: string,
+  message: string,
+): HttpExceptionObject {
+  return {
+    name: name,
+    message: message,
+  };
+}