fix: Retain status codes when combining errors

src/util/CompositeAsyncHandler.ts

@@ -1,4 +1,6 @@
 import type { AsyncHandler } from './AsyncHandler';
+import { HttpError } from './errors/HttpError';
+import { InternalServerError } from './errors/InternalServerError';
 import { UnsupportedHttpError } from './errors/UnsupportedHttpError';
 
 /**
@@ -70,7 +72,7 @@ export class CompositeAsyncHandler<TIn, TOut> implements AsyncHandler<TIn, TOut>
    * @returns A promise resolving to a handler that supports the data or otherwise rejecting.
    */
   private async findHandler(input: TIn): Promise<AsyncHandler<TIn, TOut>> {
-    const errors: Error[] = [];
+    const errors: HttpError[] = [];
 
     for (const handler of this.handlers) {
       try {
@@ -78,16 +80,28 @@ export class CompositeAsyncHandler<TIn, TOut> implements AsyncHandler<TIn, TOut>
 
         return handler;
       } catch (error: unknown) {
-        if (error instanceof Error) {
+        if (error instanceof HttpError) {
           errors.push(error);
+        } else if (error instanceof Error) {
+          errors.push(new InternalServerError(error.message));
         } else {
-          errors.push(new Error('Unknown error.'));
+          errors.push(new InternalServerError('Unknown error.'));
         }
       }
     }
 
     const joined = errors.map((error: Error): string => error.message).join(', ');
+    const message = `No handler supports the given input: [${joined}].`;
 
-    throw new UnsupportedHttpError(`No handler supports the given input: [${joined}].`);
+    // Check if all errors have the same status code
+    if (errors.every((error): boolean => error.statusCode === errors[0].statusCode)) {
+      throw new HttpError(errors[0].statusCode, errors[0].name, message);
+    }
+
+    // Find the error range (4xx or 5xx)
+    if (errors.some((error): boolean => error.statusCode >= 500)) {
+      throw new InternalServerError(message);
+    }
+    throw new UnsupportedHttpError(message);
   }
 }

src/util/errors/HttpError.ts

@@ -1,8 +1,8 @@
 /**
- * An abstract class for all errors that could be thrown by Solid.
+ * A class for all errors that could be thrown by Solid.
  * All errors inheriting from this should fix the status code thereby hiding the HTTP internals from other components.
  */
-export abstract class HttpError extends Error {
+export class HttpError extends Error {
   public statusCode: number;
 
   /**
@@ -11,7 +11,7 @@ export abstract class HttpError extends Error {
    * @param name - Error name. Useful for logging and stack tracing.
    * @param message - Message to be thrown.
    */
-  protected constructor(statusCode: number, name: string, message?: string) {
+  public constructor(statusCode: number, name: string, message?: string) {
     super(message);
     this.statusCode = statusCode;
     this.name = name;

src/util/errors/InternalServerError.ts

@@ -0,0 +1,9 @@
+import { HttpError } from './HttpError';
+/**
+ * A generic error message, given when an unexpected condition was encountered and no more specific message is suitable.
+ */
+export class InternalServerError extends HttpError {
+  public constructor(message?: string) {
+    super(500, 'InternalServerError', message);
+  }
+}

test/unit/util/CompositeAsyncHandler.test.ts

@@ -1,5 +1,7 @@
 import type { AsyncHandler } from '../../../src/util/AsyncHandler';
 import { CompositeAsyncHandler } from '../../../src/util/CompositeAsyncHandler';
+import { HttpError } from '../../../src/util/errors/HttpError';
+import { UnsupportedHttpError } from '../../../src/util/errors/UnsupportedHttpError';
 import { StaticAsyncHandler } from '../../util/StaticAsyncHandler';
 
 describe('A CompositeAsyncHandler', (): void => {
@@ -81,5 +83,44 @@ describe('A CompositeAsyncHandler', (): void => {
 
       await expect(handler.handleSafe(null)).rejects.toThrow('[Not supported., Not supported.]');
     });
+
+    it('throws an error with matching status code if all handlers threw the same.', async(): Promise<void> => {
+      handlerTrue.canHandle = async(): Promise<void> => {
+        throw new HttpError(401, 'UnauthorizedHttpError');
+      };
+      const handler = new CompositeAsyncHandler([ handlerTrue, handlerTrue ]);
+
+      await expect(handler.canHandle(null)).rejects.toMatchObject({
+        statusCode: 401,
+        name: 'UnauthorizedHttpError',
+      });
+    });
+
+    it('throws an internal server error if one of the handlers threw one.', async(): Promise<void> => {
+      handlerTrue.canHandle = async(): Promise<void> => {
+        throw new HttpError(401, 'UnauthorizedHttpError');
+      };
+      handlerFalse.canHandle = async(): Promise<void> => {
+        throw new Error('Server is crashing!');
+      };
+      const handler = new CompositeAsyncHandler([ handlerTrue, handlerFalse ]);
+
+      await expect(handler.canHandle(null)).rejects.toMatchObject({
+        statusCode: 500,
+        name: 'InternalServerError',
+      });
+    });
+
+    it('throws an UnsupportedHttpError if handlers throw different errors.', async(): Promise<void> => {
+      handlerTrue.canHandle = async(): Promise<void> => {
+        throw new HttpError(401, 'UnauthorizedHttpError');
+      };
+      handlerFalse.canHandle = async(): Promise<void> => {
+        throw new HttpError(415, 'UnsupportedMediaTypeHttpError');
+      };
+      const handler = new CompositeAsyncHandler([ handlerTrue, handlerFalse ]);
+
+      await expect(handler.canHandle(null)).rejects.toThrow(UnsupportedHttpError);
+    });
   });
 });