ErrorHandler: invoke class specific toJSON transformation

README.md

@@ -691,7 +691,30 @@ There are set of prepared errors you can use:
 * NotFoundError
 * UnauthorizedError
 
-You can also create and use your own errors by extending `HttpError` class.
+
+You can also create and use your own errors by extending `HttpError` class.  
+To define the data returned to the client, you could define a toJSON method in your error.
+
+```typescript
+class DbError extends HttpError {
+    public operationName: string;
+    public args: any[];
+
+    constructor(operationName: string, args: any[] = []) {
+        super(500);
+        Object.setPrototypeOf(this, DbError.prototype);
+        this.operationName = operationName;
+        this.args = args; // can be used for internal logging
+    }
+
+    toJSON() {
+        return {
+            status: this.httpCode,
+            failedOperation: this.operationName
+        }
+    }
+}
+``` 
 
 #### Enable CORS
 

src/driver/BaseDriver.ts

@@ -150,6 +150,9 @@ export abstract class BaseDriver {
         if (!this.isDefaultErrorHandlingEnabled)
             return error;
 
+        if (typeof error.toJSON === "function")
+            return error.toJSON();
+
         let processedError: any = {};
         if (error instanceof Error) {
             const name = error.name && error.name !== "Error" ? error.name : error.constructor.name;

test/functional/express-error-handling.spec.ts

@@ -6,6 +6,7 @@ import {Middleware} from "../../src/decorator/Middleware";
 import {UseAfter} from "../../src/decorator/UseAfter";
 import {ExpressErrorMiddlewareInterface} from "../../src/driver/express/ExpressErrorMiddlewareInterface";
 import {NotFoundError} from "../../src/http-error/NotFoundError";
+import {HttpError} from "../../src/http-error/HttpError";
 const chakram = require("chakram");
 const expect = chakram.expect;
 
@@ -54,6 +55,25 @@ describe("express error handling", () => {
 
         }
 
+        class ToJsonError extends HttpError {
+            public publicData: string;
+            public secretData: string;
+
+            constructor(httpCode: number, publicMsg?: string, privateMsg?: string) {
+                super(httpCode);
+                Object.setPrototypeOf(this, ToJsonError.prototype);
+                this.publicData = publicMsg || "public";
+                this.secretData = privateMsg || "secret";
+            }
+
+            toJSON() {
+                return {
+                    status: this.httpCode,
+                    publicData: `${this.publicData} (${this.httpCode})`
+                }
+            }
+        }
+
         @JsonController()
         class ExpressErrorHandlerController {
 
@@ -97,6 +117,11 @@ describe("express error handling", () => {
                 return "1234";
             }
 
+            @Get("/stories")
+            stories() {
+                throw new ToJsonError(503, "sorry, try it again later", "impatient user");
+            }
+
         }
     });
 
@@ -154,4 +179,15 @@ describe("express error handling", () => {
             });
     });
 
+    it("should process JsonErrors by their toJSON method if it exists", () => {
+        return chakram
+            .get("http://127.0.0.1:3001/stories")
+            .then((response: any) => {
+                expect(response).to.have.status(503);
+                expect(response.body).to.have.property("status").and.equals(503);
+                expect(response.body).to.have.property("publicData").and.equals("sorry, try it again later (503)");
+                expect(response.body).to.not.have.property("secretData");
+            });
+    });
+
 });