feat: implement createRFC7807Error factory to support RFC7807

index.js

@@ -90,11 +90,39 @@ function createError (code, message, statusCode = 500, Base = Error, captureStac
   return FastifyError
 }
 
+function createRFC7807Error (
+  code,
+  message,
+  statusCode = 500,
+  opts = {},
+  Base = Error,
+  captureStackTrace = createError.captureStackTrace
+) {
+  const Err = createError(code, message, statusCode, Base, captureStackTrace)
+
+  Err.type = opts.type || 'about:blank'
+  Err.title = opts.title || 'FastifyError'
+
+  Err.prototype.toRFC7807 = function (instance = '', details = {}) {
+    return {
+      type: Err.type,
+      title: Err.title,
+      status: this.statusCode ?? statusCode,
+      detail: this.message,
+      instance,
+      code: this.code,
+      details
+    }
+  }
+  return Err
+}
+
 createError.captureStackTrace = true
 
 const FastifyErrorConstructor = createError(FastifyGenericErrorSymbol, 'Fastify Error', 500, Error)
 
 module.exports = createError
 module.exports.FastifyError = FastifyErrorConstructor
+module.exports.createRFC7807Error = createRFC7807Error
 module.exports.default = createError
 module.exports.createError = createError

test/index.test.js

@@ -1,7 +1,7 @@
 'use strict'
 
 const test = require('node:test')
-const { createError, FastifyError } = require('..')
+const { createError, FastifyError, createRFC7807Error } = require('..')
 
 test('Create error with zero parameter', (t) => {
   t.plan(6)
@@ -230,3 +230,45 @@ test('check if FastifyError is instantiable', (t) => {
   t.assert.ok(err instanceof FastifyError)
   t.assert.ok(err instanceof Error)
 })
+
+test('toRFC7807() with defaults', (t) => {
+  t.plan(1)
+
+  const E = createRFC7807Error('CODE', 'oops')
+  const e = new E()
+  const pd = e.toRFC7807('/test')
+
+  t.assert.deepStrictEqual(pd, {
+    type: 'about:blank',
+    title: 'FastifyError',
+    status: 500,
+    detail: 'oops',
+    instance: '/test',
+    code: 'CODE',
+    details: {}
+  })
+})
+
+test('toRFC7807() merges extension details', (t) => {
+  t.plan(1)
+
+  const Warning = createRFC7807Error(
+    'WARN',
+    'Threshold exceeded by %d',
+    429,
+    { type: 'https://example.net/probs/warn', title: 'Warning' }
+  )
+  const w = new Warning(7)
+
+  const pd = w.toRFC7807('/limit', { retryAfter: 60, exceeded: true })
+
+  t.assert.deepStrictEqual(pd, {
+    type: 'https://example.net/probs/warn',
+    title: 'Warning',
+    status: 429,
+    detail: 'Threshold exceeded by 7',
+    instance: '/limit',
+    code: 'WARN',
+    details: { retryAfter: 60, exceeded: true }
+  })
+})

types/index.d.ts

@@ -28,7 +28,9 @@ declare namespace createError {
   export interface FastifyError extends Error {
     code: string
     name: string
-    statusCode?: number
+    statusCode?: number,
+    toRFC7807?(instance?: string, details?: Record<string, any>): RFC7807Problem
+
   }
 
   export interface FastifyErrorConstructor<
@@ -40,6 +42,29 @@ declare namespace createError {
     readonly prototype: FastifyError & E
   }
 
+  export function createRFC7807Error<
+  C extends string,
+  SC extends number,
+  Arg extends unknown[] = [any?, any?, any?]
+> (
+    code: C,
+    message: string,
+    statusCode?: SC,
+    opts?: { type?: string; title?: string },
+    Base?: ErrorConstructor,
+    captureStackTrace?: boolean
+  ): createError.FastifyErrorConstructor<{ code: C; statusCode: SC }, Arg>
+
+  export interface RFC7807Problem {
+    type: string
+    title: string
+    status: number
+    detail: string
+    instance?: string
+    code: string
+    details?: Record<string, unknown>
+  }
+
   export const FastifyError: FastifyErrorConstructor
 
   export const createError: CreateError