feat: Added preHandler option.

Author: ShogunPanda

README.md

@@ -26,6 +26,7 @@ Register as a plugin, optional providing any of the following options:
 - `convertResponsesValidationErrors`: Convert response validation errors to a structured human readable object. Default is to enable when `NODE_ENV` environment variable is different from `production`.
 - `allowUndeclaredResponses`: When converting response validation errors, allow responses that have no schema defined instead of throwing an error.
 - `responseValidatorCustomizer`: A function that receives a Ajv instances before compiling all response schemas. This can be used to add custom keywords, formats and so on.
+- `preHandler`: A function invoked before the error handlers that can modify the original error thrown. The function must accept the error as first argument and return the error to process.
 
 Once registered, the server will use the plugin handlers for all errors (basically, both `setErrorHandler` and `setNotFoundHandler` are called).
 

src/handlers.ts

@@ -36,6 +36,10 @@ export function handleValidationError(error: FastifyError, request: FastifyReque
 }
 
 export function handleErrors(error: FastifyError | Error, request: FastifyRequest, reply: FastifyReply): void {
+  if (request[kHttpErrorsEnhancedConfiguration]?.preHandler) {
+    error = request[kHttpErrorsEnhancedConfiguration]!.preHandler!(error)
+  }
+
   // It is a generic error, handle it
   const code = (error as NodeError).code
 

src/index.ts

@@ -21,7 +21,8 @@ export const plugin = fastifyPlugin(
       hideUnhandledErrors: options.hideUnhandledErrors ?? isProduction,
       convertValidationErrors: options.convertValidationErrors ?? true,
       responseValidatorCustomizer: options.responseValidatorCustomizer,
-      allowUndeclaredResponses: options.allowUndeclaredResponses ?? false
+      allowUndeclaredResponses: options.allowUndeclaredResponses ?? false,
+      preHandler: typeof options.preHandler === 'function' ? options.preHandler : undefined
     }
 
     instance.decorate(kHttpErrorsEnhancedConfiguration, null)

src/interfaces.ts

@@ -1,4 +1,5 @@
 import Ajv, { ValidateFunction } from 'ajv'
+import { FastifyError } from 'fastify'
 
 export const kHttpErrorsEnhancedConfiguration = Symbol('fastify-http-errors-enhanced-configuration')
 export const kHttpErrorsEnhancedResponseValidations = Symbol('fastify-http-errors-enhanced-response-validation')
@@ -8,6 +9,7 @@ export interface Configuration {
   convertValidationErrors?: boolean
   allowUndeclaredResponses?: boolean
   responseValidatorCustomizer?: (ajv: Ajv) => void
+  preHandler?: (error: FastifyError | Error) => Error
 }
 
 declare module 'fastify' {