Documentation (v4.2.1)

Errors

Error Handling In Node.js

Uncaught Errors

In Node.js, uncaught errors are likely to cause memory leaks, file descriptor leaks, and other major production issues. Domains were a failed attempt to fix this.

Given that it is not possible to process all uncaught errors sensibly, the best way to deal with them is to crash.

Catching Errors In Promises

If you are using promises, you should attach a .catch() handler synchronously.

Errors In Fastify

Fastify follows an all-or-nothing approach and aims to be lean and optimal as much as possible. The developer is responsible for making sure that the errors are handled properly.

Errors In Input Data

Most errors are a result of unexpected input data, so we recommend validating your input data against a JSON schema.

Catching Uncaught Errors In Fastify

Fastify tries to catch as many uncaught errors as it can without hindering performance. This includes:

  1. synchronous routes, e.g. app.get('/', () => { throw new Error('kaboom') })
  2. async routes, e.g. app.get('/', async () => { throw new Error('kaboom') })

The error in both cases will be caught safely and routed to Fastify's default error handler for a generic 500 Internal Server Error response.

To customize this behavior you should use setErrorHandler.

Errors In Fastify Lifecycle Hooks And A Custom Error Handler

From the Hooks documentation:

If you get an error during the execution of your hook, just pass it to done() and Fastify will automatically close the request and send the appropriate error code to the user.

When a custom error handler has been defined through setErrorHandler, the custom error handler will receive the error passed to the done() callback (or through other supported automatic error handling mechanisms). If setErrorHandler has been used multiple times to define multiple handlers, the error will be routed to the most precedent handler defined within the error encapsulation context. Error handlers are fully encapsulated, so a setErrorHandler call within a plugin will limit the error handler to that plugin's context.

The root error handler is Fastify's generic error handler. This error handler will use the headers and status code in the Error object, if they exist. The headers and status code will not be automatically set if a custom error handler is provided.

Some things to consider in your custom error handler:

  • you can reply.send(data), which will behave as it would in regular route handlers

    • objects are serialized, triggering the preSerialization lifecycle hook if you have one defined
    • strings, buffers, and streams are sent to the client, with appropriate headers (no serialization)
  • You can throw a new error in your custom error handler - errors (new error or the received error parameter re-thrown) - will call the parent errorHandler.

    • onError hook will be triggered once only for the first error being thrown.
    • an error will not be triggered twice from a lifecycle hook - Fastify internally monitors the error invocation to avoid infinite loops for errors thrown in the reply phases of the lifecycle. (those after the route handler)

Fastify Error Codes

FST_ERR_BAD_URL

The router received an invalid url.

FST_ERR_DUPLICATED_ROUTE

The HTTP method already has a registered controller for that URL

FST_ERR_CTP_ALREADY_PRESENT

The parser for this content type was already registered.

FST_ERR_CTP_BODY_TOO_LARGE

The request body is larger than the provided limit.

This setting can be defined in the Fastify server instance: bodyLimit

FST_ERR_CTP_EMPTY_TYPE

The content type cannot be an empty string.

FST_ERR_CTP_INVALID_CONTENT_LENGTH

Request body size did not match Content-Length.

FST_ERR_CTP_INVALID_HANDLER

An invalid handler was passed for the content type.

FST_ERR_CTP_INVALID_MEDIA_TYPE

The received media type is not supported (i.e. there is no suitable Content-Type parser for it).

FST_ERR_CTP_INVALID_PARSE_TYPE

The provided parse type is not supported. Accepted values are string or buffer.

FST_ERR_CTP_INVALID_TYPE

The Content-Type should be a string.

FST_ERR_DEC_ALREADY_PRESENT

A decorator with the same name is already registered.

FST_ERR_DEC_MISSING_DEPENDENCY

The decorator cannot be registered due to a missing dependency.

FST_ERR_HOOK_INVALID_HANDLER

The hook callback must be a function.

FST_ERR_HOOK_INVALID_TYPE

The hook name must be a string.

FST_ERR_LOG_INVALID_DESTINATION

The logger accepts either a 'stream' or a 'file' as the destination.

FST_ERR_PROMISE_NOT_FULFILLED

A promise may not be fulfilled with 'undefined' when statusCode is not 204.

FST_ERR_REP_ALREADY_SENT

A response was already sent.

FST_ERR_REP_INVALID_PAYLOAD_TYPE

Reply payload can be either a string or a Buffer.

FST_ERR_SCH_ALREADY_PRESENT

A schema with the same $id already exists.

FST_ERR_SCH_MISSING_ID

The schema provided does not have $id property.

FST_ERR_SCH_SERIALIZATION_BUILD

The JSON schema provided for serialization of a route response is not valid.

FST_ERR_SCH_VALIDATION_BUILD

The JSON schema provided for validation to a route is not valid.

FST_ERR_SEND_INSIDE_ONERR

You cannot use send inside the onError hook.

FST_ERR_SEND_UNDEFINED_ERR

Undefined error has occurred.

FST_ERR_PLUGIN_NOT_VALID

Plugin must be a function or a promise.

FST_ERR_PLUGIN_TIMEOUT

Plugin did not start in time. Default timeout (in millis): 10000

FST_ERR_HOOK_TIMEOUT

A callback for a hook timed out

FST_ERR_ROOT_PLG_BOOTED

Root plugin has already booted (mapped directly from avvio)

FST_ERR_PARENT_PLUGIN_BOOTED

Impossible to load plugin because the parent (mapped directly from avvio)

FST_ERR_PLUGIN_CALLBACK_NOT_FN

Callback for a hook is not a function (mapped directly from avvio)