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.
If you are using promises, you should attach a .catch() handler synchronously.
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.
Most errors are a result of unexpected input data, so we recommend validating your input data against a JSON schema.
Fastify tries to catch as many uncaught errors as it can without hindering performance. This includes:
- synchronous routes, e.g.
app.get('/', () => { throw new Error('kaboom') }) asyncroutes, 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.
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
preSerializationlifecycle hook if you have one defined - strings, buffers, and streams are sent to the client, with appropriate headers (no serialization)
- objects are serialized, triggering the
-
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.onErrorhook 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)
You can access errorCodes for mapping:
// ESM
import { errorCodes } from 'fastify'
// CommonJs
const errorCodes = require('fastify').errorCodesFor example:
const Fastify = require('./fastify')
// Instantiate the framework
const fastify = Fastify({
logger: true
})
// Declare a route
fastify.get('/', function (request, reply) {
reply.code('bad status code').send({ hello: 'world' })
})
fastify.setErrorHandler(function (error, request, reply) {
if (error instanceof Fastify.errorCodes.FST_ERR_BAD_STATUS_CODE) {
// Log error
this.log.error(error)
// Send error response
reply.status(500).send({ ok: false })
}
})
// Run the server!
fastify.listen({ port: 3000 }, function (err, address) {
if (err) {
fastify.log.error(err)
process.exit(1)
}
// Server is now listening on ${address}
})404 Not Found.
The parser for this content type was already registered.
The Content-Type should be a string.
The content type cannot be an empty string.
An invalid handler was passed for the content type.
The provided parse type is not supported. Accepted values are string or
buffer.
The request body is larger than the provided limit.
This setting can be defined in the Fastify server instance:
bodyLimit
The received media type is not supported (i.e. there is no suitable
Content-Type parser for it).
Request body size did not match Content-Length.
Body cannot be empty when content-type is set to application/json.
A decorator with the same name is already registered.
The dependencies of decorator must be of type Array.
The decorator cannot be registered due to a missing dependency.
The decorator cannot be added after start.
The hook name must be a string.
The hook callback must be a function.
You must register a plugin for handling middlewares,
visit Middleware for more info.
A callback for a hook timed out
The logger accepts either a 'stream' or a 'file' as the destination.
Reply payload can be either a string or a Buffer.
A response was already sent.
The only possible value for reply.sent is true.
You cannot use send inside the onError hook.
Undefined error has occurred.
Called reply with an invalid status code.
Called reply.trailer with an invalid header name.
Called reply.trailer with an invalid type. Expected a function.
Missing serialization function.
Invalid validation invocation. Missing validation function for HTTP part nor schema provided.
The schema provided does not have $id property.
A schema with the same $id already exists.
Schema with the same $id already present!
The JSON schema provided for validation to a route is not valid.
The JSON schema provided for serialization of a route response is not valid.
HTTP2 is available only from node >= 8.8.1.
Invalid initialization options.
Cannot set forceCloseConnections to idle as your HTTP server
does not support closeIdleConnections method.
The HTTP method already has a registered controller for that URL
The router received an invalid url.
The router received an error when using asynchronous constraints.
The defaultRoute type should be a function.
URL must be a string.
Fastify has already been closed and cannot be reopened.
Fastify is already listening.
Installed Fastify plugin mismatched expected version.
Callback for a hook is not a function (mapped directly from avvio)
Plugin must be a function or a promise.
Root plugin has already booted (mapped directly from avvio)
Impossible to load plugin because the parent (mapped directly from avvio)
Plugin did not start in time. Default timeout (in millis): 10000