This schema shows the internal lifecycle of Fastify.
The right branch of each section shows the next phase of the lifecycle. The left branch shows the corresponding error code generated if the parent throws an error. All errors are automatically handled by Fastify.
Incoming Request
│
└─▶ Routing
│
└─▶ Instance Logger
│
4**/5** ◀─┴─▶ onRequest Hook
│
4**/5** ◀─┴─▶ preParsing Hook
│
4**/5** ◀─┴─▶ Parsing
│
4**/5** ◀─┴─▶ preValidation Hook
│
400 ◀─┴─▶ Validation
│
4**/5** ◀─┴─▶ preHandler Hook
│
4**/5** ◀─┴─▶ User Handler
│
└─▶ Reply
│
4**/5** ◀─┴─▶ preSerialization Hook
│
└─▶ onSend Hook
│
4**/5** ◀─┴─▶ Outgoing Response
│
└─▶ onResponse Hook
Before or during the User Handler, reply.hijack() can be called to:
- Prevent Fastify from running subsequent hooks and the user handler
- Prevent Fastify from sending the response automatically
If reply.raw is used to send a response, onResponse hooks will still
be executed.
When the user handles the request, the result may be:
- In an async handler: it returns a payload or throws an
Error - In a sync handler: it sends a payload or an
Errorinstance
If the reply was hijacked, all subsequent steps are skipped. Otherwise, when submitted, the data flow is as follows:
★ schema validation Error
│
└─▶ schemaErrorFormatter
│
reply sent ◀── JSON ─┴─ Error instance
│
│ ★ throw an Error
★ send or return │ │
│ │ │
│ ▼ │
reply sent ◀── JSON ─┴─ Error instance ──▶ setErrorHandler ◀─────┘
│
reply sent ◀── JSON ─┴─ Error instance ──▶ onError Hook
│
└─▶ reply sent
reply sent means the JSON payload will be serialized by one of the following:
- The reply serializer if set
- The serializer compiler if a JSON schema is set for the HTTP status code
- The default
JSON.stringifyfunction