OnRequest

OnRequest is a term used in web application frameworks to describe an early lifecycle hook that runs when an HTTP request is received. It represents one of the initial points where server-side code can observe and influence the processing of a request, before routing, authentication, or business logic executes.

In many frameworks, onRequest handlers fire immediately after the server accepts a connection but before most subsequent processing. They are typically lightweight and stateless, serving purposes such as request logging, input normalization, basic security checks, rate limiting, and attaching metadata (for example, a correlation ID) to the request for use by downstream handlers.

A key aspect of onRequest is that a handler can terminate the normal processing chain by returning a response directly. Because this hook runs very early, it is encouraged to avoid heavy I/O or operations that depend on downstream components. Handlers may also mutate the request object to pass information to later stages, such as marking the request as authenticated or augmenting it with parsed data.

Variations exist across frameworks; the hook may be named onRequest or have a similar extension point with a different label (for example, beforeRequest, preRouting, or preHandler). The behavior and ordering of multiple onRequest handlers are framework-specific and typically configured by the developer.

Related concepts include middleware, which often operates later in the request lifecycle, and other lifecycle hooks such as preAuth or onResponse used to implement cross-cutting concerns at different stages of request processing.