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Guard Middleware Decorator

The @Guard decorator registers a guard to control access to controllers or methods.

Purpose​

Guards are used to validate incoming requests before they reach route handlers. They act as gatekeepers that determine whether a request should be allowed to proceed. If any guard returns false, the request is blocked and further processing is stopped.

Usage​

Apply the @Guard decorator to a class or method, passing a guard class or function that implements the guard logic.

Parameters​

  • guard: Guard | GuardFn - A guard class or function used to determine whether the request is allowed to proceed.

Examples​

Function Guard​

@Guard((req, res) => {
  // Allow only if authorization header is present
  return !!req.headers.authorization;
})
class MyController {}

Class-based Guard​

class AuthGuard {
  canActivate(req: Request, res: Response) {
    // Allow only if authorization header is present
    return !!req.headers.authorization;
  }
}

@Guard(AuthGuard)
class MyController {}

Metadata Handling​

The decorator attaches the guard(s) as metadata on the target class or method using a specific metadata key (CONTROLLER_CONFIGUARTION). This metadata is accessible via the Reflect API and is used internally by the framework during request processing to enforce guard checks.

Remarks​

  • Guards are executed before controller methods.
  • They can be used for authentication, authorization, and request validation.
  • If any guard returns false, the request handling is stopped.
  • Multiple guards can be applied by using the decorator multiple times or passing an array (if supported).