Allow passing a function to the @Header decorator for dynamic values

[mrVito]

Is there an existing issue that is already proposing this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe it

I'm trying to attach a 'Last-Modified' header on my API response and was initially trying to use this code:

@Header('Last-Modified', new Date().toUTCString())

Unfortunatelly this doesn't work as expected, as the value for the header is only evaluated once at startup and thus it is the same value on every request.

Describe the solution you'd like

Would be great if we could pass a function to the value argument of the @Header decorator that is evaluated on every request to the given endpoint so we can have dynamic values for the header.

Teachability, documentation, adoption, migration strategy

Use a function for the value argument on the @Header decorator to evaluate an expression on every request:

@Header('Last-Modified', () => new Date().toUTCString())

What is the motivation / use case for changing the behavior?

I have currently moved on to using an injected response object (using @Res decorator) and setting the header directly on it which is all fine, but it is not really nice to have additional native response handling code when only a simple header is needed and thus the nest.js way would be much more elegant.

[kamilmysliwiec]

Would you like to create a PR for this issue?

Simply about this method to check if value is function and if so, execute it:

nest/packages/core/router/router-response-controller.ts

Lines 82 to 89 in 22b7946

	public setHeaders<TResponse = unknown>(
	response: TResponse,
	headers: CustomHeader[],
	) {
	headers.forEach(({ name, value }) =>
	this.applicationRef.setHeader(response, name, value),
	);
	}

[kamilmysliwiec]

Let's track this here #13027