Support Type-Safety Headers

[mikoloism]

Hi, is there a way to use type-safety in using headers or not?

If not, how can I help to develop and add this feature?

[mikoloism]

Hi again,

A solution that came to my mind is to extend the built-in Headers class in Deno and inject the types in the form of generic-type and put them in the ./headers.ts file...

Something like this:

const DenoHeaders = Headers;

class SafeHeaders<Keys extends ReadonlyArray<string>> extends DenoHeaders {
	public override get<K extends Keys[number]>(key: K) {
		return super.get(key);
	}

	public override set<K extends Keys[number]>(key: K, value: string) {
		return super.set(key, value);
	}
}

class SaferHeaders<Keys extends Record<string, unknown>> extends DenoHeaders {
	public override get<K extends keyof Keys>(key: K) {
		return super.get(<string>key);
	}

	public override set<V extends Keys[K], K extends keyof Keys>(key: K, value: string & V) {
		return super.set(<string>key, String(value));
	}
}

type MyCustomHeaders = {
	'x-usertype-key': 'admin' | 'normal' | 'guest';
	'x-another-key': string;
};

type MyCustomHeaderKeys = [keyof MyCustomHeaders];

const unsafe = new DenoHeaders();
const safe = new SafeHeaders<MyCustomHeaderKeys>();
const safer = new SaferHeaders<MyCustomHeaders>();

// -> no care to KEY passed and not suggest KEYS
unsafe.get('x-use');

// -> care to KEY passed and suggest KEYS (and VALUE if nedded)
safe.get('x-usertype-key');
safer.set('x-usertype-key', 'guest');

And well, for use outside the file, we can export as follows:

// headers.ts
export { ExtendedClass as Headers } 

// and import in other files
// then, where this "header" is used,
// the generic-type can be obtained from the top-level module/function/class and passed, if needed
/// or, using global declaration file, if needed

If I accept and need this features, I can do this and apply changes to all related files

NOTICE:
Here are two options to improve typing performance in the Headers class, SAFE and SAFER. Here we have the right to choose :)