Implement Labrinth Canary API flag (#5531)

packages/api-client/src/features/canary-cookie.ts

@@ -0,0 +1,37 @@
+import { AbstractFeature, type FeatureConfig } from '../core/abstract-feature'
+
+export const LABRINTH_CANARY_COOKIE = 'labrinth-canary=always'
+
+export interface CanaryCookieConfig extends FeatureConfig {
+	getCookie?: () => string | undefined | Promise<string | undefined>
+}
+
+export class CanaryCookieFeature extends AbstractFeature {
+	declare protected config: CanaryCookieConfig
+
+	constructor(config?: CanaryCookieConfig) {
+		super(config)
+	}
+
+	shouldApply(context: Parameters<AbstractFeature['shouldApply']>[0]): boolean {
+		return super.shouldApply(context) && context.options.api === 'labrinth'
+	}
+
+	async execute<T>(next: () => Promise<T>, context: Parameters<AbstractFeature['execute']>[1]) {
+		const cookie = this.config.getCookie ? await this.config.getCookie() : LABRINTH_CANARY_COOKIE
+		if (!cookie) {
+			return next()
+		}
+
+		const headers = { ...(context.options.headers ?? {}) }
+		const existingCookie = headers.cookie ?? headers.Cookie
+
+		if (!existingCookie?.split('; ').includes(cookie)) {
+			headers.cookie = existingCookie ? `${existingCookie}; ${cookie}` : cookie
+			delete headers.Cookie
+			context.options.headers = headers
+		}
+
+		return next()
+	}
+}