From 0d3ccd75cd7aadfcfdf1e3fa2d143463841fde3e Mon Sep 17 00:00:00 2001
From: Kaushal Kapasi <kaushal.kapasi@taplytics.com>
Date: Fri, 14 Mar 2025 15:45:40 -0400
Subject: [PATCH] feat: adds `RequireFlagsEnabled` decorator to allow reusable
 controller & endpoint access based on boolean flag values

Signed-off-by: Kaushal Kapasi <kaushal.kapasi@taplytics.com>
---
 packages/nest/src/index.ts                    |  1 +
 .../src/require-flags-enabled.decorator.ts    | 87 +++++++++++++++++++
 2 files changed, 88 insertions(+)
 create mode 100644 packages/nest/src/require-flags-enabled.decorator.ts

diff --git a/packages/nest/src/index.ts b/packages/nest/src/index.ts
index 20514df86..7296307e8 100644
--- a/packages/nest/src/index.ts
+++ b/packages/nest/src/index.ts
@@ -2,5 +2,6 @@ export * from './open-feature.module';
 export * from './feature.decorator';
 export * from './evaluation-context-interceptor';
 export * from './context-factory';
+export * from './require-flags-enabled.decorator';
 // re-export the server-sdk so consumers can access that API from the nestjs-sdk
 export * from '@openfeature/server-sdk';
diff --git a/packages/nest/src/require-flags-enabled.decorator.ts b/packages/nest/src/require-flags-enabled.decorator.ts
new file mode 100644
index 000000000..525cc563f
--- /dev/null
+++ b/packages/nest/src/require-flags-enabled.decorator.ts
@@ -0,0 +1,87 @@
+import {
+  applyDecorators,
+  CallHandler,
+  ExecutionContext,
+  HttpException,
+  mixin,
+  NestInterceptor,
+  NotFoundException,
+  UseInterceptors,
+} from '@nestjs/common';
+import { OpenFeature } from '@openfeature/server-sdk';
+
+/**
+ * Options for injecting a feature flag into a route handler.
+ */
+interface RequireFlagsEnabledProps {
+  /**
+   * The key of the feature flag.
+   * @see {@link Client#getBooleanValue}
+   */
+  flagKeys: string[];
+  /**
+   * The exception to throw if any of the required feature flags are not enabled.
+   * Defaults to a 404 Not Found exception.
+   * @see {@link HttpException}
+   */
+  exception?: HttpException;
+
+  /**
+   * The domain of the OpenFeature client, if a domain scoped client should be used.
+   * @see {@link OpenFeature#getClient}
+   */
+  domain?: string;
+}
+
+/**
+ * Returns a domain scoped or the default OpenFeature client with the given context.
+ * @param {string} domain The domain of the OpenFeature client.
+ * @returns {Client} The OpenFeature client.
+ */
+function getClientForEvaluation(domain?: string) {
+  return domain ? OpenFeature.getClient(domain) : OpenFeature.getClient();
+}
+
+/**
+ * Controller or Route permissions handler decorator.
+ *
+ * Requires that the given feature flags are enabled for the request to be processed, else throws an exception.
+ *
+ * For example:
+ * ```typescript
+ * @RequireFlagsEnabled({
+ *   flagKeys: ['flagName', 'flagName2'],  // Required, an array of Boolean feature flag keys
+ *   exception: new ForbiddenException(),  // Optional, defaults to a 404 Not Found exception
+ *   domain: 'my-domain',                  // Optional, defaults to the default OpenFeature client
+ * })
+ * @Get('/')
+ * public async handleGetRequest()
+ * ```
+ * @param {RequireFlagsEnabledProps} options The options for injecting the feature flag.
+ * @returns {Decorator}
+ */
+export const RequireFlagsEnabled = (props: RequireFlagsEnabledProps): ClassDecorator & MethodDecorator =>
+  applyDecorators(UseInterceptors(FlagsEnabledInterceptor(props)));
+
+const FlagsEnabledInterceptor = (props: RequireFlagsEnabledProps) => {
+  class FlagsEnabledInterceptor implements NestInterceptor {
+    constructor() {}
+
+    async intercept(context: ExecutionContext, next: CallHandler) {
+      const req = context.switchToHttp().getRequest();
+      const client = getClientForEvaluation(props.domain);
+
+      for (const flagKey of props.flagKeys) {
+        const endpointAccessible = await client.getBooleanValue(flagKey, false);
+
+        if (!endpointAccessible) {
+          throw props.exception || new NotFoundException(`Cannot ${req.method} ${req.url}`);
+        }
+      }
+
+      return next.handle();
+    }
+  }
+
+  return mixin(FlagsEnabledInterceptor);
+};