fix(API): Return a request schema for decorator routes in /discover (backport to release-candidate/2.35.x) (#36497)

Co-authored-by: Uddish Verma <uddish.verma@n8n.io>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

packages/cli/src/public-api/v1/handlers/discover/__tests__/discover.service.test.ts

@@ -194,6 +194,19 @@ describe('buildDiscoverResponse', () => {
 		expect(createEndpoint?.requestSchema).toHaveProperty('type');
 	});
 
+	it('should include requestSchema for a decorator route when includeSchemas is true', async () => {
+		const result = await buildDiscoverResponse(['role:manage'] as ApiKeyScope[], {
+			includeSchemas: true,
+		});
+
+		const createEndpoint = result.resources.role?.endpoints.find(
+			(e) => e.operationId === 'createRole',
+		);
+		expect(createEndpoint).toBeDefined();
+		expect(createEndpoint?.requestSchema).toBeDefined();
+		expect(createEndpoint?.requestSchema).toHaveProperty('properties');
+	});
+
 	it('should not include requestSchema on GET endpoints even with includeSchemas', async () => {
 		const result = await buildDiscoverResponse(['tag:list'] as ApiKeyScope[], {
 			includeSchemas: true,

packages/cli/src/public-api/v1/handlers/discover/discover.service.ts

@@ -12,6 +12,7 @@ import {
 	scopesInRequirement,
 	toOpenApiPathTemplate,
 } from '../../../public-api-route-resolver';
+import { buildRequestBodyJsonSchema } from '../../openapi-gen/decorator-routes';
 import { extractScopeFromEovHandlerChain } from '../../shared/public-api-scope-lookup';
 
 import '../../controllers';
@@ -151,6 +152,7 @@ function buildDecoratorEndpoints(): EndpointInfo[] {
 		operationId: route.handlerName,
 		tag: route.tags?.[0] ?? 'Other',
 		scope: route.apiKeyScope ?? null,
+		requestSchema: buildRequestBodyJsonSchema(route),
 	}));
 }
 

packages/cli/src/public-api/v1/openapi-gen/__tests__/request-body-schema-parity.test.ts

@@ -0,0 +1,41 @@
+import fs from 'node:fs';
+import path from 'node:path';
+import { parse } from 'yaml';
+
+import { resolvePublicApiRoutes } from '@/public-api/public-api-route-resolver';
+
+import { buildRequestBodyJsonSchema, getDecoratorGeneratedOperations } from '../decorator-routes';
+
+/**
+ * The build writes a request body schema into the spec. `/discover` builds the same schema at
+ * runtime, through `buildRequestBodyJsonSchema`. Nothing else checks that the two agree.
+ */
+const V1_DIR = path.resolve(__dirname, '../..');
+
+// The build writes one spec file per route and names it after the handler method, so the handler
+// name is what links a route to its file.
+const SPEC_FILE_BY_HANDLER = new Map(
+	getDecoratorGeneratedOperations().map((operation) => [
+		operation.config.operationId,
+		operation.outputPath,
+	]),
+);
+
+function schemaInSpecFile(handlerName: string): unknown {
+	const specFile = SPEC_FILE_BY_HANDLER.get(handlerName);
+	if (!specFile) throw new Error(`The build generated no spec file for ${handlerName}`);
+
+	const spec = parse(fs.readFileSync(path.join(V1_DIR, specFile), 'utf8')) as {
+		requestBody?: { content?: Record<string, { schema?: unknown }> };
+	};
+
+	return spec.requestBody?.content?.['application/json']?.schema;
+}
+
+describe('buildRequestBodyJsonSchema', () => {
+	const routesWithBody = resolvePublicApiRoutes().filter((route) => route.requestBodyDto);
+
+	it.each(routesWithBody)('$handlerName matches its committed spec file', (route) => {
+		expect(buildRequestBodyJsonSchema(route)).toEqual(schemaInSpecFile(route.handlerName));
+	});
+});

packages/cli/src/public-api/v1/openapi-gen/decorator-routes.ts

@@ -5,8 +5,10 @@ import './zod-extend';
 // resolvePublicApiRoutes()
 import '../controllers';
 
+import { OpenAPIRegistry, OpenApiGeneratorV3 } from '@asteasolutions/zod-to-openapi';
 import type { RouteConfig } from '@asteasolutions/zod-to-openapi';
 import type { ResponseDtoClass } from '@n8n/decorators';
+import { isRecord } from '@n8n/utils/is-record';
 import { UnexpectedError } from 'n8n-workflow';
 import { z } from 'zod';
 
@@ -17,6 +19,8 @@ import {
 	toOpenApiPathTemplate,
 } from '@/public-api/public-api-route-resolver';
 
+const REQUEST_BODY_COMPONENT = 'RequestBody';
+
 // Query fields backed by shared hand-written parameter files instead of being generated
 const SHARED_PAGINATION_PARAMS: Record<string, { $ref: string }> = {
 	limit: { $ref: '../../../../shared/spec/parameters/limit.yml' },
@@ -137,6 +141,25 @@ function buildRequestBody(
 	};
 }
 
+/**
+ * Converts a route's `@Body` DTO into JSON Schema, using the same conversion the build runs when
+ * it writes the OpenAPI files. zod-to-openapi can only convert a schema that a registry holds, so
+ * this registers one under a throwaway name and then reads the result back out.
+ */
+export function buildRequestBodyJsonSchema(
+	route: ResolvedPublicApiRoute,
+): Record<string, unknown> | undefined {
+	if (!route.requestBodyDto) return undefined;
+
+	const registry = new OpenAPIRegistry();
+	registry.register(REQUEST_BODY_COMPONENT, route.requestBodyDto.schema);
+
+	const { components } = new OpenApiGeneratorV3(registry.definitions).generateComponents();
+	const schema = components?.schemas?.[REQUEST_BODY_COMPONENT];
+
+	return isRecord(schema) ? schema : undefined;
+}
+
 /**
  * Response set is derived from what `PublicApiControllerRegistry` actually does at runtime, not
  * invented: the success status is the one `@ApiResponse` declares (and the same one the registry