feat(validation): Add Middy.js middleware for JSON Schema validation (#3694)

Co-authored-by: Andrea Amorosi <[email protected]>

Author: VatsalGoel3

Diff for: packages/validation/src/middleware.ts

@@ -0,0 +1,39 @@
+import { SchemaValidationError } from './errors.js';
+import type { ValidatorOptions } from './types.js';
+import { validate } from './validate.js';
+
+export function validation(options: ValidatorOptions) {
+  return {
+    before: async (handler: { event: unknown }) => {
+      if (options.inboundSchema) {
+        try {
+          handler.event = validate({
+            payload: handler.event,
+            schema: options.inboundSchema,
+            envelope: options.envelope,
+            formats: options.formats,
+            externalRefs: options.externalRefs,
+            ajv: options.ajv,
+          });
+        } catch (error) {
+          throw new SchemaValidationError('Inbound validation failed', error);
+        }
+      }
+    },
+    after: async (handler: { response: unknown }) => {
+      if (options.outboundSchema) {
+        try {
+          handler.response = validate({
+            payload: handler.response,
+            schema: options.outboundSchema,
+            formats: options.formats,
+            externalRefs: options.externalRefs,
+            ajv: options.ajv,
+          });
+        } catch (error) {
+          throw new SchemaValidationError('Outbound validation failed', error);
+        }
+      }
+    },
+  };
+}

Diff for: packages/validation/tests/unit/middleware.test.ts

@@ -0,0 +1,73 @@
+import middy from '@middy/core';
+import { describe, expect, it } from 'vitest';
+import { SchemaValidationError } from '../../src/errors.js';
+import { validation } from '../../src/middleware.js';
+
+const inboundSchema = {
+  type: 'object',
+  properties: {
+    inputValue: { type: 'number' },
+  },
+  required: ['inputValue'],
+  additionalProperties: false,
+};
+
+const outboundSchema = {
+  type: 'object',
+  properties: {
+    outputValue: { type: 'number' },
+  },
+  required: ['outputValue'],
+  additionalProperties: false,
+};
+
+const response = { outputValue: 20 };
+const baseHandler = async (event: unknown) => {
+  return response;
+};
+
+describe('validation middleware with Middy', () => {
+  it('should validate inbound and outbound successfully', async () => {
+    // Prepare
+    const middleware = validation({ inboundSchema, outboundSchema });
+    const wrappedHandler = middy(baseHandler).use(middleware);
+    const event = { inputValue: 10 };
+    // Act
+    const result = await wrappedHandler(event);
+    // Assess
+    expect(result).toEqual(response);
+  });
+
+  it('should throw error on inbound validation failure', async () => {
+    // Prepare
+    const middleware = validation({ inboundSchema });
+    const wrappedHandler = middy(baseHandler).use(middleware);
+    const invalidEvent = { inputValue: 'invalid' };
+    // Act & Assess
+    await expect(wrappedHandler(invalidEvent)).rejects.toThrow(
+      SchemaValidationError
+    );
+  });
+
+  it('should throw error on outbound validation failure', async () => {
+    const invalidHandler = async (_event: unknown) => {
+      return { outputValue: 'invalid' };
+    };
+    const middleware = validation({ outboundSchema });
+    const wrappedHandler = middy(invalidHandler).use(middleware);
+    const event = { any: 'value' };
+    // Act & Assess
+    await expect(wrappedHandler(event)).rejects.toThrow(SchemaValidationError);
+  });
+
+  it('should no-op when no schemas are provided', async () => {
+    // Prepare
+    const middleware = validation({});
+    const wrappedHandler = middy(baseHandler).use(middleware);
+    const event = { anyKey: 'anyValue' };
+    // Act
+    const result = await wrappedHandler(event);
+    // Assess
+    expect(result).toEqual(response);
+  });
+});