feat(proxy): implement express style middleware

Author: nkaradzhov

packages/test-utils/lib/index.ts

@@ -313,11 +313,10 @@ export default class TestUtils {
         //@ts-ignore
         targetPort: socketOptions.port,
         //@ts-ignore
-        targetHost: socketOptions.host,
+        targetHost: socketOptions.host ?? '127.0.0.1',
         enableLogging: true
       });
 
-
       await proxy.start();
       const proxyClient = client.duplicate({
         socket: {

packages/test-utils/lib/redis-proxy-spec.ts

@@ -1,7 +1,7 @@
 import { strict as assert } from 'node:assert';
 import { Buffer } from 'node:buffer';
 import { testUtils, GLOBAL } from './test-utils';
-import { RedisProxy } from './redis-proxy';
+import { InterceptorFunction, RedisProxy } from './redis-proxy';
 import type { RedisClientType } from '@redis/client/lib/client/index.js';
 
 describe('RedisSocketProxy', function () {
@@ -107,5 +107,61 @@ describe('RedisSocketProxy', function () {
       const pingResult = await proxiedClient.ping();
       assert.equal(pingResult, 'PONG', 'Client should be able to communicate with Redis through the proxy');
 
-    }, GLOBAL.SERVERS.OPEN_RESP_3)
+    }, GLOBAL.SERVERS.OPEN_RESP_3);
+
+  describe("Middleware", () => {
+    testUtils.testWithProxiedClient(
+      "Modify request/response via middleware",
+      async (
+        proxiedClient: RedisClientType<any, any, any, any, any>,
+        proxy: RedisProxy,
+      ) => {
+
+        // Intercept PING commands and modify the response
+        const pingInterceptor: InterceptorFunction = async (data, next) => {
+          if (data.includes('PING')) {
+            return Buffer.from("+PINGINTERCEPTED\r\n");
+          }
+          return next(data);
+        };
+
+        // Only intercept GET responses and double numeric values
+        // Does not modify other commands or non-numeric GET responses
+        const doubleNumberGetInterceptor: InterceptorFunction = async (data, next) => {
+          const response = await next(data);
+
+          // Not a GET command, return original response
+          if (!data.includes("GET")) return response;
+
+          const value = (response.toString().split("\r\n"))[1];
+          const number = Number(value);
+          // Not a number, return original response
+          if(isNaN(number)) return response;
+
+          const doubled = String(number * 2);
+          return Buffer.from(`$${doubled.length}\r\n${doubled}\r\n`);
+        };
+
+        proxy.setInterceptors([ pingInterceptor, doubleNumberGetInterceptor ])
+
+        const pingResponse = await proxiedClient.ping();
+        assert.equal(pingResponse, 'PINGINTERCEPTED', 'Response should be modified by middleware');
+
+        await proxiedClient.set('foo', 1);
+        const getResponse1 = await proxiedClient.get('foo');
+        assert.equal(getResponse1, '2', 'GET response should be doubled for numbers by middleware');
+
+        await proxiedClient.set('bar', 'Hi');
+        const getResponse2 = await proxiedClient.get('bar');
+        assert.equal(getResponse2, 'Hi', 'GET response should not be modified for strings by middleware');
+
+        await proxiedClient.hSet('baz', 'foo', 'dictvalue');
+        const hgetResponse = await proxiedClient.hGet('baz', 'foo');
+        assert.equal(hgetResponse, 'dictvalue', 'HGET response should not be modified by middleware');
+
+      },
+      GLOBAL.SERVERS.OPEN_RESP_3,
+    );
+  });
+
 });

packages/test-utils/lib/redis-proxy.ts

@@ -20,6 +20,7 @@ interface ConnectionInfo {
 interface ActiveConnection extends ConnectionInfo {
   readonly clientSocket: net.Socket;
   readonly serverSocket: net.Socket;
+  inflightRequestsCount: number
 }
 
 type SendResult =
@@ -49,11 +50,16 @@ interface ProxyEvents {
   'close': () => void;
 }
 
+export type Interceptor = (data: Buffer) => Promise<Buffer>;
+export type InterceptorFunction = (data: Buffer, next: Interceptor) => Promise<Buffer>;
+type InterceptorInitializer = (init: Interceptor) => Interceptor;
+
 export class RedisProxy extends EventEmitter {
   private readonly server: net.Server;
   public readonly config: Required<ProxyConfig>;
   private readonly connections: Map<string, ActiveConnection>;
   private isRunning: boolean;
+  private interceptorInitializer?: InterceptorInitializer;
 
   constructor(config: ProxyConfig) {
     super();
@@ -113,6 +119,13 @@ export class RedisProxy extends EventEmitter {
     });
   }
 
+  public setInterceptors(interceptors: Array<InterceptorFunction>) {
+    this.interceptorInitializer = (init) => interceptors.reduceRight<Interceptor>(
+      (next, mw) => (data) => mw(data, next),
+      init
+    );
+  }
+
   public getStats(): ProxyStats {
     const connections = Array.from(this.connections.values());
 
@@ -218,19 +231,22 @@ export class RedisProxy extends EventEmitter {
   }
 
   private handleClientConnection(clientSocket: net.Socket): void {
-    const connectionId = this.generateConnectionId();
+    clientSocket.pause();
     const serverSocket = net.createConnection({
       host: this.config.targetHost,
       port: this.config.targetPort
     });
+    serverSocket.once('connect', clientSocket.resume.bind(clientSocket));
 
+    const connectionId = this.generateConnectionId();
     const connectionInfo: ActiveConnection = {
       id: connectionId,
       clientAddress: clientSocket.remoteAddress || 'unknown',
       clientPort: clientSocket.remotePort || 0,
       connectedAt: new Date(),
       clientSocket,
-      serverSocket
+      serverSocket,
+      inflightRequestsCount: 0
     };
 
     this.connections.set(connectionId, connectionInfo);
@@ -243,12 +259,38 @@ export class RedisProxy extends EventEmitter {
       this.emit('connection', connectionInfo);
     });
 
-    clientSocket.on('data', (data) => {
+    clientSocket.on('data', async (data) => {
       this.emit('data', connectionId, 'client->server', data);
-      serverSocket.write(data);
+
+      if(!this.interceptorInitializer) {
+        serverSocket.write(data);
+        return;
+      }
+
+      connectionInfo.inflightRequestsCount++;
+
+      // next1 -> next2 -> ... -> last -> server
+      // next1 <- next2 <- ... <- last <- server
+      const last = (data: Buffer): Promise<Buffer> => {
+        return new Promise((resolve, reject) => {
+          serverSocket.write(data);
+          serverSocket.once('data', (data) => {
+            connectionInfo.inflightRequestsCount--;
+            assert(connectionInfo.inflightRequestsCount >= 0, `inflightRequestsCount for connection ${connectionId} went below zero`);
+            this.emit('data', connectionId, 'server->client', data);
+            resolve(data);
+          });
+          serverSocket.once('error', reject);
+        });
+      };
+
+      const interceptorChain = this.interceptorInitializer(last);
+      const response = await interceptorChain(data);
+      clientSocket.write(response);
     });
 
     serverSocket.on('data', (data) => {
+      if (connectionInfo.inflightRequestsCount > 0) return;
       this.emit('data', connectionId, 'server->client', data);
       clientSocket.write(data);
     });
@@ -273,6 +315,7 @@ export class RedisProxy extends EventEmitter {
     });
 
     serverSocket.on('error', (error) => {
+      if (connectionInfo.inflightRequestsCount > 0) return;
       this.log(`Server error for connection ${connectionId}: ${error.message}`);
       this.emit('error', error, connectionId);
       clientSocket.destroy();
@@ -306,6 +349,7 @@ export class RedisProxy extends EventEmitter {
   }
 }
 import { createServer } from 'net';
+import assert from 'node:assert';
 
 export function getFreePortNumber(): Promise<number> {
   return new Promise((resolve, reject) => {
@@ -326,4 +370,3 @@ export function getFreePortNumber(): Promise<number> {
 
 export { RedisProxy as RedisTransparentProxy };
 export type { ProxyConfig, ConnectionInfo, ProxyEvents, SendResult, DataDirection, ProxyStats };
-