WIP: option to fall through to middleware chain on source 404 (#248)

README.md

@@ -225,6 +225,9 @@ Providing an alternative way to decide which requests should be proxied; In case
   }
   ```
 
+- **option.fallthrough**: boolean, sets whether execution should fall through to middleware chain when a 404 is encountered at the proxy target. If set, calls `next()` on the middleware chain.
+Default: `false`
+
 - **option.logLevel**: string, ['debug', 'info', 'warn', 'error', 'silent']. Default: `'info'`
 
 - **option.logProvider**: function, modify or replace log provider. Default: `console`.

package.json

@@ -51,7 +51,7 @@
     "@commitlint/cli": "^8.0.0",
     "@commitlint/config-conventional": "^8.0.0",
     "@types/express": "^4.17.0",
-    "@types/http-proxy": "^1.17.0",
+    "@types/http-proxy": "^1.17.3",
     "@types/is-glob": "^4.0.0",
     "@types/jest": "^24.0.15",
     "@types/lodash": "^4.14.136",
@@ -72,7 +72,7 @@
     "ws": "^7.1.0"
   },
   "dependencies": {
-    "http-proxy": "^1.17.0",
+    "http-proxy": "../node-http-proxy/",
     "is-glob": "^4.0.1",
     "lodash": "^4.17.14",
     "micromatch": "^4.0.2"

src/http-proxy-middleware.ts

@@ -19,8 +19,13 @@ export class HttpProxyMiddleware {
     this.config = createConfig(context, opts);
     this.proxyOptions = this.config.options;
 
+    let httpProxyOptions = <any>{}
+    if (context.fallthrough) {
+      httpProxyOptions.fallthrough = true
+    }
+
     // create proxy
-    this.proxy = httpProxy.createProxyServer({});
+    this.proxy = httpProxy.createProxyServer(httpProxyOptions);
     this.logger.info(
       `[HPM] Proxy created: ${this.config.context}  -> ${this.proxyOptions.target}`
     );
@@ -48,6 +53,18 @@ export class HttpProxyMiddleware {
   public middleware = async (req, res, next) => {
     if (this.shouldProxy(this.config.context, req)) {
       const activeProxyOptions = await this.prepareProxyRequest(req);
+
+      // fallthrough to the middleware chain if a resource
+      // cannot be found in the source being proxied
+      if (this.proxyOptions.fallthrough) {
+        this.proxy.once('proxyRes', (proxyRes) => {
+          if (proxyRes.statusCode === 404) {
+            this.logger.info('[HPM] Falling through to middleware chain on 404');
+            next();
+          }
+        });
+      }
+
       this.proxy.web(req, res, activeProxyOptions);
     } else {
       next();

test/e2e/_utils.ts

@@ -16,3 +16,16 @@ export function createServer(portNumber, middleware, path?) {
 
   return server;
 }
+
+export function createServerWithFallthrough(portNumber, middleware) {
+  const app = express();
+
+  app.use(middleware);
+  app.use((request, response, next) => {
+    response.end('fell through');
+  })
+
+  const server = app.listen(portNumber);
+
+  return server;
+}

test/e2e/http-proxy-middleware.spec.ts

@@ -1,5 +1,5 @@
 import * as http from 'http';
-import { createServer, proxyMiddleware } from './_utils';
+import { createServer, proxyMiddleware, createServerWithFallthrough } from './_utils';
 
 describe('E2E http-proxy-middleware', () => {
   describe('http-proxy-middleware creation', () => {
@@ -658,5 +658,90 @@ describe('E2E http-proxy-middleware', () => {
         expect(logMessage).not.toBeUndefined();
       });
     });
+
+    describe('404 fallthrough when requested', () => {
+      let proxyServer;
+      let targetServer;
+      let response;
+      let responseBody;
+
+      beforeEach(() => {
+        const mwProxy = proxyMiddleware('/', {
+          target: 'http://localhost:8000',
+          fallthrough: true
+        });
+
+        const mwTarget = (req, res, next) => {
+          // return 404 error
+          res.statusCode = 404;
+          res.end();
+        };
+
+        proxyServer = createServerWithFallthrough(3000, mwProxy);
+        targetServer = createServer(8000, mwTarget);
+      });
+
+      beforeEach(done => {
+        http.get('http://localhost:3000/', res => {
+          response = res;
+          res.on('data', chunk => {
+            responseBody = chunk.toString();
+            done();
+          });
+        });
+      });
+
+      afterEach(() => {
+        proxyServer.close();
+        targetServer.close();
+      });
+
+      it('should fall through', () => {
+        expect(response.statusCode).toBe(200);
+        expect(responseBody).toBe('fell through');
+      });
+    });
+
+    describe('404 do not fallthrough when not requested', () => {
+      let proxyServer;
+      let targetServer;
+      let response;
+      let responseBody;
+
+      beforeEach(() => {
+        const mwProxy = proxyMiddleware('/', {
+          target: 'http://localhost:8000',
+        });
+
+        const mwTarget = (req, res, next) => {
+          // return 404 error
+          res.statusCode = 404;
+          res.end('404 error');
+        };
+
+        proxyServer = createServerWithFallthrough(3000, mwProxy);
+        targetServer = createServer(8000, mwTarget);
+      });
+
+      beforeEach(done => {
+        http.get('http://localhost:3000/', res => {
+          response = res;
+          res.on('data', chunk => {
+            responseBody = chunk.toString();
+            done();
+          });
+        });
+      });
+
+      afterEach(() => {
+        proxyServer.close();
+        targetServer.close();
+      });
+
+      it('should not fall through', () => {
+        expect(response.statusCode).toBe(404);
+        expect(responseBody).toBe('404 error');
+      });
+    });
   });
 });

yarn.lock

@@ -494,10 +494,10 @@
     "@types/express-serve-static-core" "*"
     "@types/serve-static" "*"
 
-"@types/http-proxy@^1.17.0":
-  version "1.17.0"
-  resolved "https://registry.yarnpkg.com/@types/http-proxy/-/http-proxy-1.17.0.tgz#baf82ff6aa2723fd29f90e3ba1384e665006863e"
-  integrity sha512-l+s0IoxSHqhLFJPDHRfO235kgrCkvFD8JmdV/T9C4BKBYPIjrQopGFH4r7h2e3jQqgJRCthRCAZIxDoFnj1zwQ==
+"@types/http-proxy@^1.17.3":
+  version "1.17.3"
+  resolved "https://registry.yarnpkg.com/@types/http-proxy/-/http-proxy-1.17.3.tgz#348e1b808ff9585423cb909e9992d89ccdbf4c14"
+  integrity sha512-wIPqXANye5BbORbuh74exbwNzj+UWCwWyeEFJzUQ7Fq3W2NSAy+7x7nX1fgbEypr2/TdKqpeuxLnXWgzN533/Q==
   dependencies:
     "@types/node" "*"
 
@@ -1840,10 +1840,10 @@ eventemitter3@1.x.x:
   resolved "https://registry.yarnpkg.com/eventemitter3/-/eventemitter3-1.2.0.tgz#1c86991d816ad1e504750e73874224ecf3bec508"
   integrity sha1-HIaZHYFq0eUEdQ5zh0Ik7PO+xQg=
 
-eventemitter3@^3.0.0:
-  version "3.1.2"
-  resolved "https://registry.yarnpkg.com/eventemitter3/-/eventemitter3-3.1.2.tgz#2d3d48f9c346698fce83a85d7d664e98535df6e7"
-  integrity sha512-tvtQIeLVHjDkJYnzf2dgVMxfuSGJeM/7UCG17TT4EumTfNtF+0nebF/4zWOIkCreAbtNqhGEboB6BWrwqNaw4Q==
+eventemitter3@^4.0.0:
+  version "4.0.0"
+  resolved "https://registry.yarnpkg.com/eventemitter3/-/eventemitter3-4.0.0.tgz#d65176163887ee59f386d64c82610b696a4a74eb"
+  integrity sha512-qerSRB0p+UDEssxTtm6EDKcE7W4OaoisfIMl4CngyEhjpYglocpNg6UEqCvemdGhosAsg4sO2dXJOdyBifPGCg==
 
 exec-sh@^0.3.2:
   version "0.3.2"
@@ -2393,6 +2393,13 @@ http-errors@~1.6.2:
     setprototypeof "1.1.0"
     statuses ">= 1.4.0 < 2"
 
+http-proxy@../node-http-proxy/:
+  version "1.18.0"
+  dependencies:
+    eventemitter3 "^4.0.0"
+    follow-redirects "^1.0.0"
+    requires-port "^1.0.0"
+
 http-proxy@1.15.2:
   version "1.15.2"
   resolved "https://registry.yarnpkg.com/http-proxy/-/http-proxy-1.15.2.tgz#642fdcaffe52d3448d2bda3b0079e9409064da31"
@@ -2401,15 +2408,6 @@ http-proxy@1.15.2:
     eventemitter3 "1.x.x"
     requires-port "1.x.x"
 
-http-proxy@^1.17.0:
-  version "1.17.0"
-  resolved "https://registry.yarnpkg.com/http-proxy/-/http-proxy-1.17.0.tgz#7ad38494658f84605e2f6db4436df410f4e5be9a"
-  integrity sha512-Taqn+3nNvYRfJ3bGvKfBSRwy1v6eePlm3oc/aWVxZp57DQr5Eq3xhKJi7Z4hZpS8PC3H4qI+Yly5EmFacGuA/g==
-  dependencies:
-    eventemitter3 "^3.0.0"
-    follow-redirects "^1.0.0"
-    requires-port "^1.0.0"
-
 http-signature@~1.2.0:
   version "1.2.0"
   resolved "https://registry.yarnpkg.com/http-signature/-/http-signature-1.2.0.tgz#9aecd925114772f3d95b65a60abb8f7c18fbace1"