From 014e9a11f50b1fb0e03c3b9a4583701c5b2af18f Mon Sep 17 00:00:00 2001
From: Aral Balkan <mail@ar.al>
Date: Fri, 24 Jan 2020 20:37:55 +0000
Subject: [PATCH 1/2] Do not carry out proxy-related web output if the response
 is 404

---
 lib/http-proxy/passes/web-incoming.js | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/http-proxy/passes/web-incoming.js b/lib/http-proxy/passes/web-incoming.js
index 781b32692..ad13d689a 100644
--- a/lib/http-proxy/passes/web-incoming.js
+++ b/lib/http-proxy/passes/web-incoming.js
@@ -170,7 +170,7 @@ module.exports = {
     proxyReq.on('response', function(proxyRes) {
       if(server) { server.emit('proxyRes', proxyRes, req, res); }
 
-      if(!res.headersSent && !options.selfHandleResponse) {
+      if(!res.headersSent && !options.selfHandleResponse && (proxyRes.statusCode !== 404)) {
         for(var i=0; i < web_o.length; i++) {
           if(web_o[i](req, res, proxyRes, options)) { break; }
         }
@@ -182,7 +182,9 @@ module.exports = {
           if (server) server.emit('end', req, res, proxyRes);
         });
         // We pipe to the response unless its expected to be handled by the user
-        if (!options.selfHandleResponse) proxyRes.pipe(res);
+        if (!options.selfHandleResponse && (proxyRes.statusCode !== 404)) {
+          proxyRes.pipe(res);
+        }
       } else {
         if (server) server.emit('end', req, res, proxyRes);
       }

From 435806c127c3141c752bc287eed31d8d9ae6c6a6 Mon Sep 17 00:00:00 2001
From: Aral Balkan <mail@ar.al>
Date: Sun, 26 Jan 2020 23:15:02 +0000
Subject: [PATCH 2/2] Skip entire default proxyRes behaviour if fallthrough is
 requested

---
 lib/http-proxy/passes/web-incoming.js | 28 ++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/lib/http-proxy/passes/web-incoming.js b/lib/http-proxy/passes/web-incoming.js
index ad13d689a..8c4caabd4 100644
--- a/lib/http-proxy/passes/web-incoming.js
+++ b/lib/http-proxy/passes/web-incoming.js
@@ -170,23 +170,25 @@ module.exports = {
     proxyReq.on('response', function(proxyRes) {
       if(server) { server.emit('proxyRes', proxyRes, req, res); }
 
-      if(!res.headersSent && !options.selfHandleResponse && (proxyRes.statusCode !== 404)) {
-        for(var i=0; i < web_o.length; i++) {
-          if(web_o[i](req, res, proxyRes, options)) { break; }
+      if (!(options.fallthrough === true && proxyRes.statusCode === 404)) {
+        if(!res.headersSent && !options.selfHandleResponse) {
+          for(var i=0; i < web_o.length; i++) {
+            if(web_o[i](req, res, proxyRes, options)) { break; }
+          }
         }
-      }
 
-      if (!res.finished) {
-        // Allow us to listen when the proxy has completed
-        proxyRes.on('end', function () {
+        if (!res.finished) {
+          // Allow us to listen when the proxy has completed
+          proxyRes.on('end', function () {
+            if (server) server.emit('end', req, res, proxyRes);
+          });
+          // We pipe to the response unless its expected to be handled by the user
+          if (!options.selfHandleResponse) {
+            proxyRes.pipe(res);
+          }
+        } else {
           if (server) server.emit('end', req, res, proxyRes);
-        });
-        // We pipe to the response unless its expected to be handled by the user
-        if (!options.selfHandleResponse && (proxyRes.statusCode !== 404)) {
-          proxyRes.pipe(res);
         }
-      } else {
-        if (server) server.emit('end', req, res, proxyRes);
       }
     });
   }