From d65ec54f23a17b98452e691b9263a59dfca5ec98 Mon Sep 17 00:00:00 2001
From: Nina Berg <nikb100@gmail.com>
Date: Mon, 7 Apr 2025 11:30:24 -0400
Subject: [PATCH] proxy-backend support sse connections closing

Signed-off-by: Nina Berg <nikb100@gmail.com>
---
 plugins/proxy-backend/src/service/router.ts | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/plugins/proxy-backend/src/service/router.ts b/plugins/proxy-backend/src/service/router.ts
index a6a52db63a..e58bccd7af 100644
--- a/plugins/proxy-backend/src/service/router.ts
+++ b/plugins/proxy-backend/src/service/router.ts
@@ -214,8 +214,12 @@ export function buildMiddleware(
     ].map(h => h.toLocaleLowerCase()),
   );
 
-  // only forward the allowed headers in backend->client
-  fullConfig.onProxyRes = (proxyRes: http.IncomingMessage) => {
+  fullConfig.onProxyRes = (
+    proxyRes: http.IncomingMessage,
+    _,
+    res: express.Response,
+  ) => {
+    // only forward the allowed headers in backend->client
     const headerNames = Object.keys(proxyRes.headers);
 
     headerNames.forEach(h => {
@@ -223,6 +227,14 @@ export function buildMiddleware(
         delete proxyRes.headers[h];
       }
     });
+
+    // handle SSE connections closed by the backend
+    // https://github.com/chimurai/http-proxy-middleware/discussions/765
+    proxyRes.on('close', () => {
+      if (!res.writableEnded) {
+        res.end();
+      }
+    });
   };
 
   if (reviveConsumedRequestBodies) {