fix(proxy): forward SSE close event (#13578)

Author: sapphi-red

packages/vite/src/node/server/middlewares/proxy.ts

@@ -91,6 +91,17 @@ export function proxyMiddleware(
       })
     })
 
+    // https://github.com/http-party/node-http-proxy/issues/1520#issue-877626125
+    // https://github.com/chimurai/http-proxy-middleware/blob/cd58f962aec22c925b7df5140502978da8f87d5f/src/plugins/default/debug-proxy-errors-plugin.ts#L25-L37
+    proxy.on('proxyRes', (proxyRes, req, res) => {
+      res.on('close', () => {
+        if (!res.writableEnded) {
+          debug?.('destroying proxyRes in proxyRes close event')
+          proxyRes.destroy()
+        }
+      })
+    })
+
     // clone before saving because http-proxy mutates the options
     proxies[context] = [proxy, { ...opts }]
   })