fix: avoid merging Set-Cookie headers in WrapHandler

Author: hexchain

lib/handler/wrap-handler.js

@@ -62,7 +62,13 @@ module.exports = class WrapHandler {
   onResponseStart (controller, statusCode, headers, statusMessage) {
     const rawHeaders = []
     for (const [key, val] of Object.entries(headers)) {
-      rawHeaders.push(Buffer.from(key), Array.isArray(val) ? val.map(v => Buffer.from(v)) : Buffer.from(val))
+      if (Array.isArray(val) && key === 'set-cookie') {
+        for (const v of val) {
+          rawHeaders.push(Buffer.from(key), Buffer.from(v))
+        }
+      } else {
+        rawHeaders.push(Buffer.from(key), Array.isArray(val) ? val.map(v => Buffer.from(v)) : Buffer.from(val))
+      }
     }
 
     if (this.#handler.onHeaders?.(statusCode, rawHeaders, () => controller.resume(), statusMessage) === false) {

test/issue-4389.js

@@ -0,0 +1,25 @@
+const { test } = require('node:test')
+const assert = require('node:assert')
+const { once } = require('node:events')
+const { createServer } = require('node:http')
+const { fetch, Agent } = require('..')
+
+test('Interceptor should not break Set-Cookie', async (t) => {
+  const server = createServer({ joinDuplicateHeaders: true }, async (_req, res) => {
+    const headers = [
+      ['set-cookie', 'a=1'],
+      ['set-cookie', 'b=2'],
+      ['set-cookie', 'c=3']
+    ]
+    res.writeHead(200, headers)
+    res.end()
+  }).listen(0)
+
+  await once(server, 'listening')
+  t.after(() => server.close())
+
+  const dispatcher = new Agent().compose((dispatch) => dispatch)
+
+  const { headers } = await fetch(`http://localhost:${server.address().port}`, { dispatcher })
+  assert.deepStrictEqual(headers.getSetCookie(), ['a=1', 'b=2', 'c=3'])
+})