Error occurred while processing headers when request http2

[binsee]

Bug Description

When requesting http2 continuously, an error will occur when the headers contain the Content-Type field and other headers.

When requesting http2, the first request will actually use Request[kHTTP1BuildRequest] instead of Request[kHTTP2BuildRequest], so this issue will not be triggered. Related:
#2326

Reproducible By

test code:

import { Pool, request } from 'undici'
import { setTimeout as sleep } from 'timers/promises'
import { createSecureServer } from 'http2'
import pem from 'https-pem'
import { AddressInfo } from 'net'

async function main() {
  const server = createSecureServer({ ...pem, allowHTTP1: false })
  server
    .on('request', (req, rsp) => {
      console.log('server receive request:', req.method, req.url.toString())
      rsp.setHeader('Content-Type', 'text/html; charset=utf-8')
      rsp.write('hello')
      rsp.end()
    })
    .listen(0)

  const host = `https://localhost:${(server.address() as AddressInfo).port}`
  const client = new Pool(host, {
    allowH2: true,
    connections: 1,
    connect: { rejectUnauthorized: false },
  })

  for (let i = 0; i < 5; i++) {
    console.log(`before request [${i}]`)
    const rsp = await request(`${host}/test`, {
      method: 'GET',
      dispatcher: client,
      headers: {
        'Content-Type': 'application/text',
        otherHeader: 'test',
      },
    })

    console.log('client receive response:', rsp.statusCode)
    console.log(`after request [${i}]\n`)
  }

  await sleep(5e3)
}

void main()

Expected Behavior

No error occurs

Logs & Screenshots

I added some logs in undici to track the behavior of the code

before request [0]
[undici] client[kDispatch] kHTTPConnVersion h1
[undici] request processHeader { key: 'Content-Type', val: 'application/text', skipAppend: false }
[undici] request processHeader { key: 'name', val: '111', skipAppend: false }
[undici] client.connect() socket.alpnProtocol h2 Error
    at connect (/Users/test/node_modules/undici/lib/client.js:1231:87)
(node:40259) [UNDICI-H2] Warning: H2 support is experimental, expect them to change at any time.
(Use `node --trace-warnings ...` to show where the warning was created)
server receive request: POST /test
client receive response: 200
after request [0]

before request [1]
[undici] client[kDispatch] kHTTPConnVersion h2
[undici] request processHeader { key: 'Content-Type', val: 'application/text', skipAppend: true }
[undici] request processHeader { key: 'name', val: '111', skipAppend: true }
/Users/test/node_modules/undici/lib/core/request.js:434
      if (skipAppend) request.headers[key] = processHeaderValue(key, val, skipAppend)
                                           ^
TypeError: Cannot create property 'name' on string '[object Object]Content-Type: application/text
'
    at processHeader (/Users/test/node_modules/undici/lib/core/request.js:434:44)
    at Function.[http2 build request] (/Users/test/node_modules/undici/lib/core/request.js:314:9)
    at Client.[dispatch] (/Users/test/node_modules/undici/lib/client.js:361:36)
    at Client.Intercept (/Users/test/node_modules/undici/lib/interceptor/redirectInterceptor.js:11:16)
    at Client.dispatch (/Users/test/node_modules/undici/lib/dispatcher-base.js:179:40)
    at Pool.[dispatch] (/Users/test/node_modules/undici/lib/pool-base.js:143:28)
    at Pool.dispatch (/Users/test/node_modules/undici/lib/dispatcher-base.js:179:40)
    at Pool.request (/Users/test/node_modules/undici/lib/api/api-request.js:169:10)
    at /Users/test/node_modules/undici/lib/api/api-request.js:162:15
    at new Promise (<anonymous>)

Environment

• MacOS 14.0
• Nodejs 16.19.0
• undici 5.25.4

Additional context