Some requests are slow for non-standard event-stream responses.

[zly2006]

Bug Description

A standard text/event-stream response has a space after the colon (event: ), but some server APIs do not implement it correctly, they dont have the space, and undici cannot resolve the fetch call until all response are sent back. This makes some AI & RAG chat very slow and user unfriendly.

Reproducible By

I am sorry this request requires some credentials, I am going to update a python or rust example server soon.

Expected Behavior

Resolve the fetch call after all headers are received. Do not wait for full response.

Logs & Screenshots

n/a

Environment

Node.js v25.2.1
MacOS 15.7.3

Additional context

I am trying to work on this issue, this is my first time trying to contribute to undici. I will maybe ask some dumb questions and try to submit a PR, thank you!

[mcollina]

Thanks for reporting!

Can you provide steps to reproduce? We often need a reproducible example, e.g. some code that allows someone else to recreate your problem by just copying and pasting it. If it involves more than a couple of different file, create a new repository on GitHub and add a link to that.

[zly2006]

Hi, after a few hours' attempt, I failed to reproduce this issue on my own. This issue happens on a private server and it needs api keys to access. Sharing that code on github is a bad idea, so, could you help me debug this? I can send you the code to reproduce with api key in private.

code with api keys removed:

const timeStart = Date.now();
fetch(
    `http://localhost:3002/api/proxy/api/v1/chat_query`,
    {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
        'Apikey': 'xx',
      },
      body: '{"Query":"你有什么功能？","UserID":"1","xx":"xx","ResponseMode":"streaming","AppKey":"xx"}',
    },
).then(() => {
  console.log('HTTP request completed at', Date.now() - timeStart, 'ms');
});

fetch(
    `https://xxxx/api/proxy/api/v1/chat_query`,
    {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
        'Apikey': 'xx',
      },
      body: '{"Query":"你有什么功能？","UserID":"1","AppConversationID":"xx","ResponseMode":"streaming","AppKey":"xx"}',
    },
).then(() => {
  console.log('HTTPS request completed at', Date.now() - timeStart, 'ms');
})

Log:

HTTP request completed at 292 ms
HTTPS request completed at 10655 ms

Nginx configurantion:

    server {
        listen       3002;
        location / {
            proxy_buffering off;
            
            proxy_pass https://xxx; # (the private server)
        }
    }

[metcoder95]

If this is not easily reproducible and requires a remote setup, is likely that the issue roots to the server configuration and not fetch/undici itself