Undici instrumentation interferes with custom dispatchers

[brkarcher]

Tracer Version(s)

5.63.0

Node.js Version(s)

22

Bug Report

Expected Behavior

When I call:

const dispatcher = new undici.Agent({
  connect: { keepAlive: false }
});

const response = await undici.fetch(url, {
  dispatcher,
});

Undici should create the underlying net library connection with keepAlive: false.

Actual Behavior

The dispatcher info is lost and the underlying net connection is not sent any keepAlive values.

Specifications

• Datadog Lambda Layer version: 84
• Node version: 22
• observed with dd-trace: 5.63.0.

Comments

NODE_DEBUG=net is useful here because it'll show us stuff like this:

NET 12: createConnection [
{
highWaterMark: 65536,
path: undefined,
localAddress: null,
port: '2773',
host: 'localhost'
},

keepAlive does show up there when specified.

My strong guess is that this is the code that's causing this bug. When we call in the style of undici.fetch(input: RequestInfo, init RequestInit) our input and info get repackaged into a globalThis.Request (being sent in here) which ends up dropping the dispatcher info.

This may be related to #6129 .

Reproduction Code

No response

Error Logs

No response

Tracer Config

No response

Operating System

No response

Bundling

Webpack