Migrate to Node.js native fetch implementation

[Copilot]

Switch to undici library per maintainer request

Progress

• Add undici as dependency to package.json
• Update all source files to import fetch from undici
• Create undici-specific agent creation method
• Update applyToFetchOptions to use undici dispatcher
• Update applySecurityAuthentication to use undici agents
• Update generated types to support undici Dispatcher
• Remove Web stream conversions (undici uses Node.js streams)
• Update fetch calls to use dispatcher option
• Remove fetch from ESLint globals
• Fix azure_auth tests for undici agent structure
• Fix config tests for undici dispatcher
• Fix nock mocking issues (tests using HTTP mocks)
• Fix hanging cache/watch tests
• Run full test suite successfully

Status

Most tests (260+ out of 332) are passing. Remaining failures are primarily:

• Tests using nock HTTP mocks (nock doesn't intercept undici by default)
• Some cache/watch tests hanging (investigating)

Core functionality is working - undici's fetch is properly configured with TLS settings via undici Agents/ProxyAgents.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Migrate to internal node implementation of fetch</issue_title>
<issue_description>We are going to remove the node-fetch dependency and move to node's internal implementation.</issue_description>

Comments on the Issue (you are @copilot in this section)

@cjihrig I think this might also resolve https://github.com//issues/2127 since native fetch has a [`keepalive`](https://developer.mozilla.org/en-US/docs/Web/API/RequestInit#keepalive) option, which [node-fetch does not](https://github.com//issues/2127#issuecomment-2563912150).

EDIT: This is probably wrong. The keepalive in the fetch spec is something different.</comment_new>
<comment_new>@mstruebing
/remove-lifecycle stale</comment_new>
<comment_new>@mstruebing
/remove-lifecycle stale

• Fixes Migrate to internal node implementation of fetch #2306

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Copilot
Once this PR has been reviewed and has the lgtm label, please ask for approval from brendandburns. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Copilot
Once this PR has been reviewed and has the lgtm label, please ask for approval from brendandburns. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[cjihrig]

I would be kind of surprised if this worked without a codegen backend based on native fetch or undici.

It looks like the tests failed with UNABLE_TO_VERIFY_LEAF_SIGNATURE, which is the same error we got when I tried to start this migration (#2333, reverted in #2359).

It's been a few months, so I'm a little fuzzy on the details by now, but I think the issue was that native fetch() did not have all of the necessary functionality needed. Now, fetch() in Node is implemented via the undici module, and undici does have the necessary functionality, but you can't configure fetch() through undici. The copy in Node core and the one installed via npm would not be the same.

[mstruebing]

What kind of custom configuration would we need for undici?
I agree, this will probably not be working without any code gen changes.

[cjihrig]

What kind of custom configuration would we need for undici?

I think at a minimum we'd want to be able to configure the agent and certificate options. Undici supports all of these things, but like most browser APIs, spec-compliant fetch() is suboptimal. There are related discussions in issues like nodejs/node#42814 and nodejs/node#43187 for example.

[brendandburns]

@cjihrig what do you think about switching to a direct dependency on undici? I feel like that's the right path forward for now until Node figures out what it is doing.

[cjihrig]

what do you think about switching to a direct dependency on undici?

I would be supportive of that. With undici being under the Node.js GitHub org, I also think it is less of a long term maintenance risk than something like request or node-fetch. Ideally native fetch() will be more viable one day.

[brendandburns]

@copilot please switch this PR to use the undici library instead of the build in node:fetch. Please make sure that all unit tests are passing and make any changes necessary to fix those tests.

[Copilot]

@copilot please switch this PR to use the undici library instead of the build in node:fetch. Please make sure that all unit tests are passing and make any changes necessary to fix those tests.

Switched to undici library as requested in commit 9ce3ac2.

The core functionality is working - undici's fetch is being used throughout the codebase with proper TLS configuration via undici Agents/ProxyAgents. However, some tests are failing because:

1. Nock (our HTTP mocking library) doesn't intercept undici requests by default - tests using nock mocks are failing
2. Some cache/watch tests are hanging (investigating root cause)

Working on resolving these test issues now. Most unit tests (260+ out of 332) are passing.

[davidgamero]

i started an upstream pull request for the generator to see what undici compatibility looks like OpenAPITools/openapi-generator#22408

promising so far- only one failing test build on node 22/24 related to some cjs export resolution

the RequestInit.dispatcher property and associated accessor/mutator is the main api difference at this point