Bug 304164 – REGRESSION (298981@main): fetch() throws TypeError when using targetAddressSpace: 'loopback' with localhost requests

• Component: DOM
• Status: RESOLVED FIXED

Description

When making a simple fetch() request to a locally deployed HTTP service (e.g. 127.0.0.1), Safari 26.2 throws a TypeError and immediately enters the catch block if the targetAddressSpace: 'loopback' option is provided.

This behavior does not occur in:

Safari 26.1

Chrome (where targetAddressSpace: 'loopback' is required for compatibility)

If any other arbitrary option is passed instead (e.g. { a: "abc" }), the request succeeds normally in Safari 26.2.

Steps to Reproduce

Start a simple local HTTP server:

Example: http://127.0.0.1:8080

Endpoint returns plain text via GET

Run the following code in Safari 26.2:

fetch('http://127.0.0.1:8080', {
  targetAddressSpace: 'loopback'
})
  .then(response => response.text())
  .then(text => console.log(text))
  .catch(error => console.error(error));

Expected Result

The request succeeds

Response text is logged to the console

Actual Result

The request immediately fails

catch is triggered with a TypeError

No network request is completed

[Radar WebKit Bug Importer]

<rdar://problem/166574523>

[Ryosuke Niwa]

This is because we don’t support “loopback” for IPAddressSpace:
https://wicg.github.io/local-network-access/#ip-address-space-section

[Ryosuke Niwa]

Pull request: https://github.com/WebKit/WebKit/pull/55516

[EWS]

Committed 304577@main (295fd224c10d): <https://commits.webkit.org/304577@main>

Reviewed commits have been landed. Closing PR #55516 and removing active labels.