fix: preserve DNS origin hostname on sockets

[cyphercodes]

This relates to...

Fixes #5573

Rationale

The DNS interceptor connects to a selected IP address, which causes Node's net.client.socket diagnostics channel to expose the IP as socket._host. Consumers can no longer correlate TCP connection timing with the original request hostname.

Changes

• pass the request hostname through HTTP connection setup
• connect to the interceptor-selected IP through a fixed lookup while preserving the logical hostname on the socket
• add regression coverage for socket._host and remoteAddress

Features

N/A

Bug Fixes

• preserve the original DNS hostname in HTTP socket diagnostics when the DNS interceptor selects an IP

Breaking Changes and Deprecations

N/A

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

Testing:

• node --test --test-name-pattern='#5573' test/interceptors/dns.js
• npm run test:interceptors
• npm run lint
• npm run test:typescript

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.48%. Comparing base (f36ea9c) to head (4de0540).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5577   +/-   ##
=======================================
  Coverage   93.47%   93.48%           
=======================================
  Files         110      110           
  Lines       37564    37610   +46     
=======================================
+ Hits        35114    35159   +45     
- Misses       2450     2451    +1     

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[cyphercodes]

Pushed a small test-only follow-up in 306602e to avoid relying on the net.client.socket diagnostics channel in the new DNS socket regression. The test now captures the socket/options through net.connect, which should avoid the Windows timeout while preserving the same assertions.

Verification run locally:

• node --test test/interceptors/dns.js
• npm run lint -- test/interceptors/dns.js
• git diff --check

[cyphercodes]

Pushed a Windows-focused test follow-up in 67808e2. The HTTP DNS regression no longer asserts socket.remoteAddress, which is empty on the Windows runner after the request completes; it now verifies the preserved hostname and the injected lookup result instead.

Verification run locally:

• node --test --test-name-pattern "#5573" test/interceptors/dns.js
• npm run lint -- test/interceptors/dns.js
• git diff --check

Note: a full local node --test test/interceptors/dns.js run hit the existing TLS/SNI local-environment failure in Should respect DNS origin hostname for SNI on TLS, while the targeted #5573 regression passed.

[mcollina]

what about https?

[cyphercodes]

Pushed a small follow-up in 4de0540 for the HTTPS review note. The client now stores request.servername before opening a new connection for all protocols; HTTPS keeps the existing SNI/change handling, while HTTP still passes the preserved hostname through the connector lookup path.

Verification run locally:

• node --test --test-name-pattern "#5573" test/interceptors/dns.js
• npm run lint -- test/interceptors/dns.js lib/dispatcher/client.js
• git diff --check

[mcollina]

lgtm

[jasnell]

The _hostname here could use a comment. At first glance, the _hostname here and the address: hostname below look like a typo/mistake. A comment indicating that the _hostname is intentionally being ignored is helpful.