http: respect Keep-Alive timeout hint when agent has no explicit timeout

[DivyanshuX9]

When an http.Agent is created with keepAlive: true but no explicit timeout option, the server's Keep-Alive: timeout=N response header is silently ignored. The socket is returned to the pool with socket.setTimeout(0), which disables the idle timer entirely. The server eventually closes the connection, but the socket remains in freeSockets. The next request that reuses it receives ECONNRESET.

Root cause

In keepSocketAlive(), agentTimeout is derived from the agent's timeout option:

let agentTimeout = this.options.timeout || 0;

When no timeout is configured, agentTimeout is 0. The branch that applies the server hint:

} else if (serverHintTimeout < agentTimeout) {

can never be true when agentTimeout === 0 (since serverHintTimeout is always positive after buffer subtraction). As a result, socket.setTimeout(0) is called, disabling the idle timer.

Fix

Also apply the server hint when agentTimeout === 0 (i.e., no client-side timeout is configured). The server's hint is the only available signal, so it should be respected rather than discarded.

Test

Four cases covering:

server hint only (no agent timeout) — socket timer set to hint

agent timeout shorter than hint — agent timeout wins

agent timeout longer than hint — hint wins

no hint, no agent timeout — timer stays disabled (socket.setTimeout(0))

Refs: #52649
Fixes: #66734

[nodejs-github-bot]

Review requested:

• @nodejs/http
• @nodejs/net

[Copilot]

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[DivyanshuX9]

This fixes #66734: an http.Agent with keepAlive: true and no timeout ignored the server’s Keep-Alive: timeout=N hint. It’s a one-line change in keepSocketAlive plus a regression test. It narrows but doesn’t fully close the race in #52649. Could a collaborator start CI and take a look when you have time?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.50%. Comparing base (1c90519) to head (4363a84).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #66737   +/-   ##
=======================================
  Coverage   90.49%   90.50%           
=======================================
  Files         797      797           
  Lines      277598   277598           
  Branches    53336    53339    +3     
=======================================
+ Hits       251220   251228    +8     
+ Misses      16790    16783    -7     
+ Partials     9588     9587    -1     

Files with missing lines	Coverage Δ
lib/internal/http/agent.js	97.06% <100.00%> (+0.41%)	⬆️

... and 28 files with indirect coverage changes

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