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

[DivyanshuX9]

Description

When an http.Agent is created with keepAlive: true but without an 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), disabling the idle timer entirely. The server eventually closes the idle connection, but the socket remains in freeSockets. Subsequent requests reusing the socket receive an 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 on the agent, agentTimeout is 0. The branch that applies the server hint:

} else if (serverHintTimeout < agentTimeout) {

can never evaluate to true when agentTimeout === 0 (since serverHintTimeout is positive after subtracting the buffer). As a result, socket.setTimeout(0) is invoked and the idle timer is disabled.

Fix

Apply the server hint when agentTimeout === 0 as well (agentTimeout === 0 || serverHintTimeout < agentTimeout). When no client-side timeout is specified, the server hint is the authoritative signal for connection lifetime and is applied to the socket timeout.

Tests

Added test/parallel/test-http-agent-keep-alive-server-hint.js covering four scenarios:

Server hint only (no agent timeout): Server hint applies to idle socket timer (hint - buffer).
Explicit agent timeout > server hint: Server hint wins.
Explicit agent timeout < server hint: Agent timeout wins.
No server hint, no agent timeout: Timer remains disabled (socket.setTimeout(0)), retaining original behavior.

Supersedes: #66737 Fixes: #66734
Refs: #52649

[nodejs-github-bot]

Review requested:

• @nodejs/http
• @nodejs/net

[Copilot]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.51%. Comparing base (1c90519) to head (a12dfcb).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66779      +/-   ##
==========================================
+ Coverage   90.49%   90.51%   +0.01%     
==========================================
  Files         797      797              
  Lines      277598   277598              
  Branches    53336    53345       +9     
==========================================
+ Hits       251220   251257      +37     
+ Misses      16790    16776      -14     
+ Partials     9588     9565      -23     

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

... and 29 files with indirect coverage changes

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