Socket event listeners are attached multiple times, causing a memory leak with keepAlive agents

[0xHristo]

Socket Event Listener Leak with keepAlive https.Agent

Issue Description

When using the plugin with a keepAlive https.Agent, socket event listeners are attached on every request.
Over time, this accumulates listeners on the same socket, which can trigger memory leaks and MaxListenersExceededWarnings.

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Expected Behavior

Each socket should only have one set of event listeners attached, regardless of how many requests reuse that socket.

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Actual Behavior

Event listeners are attached multiple times to the same socket.
The listener count grows with each request made through the plugin.

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Reproduction Steps

1. Use a keepAlive https.Agent.
2. Make repeated requests through the plugin.
3. Inspect the socket and check event listener counts.
4. Observe that listener counts grow beyond 1.

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Suggested Fix

Add a per-socket guard before attaching listeners, ensuring that each socket is instrumented only once:

if (!socket.haveEvents) {
  socket.haveEvents = true;
  // attach listeners
}

This prevents duplicate listener attachment when sockets are reused by the agent.

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Environment

• Node.js: all
• superagent: all
• OS: all

[0xHristo]

I’ve opened MR #22 to fix this issue.