Скачать или смотреть Understanding Why Your Node.js Client HTTP Connections Might Not Close Properly

Explore the common reasons for lingering HTTP connections in Node.js servers and learn effective strategies for ensuring all connections are closed during testing.
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Troubleshooting Non-Closing HTTP Connections in Node.js

In the realm of server-side development, maintaining clean connections is crucial. Many developers running a Node.js server encounter an intriguing issue: HTTP connections that refuse to close. If you've run tests using frameworks like Mocha only to find lingering connections at the end, you're not alone. Let's explore why this happens and how you can address it effectively.

The Problem Defined

When running tests against your Node.js server, you may notice that upon shutting down, the server still reports active connections. In our case:

Environment: Node.js (12.18.4)

Frameworks: Mocha, Request

Symptoms: After testing, connections count remains at 60-70, even though no tests failed or became stuck.

The critical question arises: Why does the server believe these connections are still active?

Digging into the Root Cause

It’s tempting to pinpoint the failure on some aspects of your code or the testing framework, but let's consider a different perspective:

Transient Nature of Connections: TCP connections can be slow to close due to various factors, such as operating system behavior or network latency. Therefore, even if your application logic is complete, the OS might still be hanging on to these connections for brief periods.

Rethinking the Approach

Instead of obsessing over the count of active connections, we can adopt a more pragmatic approach. Here’s how:

1. Move Away from getConnections

Instead of asserting the number of active connections with server.getConnections, consider the following:

Evaluate the Necessity: While it seems important to know the exact count, the robustness of your tests may not rely on it. If every test completed successfully, why stress over connections that will eventually close?

2. Utilize server.close(cb)

Instead of checking connections, a better method is to directly call server.close(cb). Here’s how that works:

Immediate Response: If the server has no active connections, the close callback (cb) is triggered instantly.

Wait for Connections to Drain: If connections do exist, the callback waits for all of them to close before proceeding.

Setting Timeouts: Establish a test timeout to handle cases where connections stubbornly refuse to close down.

Streamlining Your Code Base

By focusing on server.close, you simplify the handling of server state during tests. Consider this flow in your testing setup:

[[See Video to Reveal this Text or Code Snippet]]

This way, you remove unnecessary complexity from connection management, leading to cleaner, more reliable tests.

Conclusion

While it’s essential to ensure connections are closed properly, the focus on exact counts can lead you down a rabbit hole. By leveraging the capabilities of the server.close(cb) method, you can handle your server connections more effectively during tests, keeping the process efficient and clean. Adopting a flexible mindset towards TCP connections and understanding system behavior will ultimately lead to better server performance and cleaner tests.



By taking these steps, you can mitigate the chances of encountering unclosed HTTP connections and streamline your Node.js testing process skillfully.