How Can You Effectively Diagnose 404 Errors When Serving Files with http.FileServer?

Diagnosing 404 Errors with HTTP File Serving

In HTTP applications, it's crucial to handle errors effectively to provide a reliable user experience. When serving files using http.FileServer, unexpected requests for nonexistent files can arise, leaving the server console devoid of error logs.

To address this, we can extend the handler functionality provided by http.StripPrefix() and http.FileServer(). By wrapping these handlers in our custom logic, we gain the ability to intercept HTTP responses and inspect their status codes.

To achieve this, we require a method to capture the response status code, as it's not directly accessible with http.ResponseWriter. We introduce a wrapper, StatusRespWr, which embeds http.ResponseWriter and stores the status code internally.

Our custom handler, wrapHandler(), intercepts the request and response. It utilizes StatusRespWr to retrieve the status code after the request is processed by the original handler. If the status code indicates an error (400 or higher), we log the incident along with the path of the requested file.

To implement this logging functionality, we wrap the original handler and register it as shown in the code snippet below:

<code class="go">http.HandleFunc("/o/", wrapHandler(
    http.StripPrefix("/o", http.FileServer(http.Dir("/test")))))</code>

By running this modified file server, we now receive informative logs for nonexistent files, ensuring visibility into potential issues:

<code class="text">2015/12/01 11:47:40 Error status code: 404 when serving path: /o/sub/b.txt2</code>

With this enhancement, server administrators can proactively monitor and address potential problems related to incorrect URLs or missing files.

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