Why is my Go HandleFunc Triggered Twice per Browser Request?

HandleFunc Triggered Multiple Times: Investigation and Resolution

In the context of a web server, the HandleFunc function plays a crucial role in handling incoming HTTP requests. However, a common issue that can arise is the function being called twice for a single request. This behavior can be particularly problematic if your program relies on incrementing a counter or performing actions based on request count.

Let's delve into the problem showcased by the code snippet provided. Upon loading port 8000 in a web browser, the hello function is invoked twice. The perplexing nature of this behavior becomes evident when using curl, which invokes the function only once.

Upon setting up a logging mechanism within the code, you will discover that the browser also requests /favicon.ico. This request is initiated by the browser to display a small icon or logo representing the website in the tab or address bar.

The solution to the problem lies in acknowledging the request for the favicon and handling it appropriately. Here's an updated version of the code that addresses this need:

package main

import (
    "fmt"
    "io"
    "log"
    "net/http"
)

func hello(w http.ResponseWriter, r *http.Request) {
    if r.RequestURI == "/favicon.ico" {
        w.WriteHeader(http.StatusNotFound)
        return
    }
    io.WriteString(w, "Hello world!")
    log.Println("hello.")
}

func main() {
    mux := http.NewServeMux()
    mux.HandleFunc("/", hello)
    http.ListenAndServe(":8000", mux)
}

This modification ensures that the favicon request is handled gracefully, resulting in the hello function being called only once for each webpage request.

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