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How to Implement a Custom 404 Error Page in Go's Standard HTTP Package?
How to Implement a Custom 404 Error Page in Go's Standard HTTP Package?
Dec 28, 2024 am 08:59 AM
Showing Custom 404 Error Page with Standard HTTP Package
HTTP servers typically display a basic "404 page not found" error message when a user requests a non-existent URL. To provide a more informative or customized experience, it's necessary to implement a custom error page handler.
In the standard HTTP package for Go, there exists a mechanism to handle all non-handled requests and display a custom error page. Let's delve into how to achieve this:
Custom Error Handler Function
Create a function to handle the custom error page. This function takes three arguments:
- w (http.ResponseWriter): Response writer used to send the custom error page.
- r (*http.Request): Request object for the non-existing URL.
- status (int): Status code of the error (usually http.StatusNotFound).
func errorHandler(w http.ResponseWriter, r *http.Request, status int) {
// Set the HTTP status code.
w.WriteHeader(status)
// Customize the error response for specific status codes.
if status == http.StatusNotFound {
fmt.Fprint(w, "Custom 404 error message")
}
}
Setting the Custom Error Handler
The error handler function needs to be linked to the HTTP server. This is done in the http.ListenAndServe function, which starts the server on a specified port.
http.ListenAndServe(":12345", nil)
Replace nil with a custom HTTP request handler that handles all requests.
http.ListenAndServe(":12345", new(http.ServeMux))
In ServeMux, add the original route handlers for specific URLs.
mux := http.NewServeMux()
mux.HandleFunc("/smth/", smthHandler)
mux.HandleFunc("/", homeHandler)
http.ListenAndServe(":12345", mux)
Finally, add a NotFoundHandler to the ServeMux to handle all other URLs not handled by the specific route handlers.
mux.NotFoundHandler = http.HandlerFunc(errorHandler)
Example Code
The complete example code that implements the above approach is as follows:
package main
import (
"fmt"
"net/http"
)
func main() {
mux := http.NewServeMux()
mux.HandleFunc("/smth/", smthHandler)
mux.HandleFunc("/", homeHandler)
mux.NotFoundHandler = http.HandlerFunc(errorHandler)
http.ListenAndServe(":12345", mux)
}
func smthHandler(w http.ResponseWriter, r *http.Request) {
if r.URL.Path != "/smth/" {
errorHandler(w, r, http.StatusNotFound)
return
}
fmt.Fprint(w, "Welcome to smth")
}
func homeHandler(w http.ResponseWriter, r *http.Request) {
if r.URL.Path != "/" {
errorHandler(w, r, http.StatusNotFound)
return
}
fmt.Fprint(w, "Welcome home")
}
func errorHandler(w http.ResponseWriter, r *http.Request, status int) {
w.WriteHeader(status)
if status == http.StatusNotFound {
fmt.Fprint(w, "Custom 404 error message")
}
}
This code defines route handlers for specific URLs (/smth/ and /) and assigns a custom error handler function (errorHandler) to handle all other non-handled requests. When a user tries to access a non-existing URL, the custom 404 error page will be displayed instead of the default "404 page not found" message.
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