Rewrite: A Simple and Powerful URL Rewriter for Go

Rewrite is a Go package that lets you rewrite URL paths, subdomains or hosts based on regular expressions. It is inspired by Apache's mod_rewrite module and can be used as a middleware for net/http.

Rewrite can help you achieve better SEO results by redirecting old or unwanted URLs to new ones, enforcing a primary subdomain, or simplifying complex URL structures.

How to Install Rewrite

To install Rewrite, you need to have Go installed on your system. Then, you can use the go get command to download and install the package:

$ go get github.com/kataras/rewrite

How to Use Rewrite

You can load rewrite options in two ways:

1. Through code using the New function and Handler method. This way, you can handle parse errors and create rules programmatically.
2. Or through a YAML file using the Load function which returns a func(http.Handler) http.Handler. This is the most common and simplest way. It panics on parse errors.

The syntax of the rewrite rules is:

REDIRECT_CODE_DIGITS PATTERN_REGEX TARGET_REPL

Where:

• REDIRECT_CODE_DIGITS is the HTTP status code to use for the redirection, such as 301 (Moved Permanently) or 302 (Found).
• PATTERN_REGEX is the regular expression that matches the request URL path, subdomain or host.
• TARGET_REPL is the replacement string that contains the new URL path, subdomain or host.

For example:

301 /seo/(.*) /$1

This rule redirects all requests from relative path /seo/* to /* using the 301 HTTP status code.

You can also use a special option called PrimarySubdomain to redirect all requests from the root domain to a specific subdomain, such as www.

For example:

PrimarySubdomain: www

This option redirects all requests from example.com to www.example.com.

Examples

Let's write a simple application that follows these redirect rules:

• Redirects /seo/* to /*
• Redirects /docs/v12* to /docs
• Redirects /old (.*) to /
• Redirects root domain requests to www.

The code would look like this:

package main

import (
    "net/http"

    "github.com/kataras/rewrite"
)

func main() {
    mux := http.NewServeMux()
    // [...routes]

    // Load the redirect rules from a YAML file.
    redirects := rewrite.Load("redirects.yml")

    // Wrap the router with the rewrite middleware.
    http.ListenAndServe(":8080", redirects(mux))
}

The YAML file would look like this:

RedirectMatch:
  # Redirects /seo/* to /*
  - 301 /seo/(.*) /$1
  # Redirects /docs/v12* to /docs
  - 301 /docs/v12(.*) /docs
  # Redirects /old (.*) to /
  - 301 /old(.*) /
# Redirects root domain requests to www.
PrimarySubdomain: www

That's it! Now you can test your application and see how it redirects the requests according to your rules.

You can find more examples in the _examples folder of the GitHub repository: https://github.com/kataras/rewrite/tree/main/_examples

Conclusion

Rewrite is a handy package that lets you rewrite URLs in Go with ease. It is compatible with any net/http router or framework and supports regular expressions for flexible matching and replacing. It can help you improve your SEO performance by redirecting old or unwanted URLs to new ones, enforcing a primary subdomain, or simplifying complex URL structures.

If you want to learn more about Rewrite, you can check out its GitHub repository: https://github.com/kataras/rewrite

I hope you enjoyed this article and found it useful. If you have any feedback or questions, feel free to leave a comment below. Thank you for reading! 😊