使用Golang中的regexp从URL提取子域

Question

In the code sample below, I use regex to extract the subdomain name from a given URL. This sample works, but I don't think I've done it correctly at the point where I compile the regex, mainly where I insert the 'virtualHost' variable. Any suggestions?

package main

import (
    "fmt"
    "regexp"
)

var (
    virtualHost string
    domainRegex *regexp.Regexp
)

func extractSubdomain(host string) string {
    matches := domainRegex.FindStringSubmatch(host)
    if matches != nil && len(matches) > 1 {
        return matches[1]
    }
    return ""
}

func init() {
    // virtualHost = os.GetEnv("VIRTUAL_HOST")
    virtualHost = "login.localhost:3000"

    domainRegex = regexp.MustCompile(`^(?:https?://)?([-a-z0-9]+)(?:\.` + virtualHost + `)*$`)
}

func main() {
    // host := req.host
    host := "http://acme.login.localhost:3000"

    if result := extractSubdomain(host); result != "" {
        fmt.Printf("Subdomain detected: %s
", result)
        return
    }

    fmt.Println("No subdomain detected")
}

Answer 1

The url package has a function parse that allows you to parse an URL. The parsed URL instance has a method Hostname which will return you the hostname.

package main

import (
    "fmt"
    "log"
    "net/url"
)

func main() {
    u, err := url.Parse("http://login.localhost:3000")
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(u.Hostname())
}

Output:

login.localhost

See https://play.golang.com/p/3R1TPyk8qck