How to use regexp get url pattern in golang?

Question

How to use regular expression matching URL, which does decide to use the corresponding function processing

package main

import(
  "fmt"
  "net/http"
)

func main() {
  http.HandleFunc("/pattern", resolve)
  http.ListenAndServe(":8080", nil)
}

func resolve(w http.ResponseWriter, r * http.Request) {
  fmt.Println(r.URL.Host)
}

Answer 1

http.HandleFunc() can not be used to register a pattern to match a regular expression. In short, the pattern specified at HandleFunc() can match a fixed, rooted path (like /favico.ico) or rooted subtrees (like /images/), longer patterns take precedence over shorter ones. You can find more details at the doc of the ServeMux type.

What you can do is register your handler to a rooted subtree which may be everything with the / pattern, and inside your handler you can do further regexp matching and routing.

For example:

func main() {
    http.HandleFunc("/", route) // Match everything
    http.ListenAndServe(":8080", nil)
}

var rNum = regexp.MustCompile(`\d`)  // Has digit(s)
var rAbc = regexp.MustCompile(`abc`) // Contains "abc"

func route(w http.ResponseWriter, r *http.Request) {
    switch {
    case rNum.MatchString(r.URL.Path):
        digits(w, r)
    case rAbc.MatchString(r.URL.Path):
        abc(w, r)
    default:
        w.Write([]byte("Unknown Pattern"))
    }
}

func digits(w http.ResponseWriter, r *http.Request) {
    w.Write([]byte("Has digits"))
}

func abc(w http.ResponseWriter, r *http.Request) {
    w.Write([]byte("Has abc"))
}

Or use an external library like Gorilla MUX.

Answer 2

I use github.com/gorilla/mux package. So router looks like:

func main() {

    r := mux.NewRouter()

    r.HandleFunc("/{name:pattern}", handle)
    http.ListenAndServe(":8080", r)
}

where {name:pattern} could be simply {slug} (without pattern) or {id:[0-9]+} or combination of them /{category}/{id:[0-9]+}. And get them in handler func:

func handle(w http.ResponseWriter, r *http.Request) {

    params := mux.Vars(r)

    // for /{category}/{id:[0-9]+} pattern
    category := params["category"]
    id := params["id"]
}

run it and try curl http://localhost:8080/whatever/1