Regex router pattern not matching as expected.

[mmmmmrob]

This is probably me doing something wrong, as I'm new to go and chi, but any help would be really appreciated!

I am serving a URL in the form /test/f9772163-44e7-49b1-9c8c-36b8d023aa6b-2024-01-01 which is a UUID and date, separated by a -.

I hoped I could match this using a regex pattern in the router pattern string, but this fails to match.

r.Get("/test/{UUID:[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}}-{date}", func(w http.ResponseWriter, r *http.Request) {
	uuidParam := chi.URLParam(r, "UUID")
	dateParam := chi.URLParam(r, "date")
	w.Write([]byte(uuidParam + "\n" + dateParam))
})

Expected:

f9772163-44e7-49b1-9c8c-36b8d023aa6b
2024-01-01

Actual:

404 page not found

[mmmmmrob]

Digging further:

If I remove the date and only keep the trailing - I see the following:

Request /test/f9772163-44e7-49b1-9c8c-36b8d023aa6b-

// The trailing hyphen is WITHIN the uuid regex
r.Get("/test/{UUID:[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}-}", func(w http.ResponseWriter, r *http.Request) {
	uuidParam := chi.URLParam(r, "UUID")
	w.Write([]byte(uuidParam))
})

// successfully matches and returns f9772163-44e7-49b1-9c8c-36b8d023aa6b-

// The trailing hyphen is OUTSIDE the uuid regex
r.Get("/test/{UUID:[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}}-", func(w http.ResponseWriter, r *http.Request) {
	uuidParam := chi.URLParam(r, "UUID")
	w.Write([]byte(uuidParam))
})

// fails to match and returns 404 page not found

[EdenBW]

Chi looks for explicit literal matches (in this case the "-" between your UUID and date) before the group patterns, so it doesn't really know where any of the -'s belong.

You could use a different separator like "/" or "_", or write the URL parser yourself.

package main

import (
	"fmt"
	"log"
	"net/http"
	"strings"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"
)

func main() {
	r := chi.NewRouter()
	r.Use(middleware.Logger)

	// works when "-" appears only in 1 group
	r.Get("/test1/{group1:[0-9]{1}}-{group2:[0-9]{1}}", func(w http.ResponseWriter, r *http.Request) {
		group1 := chi.URLParam(r, "group1")
		group2 := chi.URLParam(r, "group2")
		w.Write([]byte(fmt.Sprintf("This works!\ngroup1: %s\ngroup2: %s\n", group1, group2)))
	})

	// works with multiple "-" but using "_" as a group separator
	r.Get("/test2/{group1:[0-9]{1}-[0-9]{1}}_{group2:[0-9]{1}}", func(w http.ResponseWriter, r *http.Request) {
		group1 := chi.URLParam(r, "group1")
		group2 := chi.URLParam(r, "group2")
		w.Write([]byte(fmt.Sprintf("This also works!\ngroup1: %s\ngroup2: %s\n", group1, group2)))
	})

	// won't work with a "-" appearing in a group AND as a separator
	r.Get("/test3/{group1:[0-9]{1}-[0-9]{1}}-{group2:[0-9]{1}}", func(w http.ResponseWriter, r *http.Request) {
		group1 := chi.URLParam(r, "group1")
		group2 := chi.URLParam(r, "group2")
		w.Write([]byte(fmt.Sprintf("This won't be reached!\ngroup1: %s\ngroup2: %s\n", group1, group2)))
	})

	// won't work with a "-" appearing in multiple groups
	r.Get("/test4/{group1:[0-9]{1}-[0-9]{1}}{group2:-[0-9]{1}}", func(w http.ResponseWriter, r *http.Request) {
		group1 := chi.URLParam(r, "group1")
		group2 := chi.URLParam(r, "group2")
		w.Write([]byte(fmt.Sprintf("This won't be reached!\ngroup1: %s\ngroup2: %s\n", group1, group2)))
	})

	// Optionally parse it yourself
	r.Get("/test5/{params}", func(w http.ResponseWriter, r *http.Request) {
		params := chi.URLParam(r, "params")
		parts := strings.Split(params, "-")
		group1 := strings.Join(parts[:2], "-")
		group2 := strings.Join(parts[2:], "-")
		w.Write([]byte(fmt.Sprintf("This walso works!\ngroup1: %s\ngroup2: %s\n", group1, group2)))
	})

	fmt.Println("Server starting on :3000")
	fmt.Println("Test URLs:")
	fmt.Println("1. http://localhost:3000/test1/1-1  (will work)")
	fmt.Println("2. http://localhost:3000/test2/1-1_1 (will work)")
	fmt.Println("3. http://localhost:3000/test3/1-1-1 (won't work)")
	fmt.Println("4. http://localhost:3000/test4/1-1-1 (won't work)")
	fmt.Println("5. http://localhost:3000/test5/1-1-1 (will work)")

	log.Fatal(http.ListenAndServe(":3000", r))
}