mcp/Resource: Refactor URI Template Matching with uritemplate Library (#100)

1. Replaced the `uriTemplateToRegexp` function with the use of
[yosida95/uritemplate](https://github.com/yosida95/uritemplate) to
handle URI template matching as per the request.
2. Updated the relevant test cases to verify the new implementation and
fixed an invalid URI template (`"file:///{}/{a}/{b}"`) that doesn't
conform to RFC 6570 due to an empty `{}` expression.
3. Updated `go.mod` and `go.sum` to reflect the new dependency.

Fixes #11.

go.mod

@@ -4,5 +4,6 @@ go 1.23.0
 
 require (
 	github.com/google/go-cmp v0.7.0
+	github.com/yosida95/uritemplate/v3 v3.0.2
 	golang.org/x/tools v0.34.0
 )

go.sum

@@ -1,4 +1,6 @@
 github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
 github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
+github.com/yosida95/uritemplate/v3 v3.0.2 h1:Ed3Oyj9yrmi9087+NczuL5BwkIc4wvTb5zIM+UJPGz4=
+github.com/yosida95/uritemplate/v3 v3.0.2/go.mod h1:ILOh0sOhIJR3+L/8afwt/kE++YT040gmv5BQTMR2HP4=
 golang.org/x/tools v0.34.0 h1:qIpSLOxeCYGg9TrcJokLBG4KFA6d795g0xkBkiESGlo=
 golang.org/x/tools v0.34.0/go.mod h1:pAP9OwEaY1CAW3HOmg3hLZC5Z0CCmzjAF2UQMSqNARg=

mcp/resource.go

@@ -13,11 +13,11 @@ import (
 	"net/url"
 	"os"
 	"path/filepath"
-	"regexp"
 	"strings"
 
 	"github.com/modelcontextprotocol/go-sdk/internal/jsonrpc2"
 	"github.com/modelcontextprotocol/go-sdk/internal/util"
+	"github.com/yosida95/uritemplate/v3"
 )
 
 // A serverResource associates a Resource with its handler.
@@ -155,67 +155,10 @@ func fileRoot(root *Root) (_ string, err error) {
 }
 
 // Matches reports whether the receiver's uri template matches the uri.
-// TODO: use "github.com/yosida95/uritemplate/v3"
 func (sr *serverResourceTemplate) Matches(uri string) bool {
-	re, err := uriTemplateToRegexp(sr.resourceTemplate.URITemplate)
+	tmpl, err := uritemplate.New(sr.resourceTemplate.URITemplate)
 	if err != nil {
 		return false
 	}
-	return re.MatchString(uri)
-}
-
-func uriTemplateToRegexp(uriTemplate string) (*regexp.Regexp, error) {
-	pat := uriTemplate
-	var b strings.Builder
-	b.WriteByte('^')
-	seen := map[string]bool{}
-	for len(pat) > 0 {
-		literal, rest, ok := strings.Cut(pat, "{")
-		b.WriteString(regexp.QuoteMeta(literal))
-		if !ok {
-			break
-		}
-		expr, rest, ok := strings.Cut(rest, "}")
-		if !ok {
-			return nil, errors.New("missing '}'")
-		}
-		pat = rest
-		if strings.ContainsRune(expr, ',') {
-			return nil, errors.New("can't handle commas in expressions")
-		}
-		if strings.ContainsRune(expr, ':') {
-			return nil, errors.New("can't handle prefix modifiers in expressions")
-		}
-		if len(expr) > 0 && expr[len(expr)-1] == '*' {
-			return nil, errors.New("can't handle explode modifiers in expressions")
-		}
-
-		// These sets of valid characters aren't accurate.
-		// See https://datatracker.ietf.org/doc/html/rfc6570.
-		var re, name string
-		first := byte(0)
-		if len(expr) > 0 {
-			first = expr[0]
-		}
-		switch first {
-		default:
-			// {var} doesn't match slashes. (It should also fail to match other characters,
-			// but this simplified implementation doesn't handle that.)
-			re = `[^/]*`
-			name = expr
-		case '+':
-			// {+var} matches anything, even slashes
-			re = `.*`
-			name = expr[1:]
-		case '#', '.', '/', ';', '?', '&':
-			return nil, fmt.Errorf("prefix character %c unsupported", first)
-		}
-		if seen[name] {
-			return nil, fmt.Errorf("can't handle duplicate name %q", name)
-		}
-		seen[name] = true
-		b.WriteString(re)
-	}
-	b.WriteByte('$')
-	return regexp.Compile(b.String())
+	return tmpl.Regexp().MatchString(uri)
 }

mcp/resource_test.go

@@ -119,18 +119,14 @@ func TestTemplateMatch(t *testing.T) {
 		template string
 		want     bool
 	}{
-		{"file:///{}/{a}/{b}", true},
+		{"file:///{}/{a}/{b}", false}, // invalid: empty variable expression "{}" is not allowed in RFC 6570
 		{"file:///{a}/{b}", false},
 		{"file:///{+path}", true},
 		{"file:///{a}/{+path}", true},
 	} {
-		re, err := uriTemplateToRegexp(tt.template)
-		if err != nil {
-			t.Fatalf("%s: %v", tt.template, err)
-		}
-		got := re.MatchString(uri)
-		if got != tt.want {
-			t.Errorf("%s: got %t, want %t", tt.template, got, tt.want)
+		resourceTmpl := serverResourceTemplate{resourceTemplate: &ResourceTemplate{URITemplate: tt.template}}
+		if matched := resourceTmpl.Matches(uri); matched != tt.want {
+			t.Errorf("%s: got %t, want %t", tt.template, matched, tt.want)
 		}
 	}
 }