rewrite: Don't add / in Caddyfile, do it after replacer (#6662)

Author: francislavoie

modules/caddyhttp/rewrite/caddyfile.go

@@ -110,9 +110,6 @@ func parseCaddyfileURI(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, err
 			return nil, h.ArgErr()
 		}
 		rewr.StripPathPrefix = args[1]
-		if !strings.HasPrefix(rewr.StripPathPrefix, "/") {
-			rewr.StripPathPrefix = "/" + rewr.StripPathPrefix
-		}
 
 	case "strip_suffix":
 		if len(args) != 2 {

modules/caddyhttp/rewrite/rewrite.go

@@ -259,6 +259,9 @@ func (rewr Rewrite) Rewrite(r *http.Request, repl *caddy.Replacer) bool {
 	// strip path prefix or suffix
 	if rewr.StripPathPrefix != "" {
 		prefix := repl.ReplaceAll(rewr.StripPathPrefix, "")
+		if !strings.HasPrefix(prefix, "/") {
+			prefix = "/" + prefix
+		}
 		mergeSlashes := !strings.Contains(prefix, "//")
 		changePath(r, func(escapedPath string) string {
 			escapedPath = caddyhttp.CleanPath(escapedPath, mergeSlashes)

modules/caddyhttp/rewrite/rewrite_test.go

@@ -235,6 +235,11 @@ func TestRewrite(t *testing.T) {
 			input:  newRequest(t, "GET", "/prefix/foo/bar"),
 			expect: newRequest(t, "GET", "/foo/bar"),
 		},
+		{
+			rule:   Rewrite{StripPathPrefix: "prefix"},
+			input:  newRequest(t, "GET", "/prefix/foo/bar"),
+			expect: newRequest(t, "GET", "/foo/bar"),
+		},
 		{
 			rule:   Rewrite{StripPathPrefix: "/prefix"},
 			input:  newRequest(t, "GET", "/prefix"),