Expose the underlying behavior through a ReadSeekStater interface

js/modules/k6/experimental/fs/module.go

@@ -7,6 +7,7 @@ package fs
 import (
 	"errors"
 	"fmt"
+	"io"
 	"reflect"
 
 	"github.com/grafana/sobek"
@@ -136,7 +137,7 @@ func (mi *ModuleInstance) openImpl(path string) (*File, error) {
 
 	file := &File{
 		Path: path,
-		Impl: file{
+		ReadSeekStater: &file{
 			path: path,
 			data: data,
 		},
@@ -147,6 +148,26 @@ func (mi *ModuleInstance) openImpl(path string) (*File, error) {
 	return file, nil
 }
 
+// Stater is an interface that provides information about a file.
+//
+// Although in the context of this module we have a single implementation
+// of this interface, it is defined to allow exposing the `file`'s behavior
+// to other module through the `ReadSeekStater` interface without having to
+// leak our internal abstraction.
+type Stater interface {
+	// Stat returns a FileInfo describing the named file.
+	Stat() *FileInfo
+}
+
+// ReadSeekStater is an interface that combines the io.ReadSeeker and Stater
+// interfaces and ensure that structs implementing it have the necessary
+// methods to interact with files.
+type ReadSeekStater interface {
+	io.Reader
+	io.Seeker
+	Stater
+}
+
 // File represents a file and exposes methods to interact with it.
 //
 // It is a wrapper around the [file] struct, which is meant to be directly
@@ -162,7 +183,7 @@ type File struct {
 	// implementation details, but keep it public so that we can access it
 	// from other modules that would want to leverage its implementation of
 	// io.Reader and io.Seeker.
-	Impl file `js:"-"`
+	ReadSeekStater ReadSeekStater `js:"-"`
 
 	// vu holds a reference to the VU this file is associated with.
 	//
@@ -182,7 +203,7 @@ func (f *File) Stat() *sobek.Promise {
 	promise, resolve, _ := promises.New(f.vu)
 
 	go func() {
-		resolve(f.Impl.stat())
+		resolve(f.ReadSeekStater.Stat())
 	}()
 
 	return promise
@@ -227,7 +248,7 @@ func (f *File) Read(into sobek.Value) *sobek.Promise {
 	// occurs on the main thread, during the promise's resolution.
 	callback := f.vu.RegisterCallback()
 	go func() {
-		n, readErr := f.Impl.Read(buffer)
+		n, readErr := f.ReadSeekStater.Read(buffer)
 		callback(func() error {
 			_ = copy(intoBytes[0:n], buffer)
 
@@ -290,7 +311,7 @@ func (f *File) Seek(offset sobek.Value, whence sobek.Value) *sobek.Promise {
 
 	callback := f.vu.RegisterCallback()
 	go func() {
-		newOffset, err := f.Impl.Seek(intOffset, seekMode)
+		newOffset, err := f.ReadSeekStater.Seek(intOffset, seekMode)
 		callback(func() error {
 			if err != nil {
 				reject(err)