feat(config): add withFs option to file source (#2557)

Co-authored-by: Mohamed MHAMDI <mmhamdi@hubside.com>

config/source/file/file.go

@@ -3,12 +3,14 @@ package file
 
 import (
 	"io"
+	"io/fs"
 	"os"
 
 	"go-micro.dev/v4/config/source"
 )
 
 type file struct {
+	fs   fs.FS
 	path string
 	opts source.Options
 }
@@ -18,7 +20,15 @@ var (
 )
 
 func (f *file) Read() (*source.ChangeSet, error) {
-	fh, err := os.Open(f.path)
+	var fh fs.File
+	var err error
+
+	if f.fs != nil {
+		fh, err = f.fs.Open(f.path)
+	} else {
+		fh, err = os.Open(f.path)
+	}
+
 	if err != nil {
 		return nil, err
 	}
@@ -48,6 +58,11 @@ func (f *file) String() string {
 }
 
 func (f *file) Watch() (source.Watcher, error) {
+	// do not watch if fs.FS instance is provided
+	if f.fs != nil {
+		return source.NewNoopWatcher()
+	}
+
 	if _, err := os.Stat(f.path); err != nil {
 		return nil, err
 	}
@@ -60,10 +75,13 @@ func (f *file) Write(cs *source.ChangeSet) error {
 
 func NewSource(opts ...source.Option) source.Source {
 	options := source.NewOptions(opts...)
+
+	fs, _ := options.Context.Value(fsKey{}).(fs.FS)
+
 	path := DefaultPath
 	f, ok := options.Context.Value(filePathKey{}).(string)
 	if ok {
 		path = f
 	}
-	return &file{opts: options, path: path}
+	return &file{opts: options, fs: fs, path: path}
 }

config/source/file/file_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
+	"testing/fstest"
 	"time"
 
 	"go-micro.dev/v4/config"
@@ -64,3 +65,25 @@ func TestFile(t *testing.T) {
 		t.Error("data from file does not match")
 	}
 }
+
+func TestWithFS(t *testing.T) {
+	data := []byte(`{"foo": "bar"}`)
+	path := fmt.Sprintf("file.%d", time.Now().UnixNano())
+
+	fsMock := fstest.MapFS{
+		path: &fstest.MapFile{
+			Data: data,
+			Mode: 0666,
+		},
+	}
+
+	f := file.NewSource(file.WithFS(fsMock), file.WithPath(path))
+	c, err := f.Read()
+	if err != nil {
+		t.Error(err)
+	}
+	if string(c.Data) != string(data) {
+		t.Logf("%+v", c)
+		t.Error("data from file does not match")
+	}
+}

config/source/file/options.go

@@ -2,11 +2,13 @@ package file
 
 import (
 	"context"
+	"io/fs"
 
 	"go-micro.dev/v4/config/source"
 )
 
 type filePathKey struct{}
+type fsKey struct{}
 
 // WithPath sets the path to file
 func WithPath(p string) source.Option {
@@ -17,3 +19,13 @@ func WithPath(p string) source.Option {
 		o.Context = context.WithValue(o.Context, filePathKey{}, p)
 	}
 }
+
+// WithFS sets the underlying filesystem to lookup file from  (default os.FS)
+func WithFS(fs fs.FS) source.Option {
+	return func(o *source.Options) {
+		if o.Context == nil {
+			o.Context = context.Background()
+		}
+		o.Context = context.WithValue(o.Context, fsKey{}, fs)
+	}
+}