add fsext bridge

Signed-off-by: Pablo Chacin <pablochacin@gmail.com>

Author: pablochacin

lib/fsext/bridge.go

@@ -0,0 +1,27 @@
+package fsext
+
+import (
+	"fmt"
+	"io/fs"
+)
+
+// IOFSBridge allows an afero.Fs to implement the Go standard library io/fs.FS.
+type IOFSBridge struct {
+	FSExt Fs
+}
+
+// NewIOFSBridge returns an IOFSBridge from a Fs
+func NewIOFSBridge(fs Fs) fs.FS {
+	return &IOFSBridge{
+		FSExt: fs,
+	}
+}
+
+// Open implements fs.Fs Open
+func (b *IOFSBridge) Open(name string) (fs.File, error) {
+	f, err := b.FSExt.Open(name)
+	if err != nil {
+		return nil, fmt.Errorf("opening file %w", err)
+	}
+	return f, nil
+}

lib/fsext/bridge_test.go

@@ -0,0 +1,31 @@
+package fsext
+
+import (
+	"io"
+	"io/fs"
+	"testing"
+
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestBridgeOpen(t *testing.T) {
+	t.Parallel()
+
+	testfs := afero.NewMemMapFs()
+	require.NoError(t, WriteFile(testfs, "abasicpath/onetwo.txt", []byte(`test123`), 0o644))
+
+	bridge := &IOFSBridge{FSExt: testfs}
+
+	// it asserts that bridge implements io/fs.FS
+	goiofs := fs.FS(bridge)
+	f, err := goiofs.Open("abasicpath/onetwo.txt")
+	require.NoError(t, err)
+	require.NotNil(t, f)
+
+	content, err := io.ReadAll(f)
+	require.NoError(t, err)
+
+	assert.Equal(t, "test123", string(content))
+}