vfs: add test for 0 length files read in the way mount does

vfs/write_test.go

@@ -2,6 +2,7 @@ package vfs
 
 import (
 	"context"
+	"io"
 	"os"
 	"sync"
 	"testing"
@@ -286,3 +287,32 @@ func TestWriteFileModTimeWithOpenWriters(t *testing.T) {
 		assert.Equal(t, info.ModTime().Unix(), mtime.Unix())
 	}
 }
+
+func TestFileZeroLength(t *testing.T) {
+	r := fstest.NewRun(t)
+	defer r.Finalise()
+	vfs, fh := writeHandleCreate(t, r)
+
+	// Close the file without writing to it
+	err := fh.Close()
+	if errors.Cause(err) == fs.ErrorCantUploadEmptyFiles {
+		t.Logf("skipping test: %v", err)
+		return
+	}
+	assert.NoError(t, err)
+
+	// read the 0 length file back in using ReadAt into a buffer
+	// this simulates what mount does
+	rd, err := vfs.OpenFile("file1", os.O_RDONLY, 0)
+	require.NoError(t, err)
+
+	buf := make([]byte, 1024)
+	n, err := rd.ReadAt(buf, 0)
+	if err != io.EOF {
+		assert.NoError(t, err)
+	}
+	assert.Equal(t, 0, n)
+
+	err = rd.Close()
+	assert.NoError(t, err)
+}