Break the fs package up into smaller parts.

The purpose of this is to make it easier to maintain and eventually to
allow the rclone backends to be re-used in other projects without
having to use the rclone configuration system.

The new code layout is documented in CONTRIBUTING.

lib/readers/repeatable_test.go

@@ -0,0 +1,100 @@
+package readers
+
+import (
+	"bytes"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestRepeatableReader(t *testing.T) {
+	var dst []byte
+	var n int
+	var pos int64
+	var err error
+
+	b := []byte("Testbuffer")
+	buf := bytes.NewBuffer(b)
+	r := NewRepeatableReader(buf)
+
+	dst = make([]byte, 100)
+	n, err = r.Read(dst)
+	assert.Nil(t, err)
+	assert.Equal(t, 10, n)
+	require.Equal(t, b, dst[0:10])
+
+	// Test read EOF
+	n, err = r.Read(dst)
+	assert.Equal(t, io.EOF, err)
+	assert.Equal(t, 0, n)
+
+	// Test Seek Back to start
+	dst = make([]byte, 10)
+	pos, err = r.Seek(0, 0)
+	assert.Nil(t, err)
+	require.Equal(t, 0, int(pos))
+
+	n, err = r.Read(dst)
+	assert.Nil(t, err)
+	assert.Equal(t, 10, n)
+	require.Equal(t, b, dst)
+
+	// Test partial read
+	buf = bytes.NewBuffer(b)
+	r = NewRepeatableReader(buf)
+	dst = make([]byte, 5)
+	n, err = r.Read(dst)
+	assert.Nil(t, err)
+	assert.Equal(t, 5, n)
+	require.Equal(t, b[0:5], dst)
+	n, err = r.Read(dst)
+	assert.Nil(t, err)
+	assert.Equal(t, 5, n)
+	require.Equal(t, b[5:], dst)
+
+	// Test Seek
+	buf = bytes.NewBuffer(b)
+	r = NewRepeatableReader(buf)
+	// Should not allow seek past cache index
+	pos, err = r.Seek(5, 1)
+	assert.NotNil(t, err)
+	assert.Equal(t, "fs.RepeatableReader.Seek: offset is unavailable", err.Error())
+	assert.Equal(t, 0, int(pos))
+
+	// Should not allow seek to negative position start
+	pos, err = r.Seek(-1, 1)
+	assert.NotNil(t, err)
+	assert.Equal(t, "fs.RepeatableReader.Seek: negative position", err.Error())
+	assert.Equal(t, 0, int(pos))
+
+	// Should not allow seek with invalid whence
+	pos, err = r.Seek(0, 3)
+	assert.NotNil(t, err)
+	assert.Equal(t, "fs.RepeatableReader.Seek: invalid whence", err.Error())
+	assert.Equal(t, 0, int(pos))
+
+	// Should seek from index with io.SeekCurrent(1) whence
+	dst = make([]byte, 5)
+	_, _ = r.Read(dst)
+	pos, err = r.Seek(-3, 1)
+	assert.Nil(t, err)
+	require.Equal(t, 2, int(pos))
+	pos, err = r.Seek(1, 1)
+	assert.Nil(t, err)
+	require.Equal(t, 3, int(pos))
+
+	// Should seek from cache end with io.SeekEnd(2) whence
+	pos, err = r.Seek(-3, 2)
+	assert.Nil(t, err)
+	require.Equal(t, 2, int(pos))
+
+	// Should read from seek postion and past it
+	dst = make([]byte, 5)
+	n, err = io.ReadFull(r, dst)
+	assert.Nil(t, err)
+	assert.Equal(t, 5, n)
+	assert.Equal(t, b[2:7], dst)
+
+}