rclone/vendor/storj.io/common/ranger/reader.go

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2020-05-11 20:57:46 +02:00
// Copyright (C) 2019 Storj Labs, Inc.
// See LICENSE for copying information.
package ranger
import (
"bytes"
"context"
"io"
"io/ioutil"
"storj.io/common/readcloser"
)
// A Ranger is a flexible data stream type that allows for more effective
// pipelining during seeking. A Ranger can return multiple parallel Readers for
// any subranges.
type Ranger interface {
Size() int64
Range(ctx context.Context, offset, length int64) (io.ReadCloser, error)
}
// ByteRanger turns a byte slice into a Ranger
type ByteRanger []byte
// Size implements Ranger.Size
func (b ByteRanger) Size() int64 { return int64(len(b)) }
// Range implements Ranger.Range
func (b ByteRanger) Range(ctx context.Context, offset, length int64) (_ io.ReadCloser, err error) {
defer mon.Task()(&ctx)(&err)
if offset < 0 {
return nil, Error.New("negative offset")
}
if length < 0 {
return nil, Error.New("negative length")
}
if offset+length > int64(len(b)) {
return nil, Error.New("buffer runoff")
}
return ioutil.NopCloser(bytes.NewReader(b[offset : offset+length])), nil
}
type concatReader struct {
r1 Ranger
r2 Ranger
}
func (c *concatReader) Size() int64 {
return c.r1.Size() + c.r2.Size()
}
func (c *concatReader) Range(ctx context.Context, offset, length int64) (_ io.ReadCloser, err error) {
defer mon.Task()(&ctx)(&err)
r1Size := c.r1.Size()
if offset+length <= r1Size {
return c.r1.Range(ctx, offset, length)
}
if offset >= r1Size {
return c.r2.Range(ctx, offset-r1Size, length)
}
r1Range, err := c.r1.Range(ctx, offset, r1Size-offset)
if err != nil {
return nil, err
}
return readcloser.MultiReadCloser(
r1Range,
readcloser.LazyReadCloser(func() (io.ReadCloser, error) {
return c.r2.Range(ctx, 0, length-(r1Size-offset))
})), nil
}
func concat2(r1, r2 Ranger) Ranger {
return &concatReader{r1: r1, r2: r2}
}
// Concat concatenates Rangers
func Concat(r ...Ranger) Ranger {
switch len(r) {
case 0:
return ByteRanger(nil)
case 1:
return r[0]
case 2:
return concat2(r[0], r[1])
default:
mid := len(r) / 2
return concat2(Concat(r[:mid]...), Concat(r[mid:]...))
}
}
type subrange struct {
r Ranger
offset, length int64
}
// Subrange returns a subset of a Ranger.
func Subrange(data Ranger, offset, length int64) (Ranger, error) {
dSize := data.Size()
if offset < 0 || offset > dSize {
return nil, Error.New("invalid offset")
}
if length+offset > dSize {
return nil, Error.New("invalid length")
}
return &subrange{r: data, offset: offset, length: length}, nil
}
func (s *subrange) Size() int64 {
return s.length
}
func (s *subrange) Range(ctx context.Context, offset, length int64) (_ io.ReadCloser, err error) {
defer mon.Task()(&ctx)(&err)
return s.r.Range(ctx, offset+s.offset, length)
}