storj/pkg/ranger/reader.go

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// Copyright (C) 2019 Storj Labs, Inc.
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// See LICENSE for copying information.
package ranger
import (
"bytes"
"context"
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"io"
"io/ioutil"
"storj.io/storj/internal/readcloser"
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)
// 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)
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}
// ByteRanger turns a byte slice into a Ranger
type ByteRanger []byte
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// Size implements Ranger.Size
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func (b ByteRanger) Size() int64 { return int64(len(b)) }
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// Range implements Ranger.Range
func (b ByteRanger) Range(ctx context.Context, offset, length int64) (io.ReadCloser, error) {
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if offset < 0 {
return nil, Error.New("negative offset")
}
if length < 0 {
return nil, Error.New("negative length")
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}
if offset+length > int64(len(b)) {
return nil, Error.New("buffer runoff")
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}
return ioutil.NopCloser(bytes.NewReader(b[offset : offset+length])), nil
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}
type concatReader struct {
r1 Ranger
r2 Ranger
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}
func (c *concatReader) Size() int64 {
return c.r1.Size() + c.r2.Size()
}
func (c *concatReader) Range(ctx context.Context, offset, length int64) (io.ReadCloser, error) {
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r1Size := c.r1.Size()
if offset+length <= r1Size {
return c.r1.Range(ctx, offset, length)
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}
if offset >= r1Size {
return c.r2.Range(ctx, offset-r1Size, length)
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}
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
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}
func concat2(r1, r2 Ranger) Ranger {
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return &concatReader{r1: r1, r2: r2}
}
// Concat concatenates Rangers
func Concat(r ...Ranger) Ranger {
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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
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offset, length int64
}
// Subrange returns a subset of a Ranger.
func Subrange(data Ranger, offset, length int64) (Ranger, error) {
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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, error) {
return s.r.Range(ctx, offset+s.offset, length)
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}