forked from grailbio/base
/
range.go
70 lines (64 loc) · 1.53 KB
/
range.go
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// Copyright 2017 GRAIL, Inc. All rights reserved.
// Use of this source code is governed by the Apache-2.0
// license that can be found in the LICENSE file.
package deprecated
import "io"
// RangeReader represents an io.ReadSeeker that operates over a restricted
// range of the supplied ReadSeeker. Reading and Seeking are consequently
// relative to the start of the range used to create the RangeReader.
type RangeReader struct {
rs io.ReadSeeker
start, pos, end int64
}
// NewRangeReader returns a new RangedReader.
func NewRangeReader(rs io.ReadSeeker, offset, length int64) (io.ReadSeeker, error) {
_, err := rs.Seek(offset, io.SeekStart)
if err != nil {
return nil, err
}
return &RangeReader{
rs: rs,
start: offset,
pos: offset,
end: offset + length,
}, nil
}
// Read implements io.Read.
func (rr *RangeReader) Read(buf []byte) (int, error) {
var eof error
size := int64(len(buf))
if rr.pos+size >= rr.end {
size = rr.end - rr.pos
eof = io.EOF
}
n, err := rr.rs.Read(buf[:size])
if err == nil {
err = eof
}
rr.pos += int64(n)
return n, err
}
// Seek implements io.Seek.
func (rr *RangeReader) Seek(offset int64, whence int) (int64, error) {
pos := rr.start
switch whence {
case io.SeekStart:
pos += offset
case io.SeekCurrent:
pos = rr.pos + offset
case io.SeekEnd:
if offset > 0 {
offset = 0
}
pos = rr.end + offset
}
if pos > rr.end {
rr.pos = rr.end
return pos, nil
}
n, err := rr.rs.Seek(pos, io.SeekStart)
if err == nil {
rr.pos = n
}
return n - rr.start, err
}