зеркало из https://github.com/golang/image.git
70 строки
1.4 KiB
Go
70 строки
1.4 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
package tiff
|
|
|
|
import "io"
|
|
|
|
// buffer buffers an io.Reader to satisfy io.ReaderAt.
|
|
type buffer struct {
|
|
r io.Reader
|
|
buf []byte
|
|
}
|
|
|
|
// fill reads data from b.r until the buffer contains at least end bytes.
|
|
func (b *buffer) fill(end int) error {
|
|
m := len(b.buf)
|
|
if end > m {
|
|
if end > cap(b.buf) {
|
|
newcap := 1024
|
|
for newcap < end {
|
|
newcap *= 2
|
|
}
|
|
newbuf := make([]byte, end, newcap)
|
|
copy(newbuf, b.buf)
|
|
b.buf = newbuf
|
|
} else {
|
|
b.buf = b.buf[:end]
|
|
}
|
|
if n, err := io.ReadFull(b.r, b.buf[m:end]); err != nil {
|
|
end = m + n
|
|
b.buf = b.buf[:end]
|
|
return err
|
|
}
|
|
}
|
|
return nil
|
|
}
|
|
|
|
func (b *buffer) ReadAt(p []byte, off int64) (int, error) {
|
|
o := int(off)
|
|
end := o + len(p)
|
|
if int64(end) != off+int64(len(p)) {
|
|
return 0, io.ErrUnexpectedEOF
|
|
}
|
|
|
|
err := b.fill(end)
|
|
return copy(p, b.buf[o:end]), err
|
|
}
|
|
|
|
// Slice returns a slice of the underlying buffer. The slice contains
|
|
// n bytes starting at offset off.
|
|
func (b *buffer) Slice(off, n int) ([]byte, error) {
|
|
end := off + n
|
|
if err := b.fill(end); err != nil {
|
|
return nil, err
|
|
}
|
|
return b.buf[off:end], nil
|
|
}
|
|
|
|
// newReaderAt converts an io.Reader into an io.ReaderAt.
|
|
func newReaderAt(r io.Reader) io.ReaderAt {
|
|
if ra, ok := r.(io.ReaderAt); ok {
|
|
return ra
|
|
}
|
|
return &buffer{
|
|
r: r,
|
|
buf: make([]byte, 0, 1024),
|
|
}
|
|
}
|