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