OnlineLibrary

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package buffer
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import (
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	"bytes"
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	"fmt"
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	"io"
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)
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const default_buffer_size = 1024 * 16
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type Reader struct {
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	source           io.ReadSeeker
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	nReadsFromSource int64
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	buffer           []byte
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	br               *bytes.Reader
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	lastErr          error
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}
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func NewReader(src io.ReadSeeker) *Reader {
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	return NewReaderSize(src, default_buffer_size)
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}
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func NewReaderSize(src io.ReadSeeker, bufSize int) *Reader {
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	r := new(Reader)
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	r.source = src
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	r.buffer = make([]byte, bufSize)
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	r.br = bytes.NewReader(nil)
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	return r
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}
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func (r *Reader) Read(p []byte) (int, error) {
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	if len(p) == 0 {
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		return 0, io.ErrShortBuffer
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	}
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	if r.br.Len() == 0 {
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		if r.lastErr != nil {
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			return 0, r.lastErr
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		}
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		var n int
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		n, r.lastErr = r.source.Read(r.buffer)
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		if n == 0 {
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			return 0, r.lastErr
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		}
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		r.nReadsFromSource += int64(n)
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		r.br.Reset(r.buffer[:n])
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	}
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	return r.br.Read(p)
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}
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func (r *Reader) Seek(offset int64, whence int) (int64, error) {
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	if offset < 0 {
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		return 0, fmt.Errorf("negative offset not supported")
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	}
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	if whence != io.SeekStart {
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		return 0, fmt.Errorf("whence %v not supported", whence)
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	}
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	r.br.Reset(nil)
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	sourceOffset, err := r.source.Seek(offset, io.SeekStart)
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	if err != nil {
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		r.lastErr = err
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	}
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	r.nReadsFromSource = sourceOffset
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	return sourceOffset, err
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}
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