90 lines
1.7 KiB
Go
90 lines
1.7 KiB
Go
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package chunkreader
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import (
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"io"
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)
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type ChunkReader struct {
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r io.Reader
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buf []byte
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rp, wp int // buf read position and write position
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options Options
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}
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type Options struct {
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MinBufLen int // Minimum buffer length
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}
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func NewChunkReader(r io.Reader) *ChunkReader {
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cr, err := NewChunkReaderEx(r, Options{})
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if err != nil {
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panic("default options can't be bad")
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}
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return cr
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}
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func NewChunkReaderEx(r io.Reader, options Options) (*ChunkReader, error) {
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if options.MinBufLen == 0 {
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options.MinBufLen = 4096
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}
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return &ChunkReader{
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r: r,
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buf: make([]byte, options.MinBufLen),
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options: options,
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}, nil
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}
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// Next returns buf filled with the next n bytes. If an error occurs, buf will
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// be nil.
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func (r *ChunkReader) Next(n int) (buf []byte, err error) {
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// n bytes already in buf
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if (r.wp - r.rp) >= n {
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buf = r.buf[r.rp : r.rp+n]
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r.rp += n
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return buf, err
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}
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// available space in buf is less than n
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if len(r.buf) < n {
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r.copyBufContents(r.newBuf(n))
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}
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// buf is large enough, but need to shift filled area to start to make enough contiguous space
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minReadCount := n - (r.wp - r.rp)
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if (len(r.buf) - r.wp) < minReadCount {
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newBuf := r.newBuf(n)
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r.copyBufContents(newBuf)
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}
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if err := r.appendAtLeast(minReadCount); err != nil {
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return nil, err
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}
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buf = r.buf[r.rp : r.rp+n]
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r.rp += n
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return buf, nil
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}
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func (r *ChunkReader) appendAtLeast(fillLen int) error {
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n, err := io.ReadAtLeast(r.r, r.buf[r.wp:], fillLen)
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r.wp += n
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return err
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}
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func (r *ChunkReader) newBuf(size int) []byte {
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if size < r.options.MinBufLen {
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size = r.options.MinBufLen
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}
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return make([]byte, size)
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}
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func (r *ChunkReader) copyBufContents(dest []byte) {
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r.wp = copy(dest, r.buf[r.rp:r.wp])
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r.rp = 0
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r.buf = dest
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}
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