copyBuffer := make([]byte, 128)
	for l := 0; l < 10; l++ {
		for fail := 1; fail <= 256; fail *= 2 {
			// Fail after 'fail' writes
			ew := &errorWriter{N: fail}
			w, err := NewWriter(ew, l)
			if err != nil {
				t.Fatalf("NewWriter: level %d: %v", l, err)
			}
			n, err := io.CopyBuffer(w, struct{ io.Reader }{bytes.NewBuffer(in)}, copyBuffer)
			if err == nil {

func CopyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) {
	if buf != nil && len(buf) == 0 {
		panic("empty buffer in CopyBuffer")
	}
	return copyBuffer(dst, src, buf)
}

// copyBuffer is the actual implementation of Copy and CopyBuffer.
// if buf is nil, one is allocated.
func copyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) {

	r2 := strings.NewReader("second reader\n")
	buf := make([]byte, 8)

	// buf is used here...
	if _, err := io.CopyBuffer(os.Stdout, r1, buf); err != nil {
		log.Fatal(err)
	}

	// ... reused here also. No need to allocate an extra buffer.
	if _, err := io.CopyBuffer(os.Stdout, r2, buf); err != nil {
		log.Fatal(err)
	}

	// Output:
	// first reader
	// second reader
}

	rb := new(Buffer)
	wb := new(Buffer)
	rb.WriteString("hello, world.")
	CopyBuffer(wb, rb, make([]byte, 1)) // Tiny buffer to keep it honest.
	if wb.String() != "hello, world." {
		t.Errorf("CopyBuffer did not work properly")
	}
}

func TestCopyBufferNil(t *testing.T) {
	rb := new(Buffer)
	wb := new(Buffer)
	rb.WriteString("hello, world.")
	CopyBuffer(wb, rb, nil) // Should allocate a buffer.
	if wb.String() != "hello, world." {

		zw.Reset(&b)
		if _, err := io.CopyBuffer(zw, &r, buf); err != nil {
			log.Fatal(err)
		}
		if err := zw.Close(); err != nil {
			log.Fatal(err)
		}

		// Reset the decompressor and decode to some output stream.
		if err := zr.(flate.Resetter).Reset(&b, nil); err != nil {
			log.Fatal(err)
		}
		if _, err := io.CopyBuffer(os.Stdout, zr, buf); err != nil {
			log.Fatal(err)
		}

			output := strings.Repeat(test.enc, multiplier)

			var buf bytes.Buffer
			enc := NewEncoder(&buf)
			r := struct{ io.Reader }{bytes.NewReader(input)} // io.Reader only; not io.WriterTo
			if n, err := io.CopyBuffer(enc, r, make([]byte, 7)); n != int64(len(input)) || err != nil {
				t.Errorf("encoder.Write(%q*%d) = (%d, %v), want (%d, nil)", test.dec, multiplier, n, err, len(input))
				continue
			}

	var buf []byte
	if p.BufferPool != nil {
		buf = p.BufferPool.Get()
		defer p.BufferPool.Put(buf)
	}
	_, err := p.copyBuffer(w, src, buf)
	return err
}

// copyBuffer returns any write errors or non-EOF read errors, and the amount
// of bytes written.
func (p *ReverseProxy) copyBuffer(dst io.Writer, src io.Reader, buf []byte) (int64, error) {
	if len(buf) == 0 {
		buf = make([]byte, 32*1024)
	}

	for i, r := range mr.readers {
		var n int64
		if subMr, ok := r.(*multiReader); ok { // reuse buffer with nested multiReaders
			n, err = subMr.writeToWithBuffer(w, buf)
		} else {
			n, err = copyBuffer(w, r, buf)
		}
		sum += n
		if err != nil {
			mr.readers = mr.readers[i:] // permit resume / retry after error
			return sum, err
		}
		mr.readers[i] = nil // permit early GC
	}
	mr.readers = nil

	bufCap := cap(buf1)
	buf := buf1[0:bufCap:bufCap]

	// For netstack: src is a gonet.Conn, doesn't implement WriterTo. Dst is a net.TcpConn - and implements ReadFrom.
	// CopyBuffered is the actual implementation of Copy and CopyBuffer.
	// if buf is nil, one is allocated.
	// Duplicated from io

	// This will prevent stats from working.
	// If the reader has a WriteTo method, use it to do the copy.
	// Avoids an allocation and a copy.

			// Read's failed for object with right size, file is corrupt.
			return err
		}
		// Subtract hash length..
		left -= int64(n)
		if left < shardSize {
			shardSize = left
		}

		read, err := io.CopyBuffer(h, io.LimitReader(r, shardSize), *bufp)
		if err != nil {
			// Read's failed for object with right size, at different offsets.
			return errFileCorrupt
		}

		left -= read