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." {

			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)
	}

	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

			}
			// os.File.ReadFrom will allocate its own copy buffer if we let io.Copy use it.
			type writerOnly struct{ io.Writer }
			remainingSize, err := io.CopyBuffer(writerOnly{file}, p, copyBuf)
			if err != nil {
				return nil, err
			}
			fh.tmpfile = file.Name()
			fh.Size = int64(b.Len()) + remainingSize
			fh.tmpoff = fileOff
			fileOff += fh.Size

			r, idxCB := newS2CompressReader(bytes.NewReader(tt.data), int64(len(tt.data)), false)
			defer r.Close()

			var rdrBuf bytes.Buffer
			_, err := io.CopyBuffer(&rdrBuf, r, buf)
			if err != nil {
				t.Fatal(err)
			}
			r.Close()
			idx := idxCB()
			if !tt.wantIdx && len(idx) > 0 {
				t.Errorf("index returned above threshold")
			}
			if tt.wantIdx {

func Copy(dst io.Writer, src io.Reader) (written int64, err error) {
	bufp := copyBufPool.Get().(*[]byte)
	buf := *bufp
	defer copyBufPool.Put(bufp)

	return io.CopyBuffer(dst, src, buf)
}

// SameFile returns if the files are same.
func SameFile(fi1, fi2 os.FileInfo) bool {
	if !os.SameFile(fi1, fi2) {
		return false
	}
	if !fi1.ModTime().Equal(fi2.ModTime()) {