Method ensureCache

internal/stream/stream.go:198–224

*旧笔记 使用bytes.Buffer作为io.CopyBuffer的写入对象，CopyBuffer会调用Buffer.ReadFrom 即使被写入的数据量与Buffer.Cap一致，Buffer也会扩大 确保指定大小的数据被缓存

(size int64)

// 确保指定大小的数据被缓存
func (f *FileStream) ensureCache(size int64) (model.File, error) {
	if f.peek == nil {
		blockSize := min(size, f.GetSize(), int64(conf.MaxBlockLimit))
		var err error
		f.hc, err = hcache.NewHybridCache(uint64(blockSize), uint64(f.GetSize()))
		if err != nil {
			return nil, err
		}
		f.peek = buffer.NewDynamicReadAtSeeker(f.hc)
		f.oriReader = f.Reader
		f.Reader = io.MultiReader(f.peek, f.oriReader)
		f.Add(f.hc)
	}
	size = size - f.peek.Size()
	if size <= 0 {
		return f.peek, nil
	}
	written, err := f.hc.CopyFromN(f.oriReader, size)
	if written != size {
		f.hc.RewindBySize(uint64(size - written))
		return nil, fmt.Errorf("failed to read all data: (expect =%d, actual =%d) %w", size, written, err)
	}
	if f.peek.Size() >= f.GetSize() {
		f.Reader = f.peek
	}
	return f.peek, nil
}

var _ model.FileStreamer = (*SeekableStream)(nil)
var _ model.FileStreamer = (*FileStream)(nil)