复制除流的最后16个字节以外的所有字节？早期检测到流末？

Question

这与C#有关.我们有一种情况需要将整个源流复制到目标流中,除了最后16个字节.

编辑:流可以达到40GB,所以不能做一些静态byte []分配(例如:.ToArray())

看看MSDN文档,似乎只有当返回值为0时我们才能可靠地确定流的结束.返回值介于0和之间the requested size可能意味着字节"当前不可用"(这究竟意味着什么？)

目前,它按如下方式复制每个字节.inStream并且outStream是通用的 - 可以是内存,磁盘或网络流(实际上也是一些).

public static void StreamCopy(Stream inStream, Stream outStream)
{
    var buffer = new byte[8*1024];
    var last16Bytes = new byte[16];
    int bytesRead;
    while ((bytesRead = inStream.Read(buffer, 0, buffer.Length)) > 0)
    {
        outStream.Write(buffer, 0, bytesRead);
    }
    // Issues:
    // 1. We already wrote the last 16 bytes into 
    //    outStream (possibly over the n/w)
    // 2. last16Bytes = ? (inStream may not necessarily support rewinding)
}

什么是可靠的方法来确保复制除了最后16个之外的所有内容？我能想到的使用Position和Length对进入数据流,但有一个疑难杂症MSDN,说

如果从Stream派生的类不支持搜索,则调用Length,SetLength,Position和Seek会抛出NotSupportedException..

Answer 1

1. Read between 1 and n bytes from the input stream.¹

2. Append the bytes to a circular buffer.²

3. Write the first max(0, b - 16) bytes from the circular buffer to the output stream, where b is the number of bytes in the circular buffer.

4. Remove the bytes that you just have written from the circular buffer.

5. Go to step 1.

¹This is what the Read method does – if you call int n = Read(buffer, 0, 500); it will read between 1 and 500 bytes into buffer and return the number of bytes read. If Read returns 0, you have reached the end of the stream.

²For maximum performance, you can read the bytes directly from the input stream into the circular buffer. This is a bit tricky, because you have to deal with the wraparound within the array underlying the buffer.