Stream.CopyTo 不复制任何流数据

问题描述

我在将数据从 MemoryStream 复制到 ZipArchive 中的 Stream 时遇到问题.以下不起作用 - 它仅返回 114 个字节:

I'm having an issue with copying data from a MemoryStream into a Stream inside a ZipArchive. The following is NOT working - it returns only 114 bytes:

GetDataAsByteArray(IDataSource dataSource)
{
    using (var zipStream = new MemoryStream())
    {
        using (var archive = new ZipArchive(zipStream, ZipArchiveMode.Create, true))
        {
            var file = archive.CreateEntry("compressed.file");
            using (var targetStream = file.Open())
            {
                using (var sourceStream = new MemoryStream())
                {
                    await dataSource.LoadIntoStream(sourceStream);
                    sourceStream.CopyTo(targetStream);
                }
            }
        }
        var result = zipStream.ToArray();
        zipStream.Close();
        return result;
    }
}

但是，使用下面的复制"过程实现，所有 1103 个字节都写入数组/内存流:

However, using the implementation below for the "copy"-process, all 1103 bytes are written to the array/memory stream:

await targetStream.WriteAsync(sourceStream.ToArray(), 0, (int) sourceStream.Length);

我想知道为什么 CopyTo 产生更少的字节.此外，我对在第二个实现中转换为 Int32 感到不安全.

I'm wondering why the CopyTo yields less bytes. Also I'm feeling unsecure with the cast to Int32 in the second implementation.

仅供参考: 比较字节数组:看起来第一个实现只编写了 zip 文件的页眉和页脚.

FYI: Comparing the byte array: It looks like only the header and footer of the zip file were written by the first implementation.

推荐答案

Stream.CopyTo() 从流的当前位置开始复制.在 LoadIntoStream() 调用之后，它可能不是 0.由于它是一个 MemoryStream，你可以简单地像这样修复它:

Stream.CopyTo() starts copying from the stream's current Position. Which probably isn't 0 after that LoadIntoStream() call. Since it is a MemoryStream, you can simply fix it like this:

    await dataSource.LoadIntoStream(sourceStream);
    sourceStream.Position = 0;
    sourceStream.CopyTo(targetStream);