ZIP64压缩扩展的兼容性问题

一、ZIP压缩的两种规范

zip64 格式是标准 zip 格式的扩展，实际上消除了 zip 存档中文件大小和数量的限制。

每种格式允许的最大值总结如下：

	Standard Format	Zip64 Format
Number of Files Inside an Archive	65,535	2^64 - 1
Size of a File Inside an Archive [bytes]	4,294,967,295	2^64 - 1
Size of an Archive [bytes]	4,294,967,295	2^64 - 1
Number of Segments in a Segmented Archive	999 (spanning) 65,535 (splitting)	4,294,967,295 - 1
Central Directory Size [bytes]	4,294,967,295	2^64 - 1

二、.NET提供的ZIP压缩能力

.NET提供了以下几个类来完成压缩功能，但是没有找到ZIP64的选项；
ZipFile
ZipArchive
ZipArchiveEntry
DeflateStream
GZipStream

三、DotNetZip提供的压缩能力

DotNetZip 是一个快速、免费的类库和工具集，用于处理 zip 文件。使用 VB、C# 或任何 .NET 语言轻松创建、提取或更新 zip 文件。

DotNetZip提供了Zip64Option来控制压缩的格式；默认情况下使用Never，即不使用ZIP64扩展；

    public enum Zip64Option
    {
        //
        // Summary:
        //     The default behavior, which is "Never". (For COM clients, this is a 0 (zero).)
        Default = 0,
        //
        // Summary:
        //     Do not use ZIP64 extensions when writing zip archives. (For COM clients, this
        //     is a 0 (zero).)
        Never = 0,
        //
        // Summary:
        //     Use ZIP64 extensions when writing zip archives, as necessary. For example, when
        //     a single entry exceeds 0xFFFFFFFF in size, or when the archive as a whole exceeds
        //     0xFFFFFFFF in size, or when there are more than 65535 entries in an archive.
        //     (For COM clients, this is a 1.)
        AsNecessary = 1,
        //
        // Summary:
        //     Always use ZIP64 extensions when writing zip archives, even when unnecessary.
        //     (For COM clients, this is a 2.)
        Always = 2
    }

我们可以通过以下方式来生成zip压缩文件

        public void ZIPContents(IDictionary<string, string> entrys, string zipFileName)
        {
            ZipFile zipfile = new ZipFile(zipFileName);
            zipfile.UseZip64WhenSaving = Zip64Option.AsNecessary;
            foreach (var entry in entrys)
            {
                zipfile.AddEntry(entry.Key, entry.Value);
            }

            zipfile.Save();
        }