c# - IEnumerable 流

Question

我想做一些与下面的代码示例大致相同的事情。我想生成并提供数据流，而不必在任何时候将整个数据集都存储在内存中。

似乎我需要一些接受 IEnumerable<string> 的 Stream 实现(或 IEnumerable<byte> )在其构造函数中。在内部，此 Stream 只会在读取 Stream 或需要时遍历 IEnumerable。但我不知道有这样的 Stream 实现。

我走在正确的轨道上吗？你知道有什么方法可以做这样的事情吗？

    public FileStreamResult GetResult()
    {
        IEnumerable<string> data = GetDataForStream();

        Stream dataStream = ToStringStream(Encoding.UTF8, data);

        return File(dataStream, "text/plain", "Result");
    }

    private IEnumerable<string> GetDataForStream()
    {
        StringBuilder sb;
        for (int i = 0; i < 10000; i++)
        {
            yield return i.ToString();
            yield return "\r\n";
        }
    }

    private Stream ToStringStream(Encoding encoding, IEnumerable<string> data)
    {
        // I have to write my own implementation of stream?
        throw new NotImplementedException();
    }

Answer 1

这是一个只读的 Stream使用 IEnumerable<byte> 的实现作为输入:

public class ByteStream : Stream, IDisposable
{
    private readonly IEnumerator<byte> _input;
    private bool _disposed;

    public ByteStream(IEnumerable<byte> input)
    {
        _input = input.GetEnumerator();
    }

    public override bool CanRead => true;
    public override bool CanSeek => false;
    public override bool CanWrite => false;
    public override long Length => 0;
    public override long Position { get; set; } = 0;

    public override int Read(byte[] buffer, int offset, int count)
    {
        int i = 0;
        for (; i < count && _input.MoveNext(); i++)
            buffer[i + offset] = _input.Current;
        return i;
    }

    public override long Seek(long offset, SeekOrigin origin) => throw new InvalidOperationException();
    public override void SetLength(long value) => throw new InvalidOperationException();
    public override void Write(byte[] buffer, int offset, int count) => throw new InvalidOperationException();
    public override void Flush() => throw new InvalidOperationException();

    void IDisposable.Dispose()
    {
        if (_disposed)
            return;
        _input.Dispose();
        _disposed=  true;
    }
}

然后您仍然需要一个函数来转换 IEnumerable<string>至 IEnumerable<byte> :

public static IEnumerable<byte> Encode(IEnumerable<string> input, Encoding encoding)
{
    byte[] newLine = encoding.GetBytes(Environment.NewLine);
    foreach (string line in input)
    {
        byte[] bytes = encoding.GetBytes(line);
        foreach (byte b in bytes)
            yield return b;
        foreach (byte b in newLine)
            yield return b;
    }
}

最后，这里是如何在你的 Controller 中使用它:

public FileResult GetResult()
{
    IEnumerable<string> data = GetDataForStream();
    var stream = new ByteStream(Encode(data, Encoding.UTF8));
    return File(stream, "text/plain", "Result.txt");
}