StreamContent 没有加载到最后

Question

我有（几个）WebAPI 操作，它们从数据库（通过 EF）加载 QuickFix 日志，并使用此私有方法将它们 return 作为 CSV：

private HttpResponseMessage BuildCsvResponse<T>(T[] entries, Func<T, string> row, string fileName)
{
    var response = new HttpResponseMessage(HttpStatusCode.OK);
    var stream = new MemoryStream();
    var writer = new StreamWriter(stream);
    var i = entries.Length;
    foreach (var entry in entries)
    {
        i--;
        writer.WriteLine(row(entry)); // simply call to overridden ToString() method
    }
    stream.Seek(0, SeekOrigin.Begin);
    stream.Flush();
    response.Content = new StreamContent(stream);
    response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
    {
        FileName = fileName,
    };
    response.Content.Headers.ContentType = new MediaTypeHeaderValue("text/csv");
    return response;
}

问题是内容永远不会加载到末尾并在离末尾不远的随机符号上剪切。为什么会发生？

可能这很重要 - 所有日志字符串都包含分隔符 0x01

Answer 1

在接触底层流之前，您需要刷新流编写器的内部缓冲区。

最好是使用另一个 contructor 告诉您的 StreamWriter 保持流打开。然后，您可以安全地处置您的 streamwriter，使其刷新其缓冲区，同时您的 memorystream 实例保持打开状态并且不会被处置。

请注意，您需要选择与您的 HTTP 内容响应相匹配的编码。我这里选择的是UTF8，相应修改。

var stream = new MemoryStream();
// notice the true as last parameter, false is the default.
using(var writer = new StreamWriter(stream, Encoding.UTF8, 8192, true))
{
    var i = entries.Length;
    foreach (var entry in entries)
    {
        i--;
        writer.WriteLine(row(entry)); // simply call to overridden ToString() method
    }
}
// your streamwriter has now flushed its buffer and left the stream open
stream.Seek(0, SeekOrigin.Begin);
// calling Flush on the stream was never needed so I removed that.
response.Content = new StreamContent(stream);

StreamContent 没有加载到最后

StreamContent not loaded to the end

c#

memorystream

asp.net-web-api