ASP.NET核心禁用响应缓冲

问题描述

我正在尝试将一个动态构建的大型JSON文件传输到客户端(可能超过500MB)。我尝试禁用响应缓冲的原因有很多，但主要是为了提高内存效率。

我尝试直接写入HttpContext.Response.BodyWriter，但响应似乎在写入输出之前缓冲在内存中。此方法的返回类型为Task。

HttpContext.Response.ContentType = "application/json";
HttpContext.Response.ContentLength = null;
await HttpContext.Response.StartAsync(cancellationToken);
var bodyStream = HttpContext.Response.BodyWriter.AsStream(true);
await bodyStream.WriteAsync(Encoding.UTF8.GetBytes("["), cancellationToken);
await foreach (var item in cursor.WithCancellation(cancellationToken)
    .ConfigureAwait(false))
{
    await bodyStream.WriteAsync(JsonSerializer.SerializeToUtf8Bytes(item, DefaultSettings.JsonSerializerOptions), cancellationToken);
    await bodyStream.WriteAsync(Encoding.UTF8.GetBytes(","), cancellationToken);
    
    await bodyStream.FlushAsync(cancellationToken);
    await Task.Delay(100,cancellationToken);
}
await bodyStream.WriteAsync(Encoding.UTF8.GetBytes("]"), cancellationToken);
bodyStream.Close();
await HttpContext.Response.CompleteAsync().ConfigureAwait(false);

注意：我意识到此代码非常繁琐，试图使其正常工作，然后将其清除

我已尝试

更新

var responseBufferingFeature = context.Features.Get<IHttpResponseBodyFeature>();
responseBufferingFeature?.DisableBuffering();

已更新示例代码

这非常简单地再现了这个问题。在调用response.CompleteAsync()之前，客户端不会收到任何数据。

[HttpGet]
[Route("stream")]
public async Task<EmptyResult> FileStream(CancellationToken cancellationToken)
{
    var response = DisableResponseBuffering(HttpContext);
    HttpContext.Response.Headers.Add("Content-Type", "application/gzip");
    HttpContext.Response.Headers.Add("Content-Disposition", $"attachment; filename="player-data.csv.gz"");
    await response.StartAsync().ConfigureAwait(false);
    var memory = response.Writer.GetMemory(1024*1024*10);
    response.Writer.Advance(1024*1024*10);
    await response.Writer.FlushAsync(cancellationToken).ConfigureAwait(false);
    await Task.Delay(5000).ConfigureAwait(false);
    var str2 = Encoding.UTF8.GetBytes("Bar!
");
    memory = response.Writer.GetMemory(str2.Length);
    str2.CopyTo(memory);
    response.Writer.Advance(str2.Length);
    await response.CompleteAsync().ConfigureAwait(false);
    return new EmptyResult();
}

private IHttpResponseBodyFeature DisableResponseBuffering(HttpContext context)
{
    var responseBufferingFeature = context.Features.Get<IHttpResponseBodyFeature>();
    responseBufferingFeature?.DisableBuffering();
    return responseBufferingFeature;
}

推荐答案

对于仍感兴趣的用户，此代码在使用cURL时立即发送数据：

public async Task Invoke(HttpContext context)
{
    var g = context.Features.Get<IHttpResponseBodyFeature>();
    g.DisableBuffering(); // doesn't seem to make a difference

    context.Response.StatusCode = 200;
    context.Response.ContentType = "text/plain; charset=utf-8";
    //context.Response.ContentLength = null;

    await g.StartAsync();

    for (int i = 0; i < 10; ++i)
    {
        var line = $"this is line {i}
";
        var bytes = utf8.GetBytes(line);
        // it seems context.Response.Body.WriteAsync() and
        // context.Response.BodyWriter.WriteAsync() work exactly the same
        await g.Writer.WriteAsync(new ReadOnlyMemory<byte>(bytes));
        await g.Writer.FlushAsync();
        await Task.Delay(1000);
    }

    await g.CompleteAsync();
}

我尝试使用和不使用DisableBufering()以及写入管道(IHttpResponseBodyFeature.WritervsHttpContext.Response.Body)的变化似乎没有什么不同。

在cURL中，它会立即显示消息，但在Chrome和一些REST客户端中，它会等待整个流显示。

因此，我建议使用不等待整个流呈现代码的客户端来测试代码行为。我仍在检查的另一个选项是，如果客户端请求压缩，即使管道中没有配置压缩，aspnet core是否会自动获取压缩可能性。 所以我建议