寻求C# CopyToAsync源码链接及ASP.NET Core 6流释放问题解答

一、需求：获取指定CopyToAsync方法的源码 #

需要获取C#中以下签名的CopyToAsync方法源码：

public System.Threading.Tasks.Task CopyToAsync (System.IO.Stream destination, System.Threading.CancellationToken cancellationToken);

二、问题场景与代码 #

在ASP.NET Core 6.0中实现Excel文件下载功能时遇到问题，相关代码如下：

namespace Magicodes.ExporterAndImporter.Excel.AspNetCore
{
    /// <summary>
    /// 基类
    /// </summary>
    public class XlsxFileResultBase : ActionResult
    {
        /// <summary>
        /// 下载Excel文件
        /// </summary>
        /// <param name="context"></param>
        /// <param name="stream"></param>
        /// <param name="downloadFileName"></param>
        /// <returns></returns>
        protected virtual async Task DownloadExcelFileAsync(ActionContext context,
                                                            Stream stream,
                                                            string downloadFileName)
        {
            var response = context.HttpContext.Response;
            response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";

            if (downloadFileName == null)
            {
                downloadFileName = Guid.NewGuid().ToString("N") + ".xlsx";
            }

            if (string.IsNullOrEmpty(Path.GetExtension(downloadFileName)))
            {
                downloadFileName += ".xlsx";
            }

            context.HttpContext.Response.Headers.Add("Content-Disposition", new[] {
                "attachment; filename=" + HttpUtility.UrlEncode(downloadFileName)
            });
            await stream.CopyToAsync(context.HttpContext.Response.Body);
        }
    }
}

此前使用using声明MemoryStream时，触发了如下错误：

错误消息: Cannot access a closed Stream.
堆栈信息: at System.IO.MemoryStream.CopyToAsync(Stream destination, Int32 bufferSize, CancellationToken cancellationToken)

三、疑问 #

不清楚传入上述方法的Stream是否需要手动释放，想确认在ASP.NET Core 6.0返回文件流的场景下，该Stream是否会被自动释放，希望以源码作为依据。

内容的提问来源于stack exchange，提问作者Sheldon_XiTong