使用HttpClient.GetStreamAsync加载StreamContent报错，File.OpenRead正常

我需要在两个Web服务之间传输PDF文件。最初通过await httpClient.GetStreamAsync(varPdfUrl)将文件下载到本地存储，再用File.OpenRead()读取流上传到目标服务（这部分代码已注释），但尝试直接用await httpClient.GetStreamAsync(varPdfUrl)生成StreamContent时，出现以下错误：

错误信息：

System.Net.Http.HttpRequestException: 复制内容到流时出错。
---> System.IO.IOException: 无法将数据写入传输连接：远程主机强迫关闭了一个现有的连接。

原始代码 #

var httpClient = new HttpClient();
var request = new HttpRequestMessage(HttpMethod.Post, uploadResponse.url);
var content = new MultipartFormDataContent();

// 填充MultipartFormDataContent 
content.Add(new StringContent(uploadResponse.fields.key), "key");
content.Add(new StringContent(uploadResponse.fields.ContentType), "Content-Type");

// 添加文件流
string fileName = drawingTemp.ProjectNumber + "-" + drawingTemp.Title + ".pdf";

//string localPath = @"C:\... \CMP\Drawing Downloads\";
//var fileSteamLocalFile = new StreamContent(File.OpenRead(localPath + fileName));
//content.Add(fileSteamLocalFile, "file", fileName);

var fileSteam = new StreamContent(await httpClient.GetStreamAsync(drawingTemp.PdfUrl));
content.Add(fileSteam, "file", fileName );

content.Add(new StringContent(uploadResponse.uuid), "uuid");

try
{
    //上传文件到AWS
    request.Content = content;
    var responseUploadFileMsg = await httpClient.SendAsync(request);
}

临时解决方案 #

目前通过将文件先写入项目文件夹wwwroot/Files，再用File.OpenRead()读取生成StreamContent的方式成功上传，但仍想了解直接用HttpClient.GetStreamAsync()生成StreamContent报错的原因。

对应代码：

var httpClient = new HttpClient();
var request = new HttpRequestMessage(HttpMethod.Post, uploadResponse.url);
var content = new MultipartFormDataContent();

// 添加文件流
string fileName = drawingTemp.ProjectNumber + "-" + drawingTemp.Title + ".pdf";
Stream fileSteam = await httpClient.GetStreamAsync(drawingTemp.PdfUrl);

// 将流转换为文件并临时保存到wwwroot/Files 
string writeFullPath = @"wwwroot\Files\" + fileName;

if (!File.Exists(writeFullPath))
{
    using var fileLocalPath = File.Create(writeFullPath);
    {
        fileSteam.CopyTo(fileLocalPath);
        fileSteam.Dispose();
    }
}

string readFullPath = Environment.CurrentDirectory + @"\wwwroot\Files\" + fileName;

// 将文件流添加到内容中
var fileSteamLocalFile = new StreamContent(File.OpenRead(readFullPath));
content.Add(fileSteamLocalFile, "file", fileName);

content.Add(new StringContent(uploadResponse.uuid), "uuid");

try
{
    //上传文件到AWS
    request.Content = content;
    var responseUploadFileMsg = await httpClient.SendAsync(request);
    fileSteamLocalFile.Dispose();

    // 删除临时文件 
    if (File.Exists(readFullPath))
    {
        File.Delete(readFullPath);
    }
}

内容的提问来源于stack exchange，提问作者Todd T