这个问题帮助了我。

所以，试试这个:

控制器代码:

[HttpGet]
public HttpResponseMessage Test()
{
    var path = System.Web.HttpContext.Current.Server.MapPath("~/Content/test.docx");;
    HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK);
    var stream = new FileStream(path, FileMode.Open);
    result.Content = new StreamContent(stream);
    result.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment");
    result.Content.Headers.ContentDisposition.FileName = Path.GetFileName(path);
    result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
    result.Content.Headers.ContentLength = stream.Length;
    return result;          
}

查看Html标记(点击事件和简单的url):

<script type="text/javascript">
    $(document).ready(function () {
        $("#btn").click(function () {
            // httproute = "" - using this to construct proper web api links.
            window.location.href = "@Url.Action("GetFile", "Data", new { httproute = "" })";
        });
    });
</script>


<button id="btn">
    Button text
</button>

<a href=" @Url.Action("GetFile", "Data", new { httproute = "" }) ">Data</a>

而不是返回StreamContent作为内容，我可以使它与ByteArrayContent一起工作。

[HttpGet]
public HttpResponseMessage Generate()
{
    var stream = new MemoryStream();
    // processing the stream.

    var result = new HttpResponseMessage(HttpStatusCode.OK)
    {
        Content = new ByteArrayContent(stream.ToArray())
    };
    result.Content.Headers.ContentDisposition =
        new System.Net.Http.Headers.ContentDispositionHeaderValue("attachment")
    {
        FileName = "CertificationCard.pdf"
    };
    result.Content.Headers.ContentType =
        new MediaTypeHeaderValue("application/octet-stream");

    return result;
}

我不太确定是哪一部分的问题，但这就是为什么MemoryStream不适合你:

当你写入MemoryStream时，它会增加它的Position属性。 StreamContent的构造函数会考虑流的当前位置。因此，如果您写入流，然后将其传递给StreamContent，响应将从流末尾的虚无开始。

有两种方法可以正确解决这个问题:

construct content, write to stream [HttpGet] public HttpResponseMessage Test() { var stream = new MemoryStream(); var response = Request.CreateResponse(HttpStatusCode.OK); response.Content = new StreamContent(stream); // ... // stream.Write(...); // ... return response; } write to stream, reset position, construct content [HttpGet] public HttpResponseMessage Test() { var stream = new MemoryStream(); // ... // stream.Write(...); // ... stream.Position = 0; var response = Request.CreateResponse(HttpStatusCode.OK); response.Content = new StreamContent(stream); return response; } looks a little better if you have a fresh Stream, 1) is simpler if your stream does not start at 0

如果你想返回IHttpActionResult，你可以这样做:

[HttpGet]
public IHttpActionResult Test()
{
    var stream = new MemoryStream();

    var result = new HttpResponseMessage(HttpStatusCode.OK)
    {
        Content = new ByteArrayContent(stream.GetBuffer())
    };
    result.Content.Headers.ContentDisposition = new System.Net.Http.Headers.ContentDispositionHeaderValue("attachment")
    {
        FileName = "test.pdf"
    };
    result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");

    var response = ResponseMessage(result);

    return response;
}

对我来说，这就是

var response = Request.CreateResponse(HttpStatusCode.OK, new StringContent(log, System.Text.Encoding.UTF8, "application/octet-stream");

and

var response = Request.CreateResponse(HttpStatusCode.OK);
response.Content = new StringContent(log, System.Text.Encoding.UTF8, "application/octet-stream");

第一个是返回StringContent的JSON表示形式:{"Headers":[{"Key":"Content-Type"，"Value":["application/octet-stream;charset = utf - 8”]}]}

而第二个则是正常返回文件。

似乎请求。CreateResponse有一个重载，它将字符串作为第二个参数，这似乎是导致StringContent对象本身呈现为字符串而不是实际内容的原因。

这里是一个不缓冲文件内容的流输出实现(如果它是一个大文件，缓冲在byte[] / MemoryStream等中可能是一个服务器问题)。

public class FileResult : IHttpActionResult
{
    public FileResult(string filePath)
    {
        if (filePath == null)
            throw new ArgumentNullException(nameof(filePath));

        FilePath = filePath;
    }

    public string FilePath { get; }

    public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
    {
        var response = new HttpResponseMessage(HttpStatusCode.OK);
        response.Content = new StreamContent(File.OpenRead(FilePath));
        var contentType = MimeMapping.GetMimeMapping(Path.GetExtension(FilePath));
        response.Content.Headers.ContentType = new MediaTypeHeaderValue(contentType);
        return Task.FromResult(response);
    }
}

它可以这样简单地使用:

public class MyController : ApiController
{
    public IHttpActionResult Get()
    {
        string filePath = GetSomeValidFilePath();
        return new FileResult(filePath);
    }
}

 var memoryStream = new MemoryStream();
                await cloudFile.DownloadToStreamAsync(memoryStream);
                responseMessage.result = "Success";

                var contentType = "application/octet-stream";
            
                **using (var stream = new MemoryStream())
                {                    
                    return File(memoryStream.GetBuffer(), contentType, "Cartage.pdf");
                }**

我发现这篇文章很有用:https://codeburst.io/download-files-using-web-api-ae1d1025f0a9

基本上它说:

[Route("api/[controller]")]
[ApiController]
public class JobController : ControllerBase
{
    [HttpGet]
    public ActionResult GetFile()
    {
        byte[] fileContent = GetFile();
        return File(fileContent, "application/pdf", "test.pdf");
    }
}