如何使用 Web API 返回文件？

Question

我正在使用 ASP.NET Web API。
我想从 API（API 生成）下载带有 C# 的 PDF。

我可以让 API 返回一个 byte[] 吗？对于 C# 应用程序，我可以这样做：

byte[] pdf = client.DownloadData("urlToAPI");? 

和

File.WriteAllBytes()?

Answer 1

最好返回带有 StreamContent 的 HttpResponseMessage。

示例如下：

public HttpResponseMessage GetFile(string id)
{
    if (String.IsNullOrEmpty(id))
        return Request.CreateResponse(HttpStatusCode.BadRequest);

    string fileName;
    string localFilePath;
    int fileSize;

    localFilePath = getFileFromID(id, out fileName, out fileSize);

    HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.OK);
    response.Content = new StreamContent(new FileStream(localFilePath, FileMode.Open, FileAccess.Read));
    response.Content.Headers.ContentDisposition = new System.Net.Http.Headers.ContentDispositionHeaderValue("attachment");
    response.Content.Headers.ContentDisposition.FileName = fileName;
    response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");

    return response;
}

UPD来自patridge的评论： 如果其他人来到这里希望从字节数组而不是实际文件发送响应，您将需要使用 new ByteArrayContent(someData) 而不是 StreamContent（请参阅here）。

Answer 2

我做了以下动作：

[HttpGet]
[Route("api/DownloadPdfFile/{id}")]
public HttpResponseMessage DownloadPdfFile(long id)
{
    HttpResponseMessage result = null;
    try
    {
        SQL.File file = db.Files.Where(b => b.ID == id).SingleOrDefault();

        if (file == null)
        {
            result = Request.CreateResponse(HttpStatusCode.Gone);
        }
        else
        {
            // sendo file to client
            byte[] bytes = Convert.FromBase64String(file.pdfBase64);


            result = Request.CreateResponse(HttpStatusCode.OK);
            result.Content = new ByteArrayContent(bytes);
            result.Content.Headers.ContentDisposition = new System.Net.Http.Headers.ContentDispositionHeaderValue("attachment");
            result.Content.Headers.ContentDisposition.FileName = file.name + ".pdf";
        }

        return result;
    }
    catch (Exception ex)
    {
        return Request.CreateResponse(HttpStatusCode.Gone);
    }
}

Answer 3

请注意.Net Core：如果我们想发送原始字节，我们可以使用FileContentResult 并将contentType 设置为application/octet-stream。示例：

[HttpGet("{id}")]
public IActionResult GetDocumentBytes(int id)
{
    byte[] byteArray = GetDocumentByteArray(id);
    return new FileContentResult(byteArray, "application/octet-stream");
}

Answer 4

ApiController 中的IHttpActionResult 示例。

[HttpGet]
[Route("file/{id}/")]
public IHttpActionResult GetFileForCustomer(int id)
{
    if (id == 0)
      return BadRequest();

    var file = GetFile(id);

    IHttpActionResult response;
    HttpResponseMessage responseMsg = new HttpResponseMessage(HttpStatusCode.OK);
    responseMsg.Content = new ByteArrayContent(file.SomeData);
    responseMsg.Content.Headers.ContentDisposition = new System.Net.Http.Headers.ContentDispositionHeaderValue("attachment");
    responseMsg.Content.Headers.ContentDisposition.FileName = file.FileName;
    responseMsg.Content.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
    response = ResponseMessage(responseMsg);
    return response;
}

如果您不想下载 PDF 并使用内置 PDF 查看器的浏览器，请删除以下两行：

responseMsg.Content.Headers.ContentDisposition = new System.Net.Http.Headers.ContentDispositionHeaderValue("attachment");
responseMsg.Content.Headers.ContentDisposition.FileName = file.FileName;

Answer 5

我一直想知道是否有一种简单的方法可以以更...“通用”的方式下载文件。我想出了这个。

这是一个简单的ActionResult，允许您从返回IHttpActionResult 的控制器调用下载文件。 该文件存储在byte[] Content 中。如果需要，您可以将其转换为流。

我用它来返回存储在数据库的 varbinary 列中的文件。

    public class FileHttpActionResult : IHttpActionResult
    {
        public HttpRequestMessage Request { get; set; }

        public string FileName { get; set; }
        public string MediaType { get; set; }
        public HttpStatusCode StatusCode { get; set; }

        public byte[] Content { get; set; }

        public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
        {
            HttpResponseMessage response = new HttpResponseMessage(StatusCode);

            response.StatusCode = StatusCode;
            response.Content = new StreamContent(new MemoryStream(Content));
            response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment");
            response.Content.Headers.ContentDisposition.FileName = FileName;
            response.Content.Headers.ContentType = new MediaTypeHeaderValue(MediaType);

            return Task.FromResult(response);
        }
    }

Answer 6

你可以试试，HttpClient 从另一端下载文件，同时你可以作为文件结果传递

 [HttpGet]
    [Route("api/getFile")]
    public async  Task<FileResult> GetFile(string Param1,string Param2)
    {
        try
        {
            Stream stream = null;
            string strURL = @"File URL";
            HttpClient client = new HttpClient();
            HttpResponseMessage httpResponse = await client.GetAsync(strURL);
            Stream streamToReadFrom = await httpResponse.Content.ReadAsStreamAsync();
            return File(streamToReadFrom, "{MIME TYPE}");

        }
        catch (Exception ex)
        {

            throw ex;
        }
        finally
        { 
        
        }
    }

Answer 7

另一种下载文件的方法是将流内容直接写入响应的正文：

[HttpGet("pdfstream/{id}")]
public async Task  GetFile(long id)
{        
    var stream = GetStream(id);
    Response.StatusCode = (int)HttpStatusCode.OK;
    Response.Headers.Add( HeaderNames.ContentDisposition, $"attachment; filename=\"{Guid.NewGuid()}.pdf\"" );
    Response.Headers.Add( HeaderNames.ContentType, "application/pdf"  );            
    await stream.CopyToAsync(Response.Body);
    await Response.Body.FlushAsync();           
}