Web API Controller将MemoryStream转换为StreamContent

Question

我有一大堆存储在安全服务器上的图像,其中一些需要在面向世界的门户上显示.门户网站的服务器位于DMZ内部,允许请求但阻止直接请求进入安全域.图像使用SOLR编目,可以通过内部(apache？)服务器下载http://intenalname/folderA/folderAB/file.jpg

在我的内部我PhotoController可以创建一个实例WebClient,给它url并得到一个MemoryStream.如果我尝试使用这个内存流来填充response.content,我会得到一个空响应(每个fiddler).如果我使用内存流写入本地文件,然后读取文件(使用FileStream和FileInfo)它"按预期"工作.

我应该能够从一个MemoryStream到StreamContent没有经过文件系统(不应该)？但怎么样？默认构造函数StreamContent(stream)接受内存流实例而没有编译器错误......但它只是'不起作用'.

HttpResponseMessage response = Request.CreateResponse();

using (WebClient webClient = new WebClient())
{
    string url = string.Format(PHOTO_GET, filePath);
    using (MemoryStream memoryStream = new MemoryStream(webClient.DownloadData(url)))
    {
        // If these lines are unremarked the stream moves 'through' the file system and works (?!)
        //memoryStream.Position = 0;
        //string tempName = @"c:\test\" + Guid.NewGuid().ToString() + ".jpg";
        //var fs = new FileStream(tempName, FileMode.OpenOrCreate);
        //stream.CopyTo(fs);
        //fs.Close();
        //FileInfo fi = new FileInfo(tempName);

        response.Headers.AcceptRanges.Add("bytes");
        response.StatusCode = HttpStatusCode.OK;
        //response.Content =  new StreamContent(fi.ReadStream());
        response.Content = new StreamContent(memoryStream);
        response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("render");
        response.Content.Headers.ContentDisposition.FileName = fileName;
        response.Content.Headers.ContentType = new MediaTypeHeaderValue("image/jpg");//("application/octet-stream");
        response.Content.Headers.ContentLength = memoryStream.Length;

    }

}
return response;

通过Fiddler进行测试时,我得到:

[Fiddler] ReadResponse()失败:服务器没有为此请求返回完整的响应.服务器返回0个字节.

(通过FileStream时,Fiddler会向我显示图像.)

Answer 1

在您的代码中,内存流在将内容传递给响应之前就会被释放.返回的响应将使用已处理的内存流,因此无需返回,因此fiddler中的0字节.

HttpResponseMessage response = Request.CreateResponse();

using (WebClient webClient = new WebClient())
{
    string url = string.Format(PHOTO_GET, filePath);
    var memoryStream = new MemoryStream(webClient.DownloadData(url));

    response.Headers.AcceptRanges.Add("bytes");
    response.StatusCode = HttpStatusCode.OK;
    response.Content = new StreamContent(memoryStream);
    response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("render");
    response.Content.Headers.ContentDisposition.FileName = fileName;
    response.Content.Headers.ContentType = new MediaTypeHeaderValue("image/jpg");
    response.Content.Headers.ContentLength = memoryStream.Length;            
}
return response;