Web API: Download Multiple Files Separately

Question

I have a Web Api controller method that gets passed document IDs and it should return the document files individually for those requested Ids. I have tried the accepted answer from the following link to achieve this functionality, but it's not working. I don't know where I did go wrong.

What's the best way to serve up multiple binary files from a single WebApi method?

My Web Api Method,

   public async Task<HttpResponseMessage> DownloadMultiDocumentAsync( 
             IClaimedUser user, string documentId)
    {
        List<long> docIds = documentId.Split(',').Select(long.Parse).ToList();
        List<Document> documentList = coreDataContext.Documents.Where(d => docIds.Contains(d.DocumentId) && d.IsActive).ToList();

        var content = new MultipartContent();
        CloudBlockBlob blob = null;

        var container = GetBlobClient(tenantInfo);
        var directory = container.GetDirectoryReference(
            string.Format(DirectoryNameConfigValue, tenantInfo.TenantId.ToString(), documentList[0].ProjectId));

        for (int docId = 0; docId < documentList.Count; docId++)
        {
            blob = directory.GetBlockBlobReference(DocumentNameConfigValue + documentList[docId].DocumentId);
            if (!blob.Exists()) continue;

            MemoryStream memStream = new MemoryStream();
            await blob.DownloadToStreamAsync(memStream);
            memStream.Seek(0, SeekOrigin.Begin);
            var streamContent = new StreamContent(memStream);
            content.Add(streamContent);

        }            
        HttpResponseMessage httpResponseMessage = new HttpResponseMessage();
        httpResponseMessage.Content = content;
        httpResponseMessage.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
        httpResponseMessage.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment");
        httpResponseMessage.StatusCode = HttpStatusCode.OK;
        return httpResponseMessage;
    }

I tried with 2 or more document Ids but only one file was downloaded and that also is not in the correct format (without extension).

Answer 1

Zipping is the only option that will have consistent result on all browsers. MIME/multipart content is for email messages (https://en.wikipedia.org/wiki/MIME#Multipart_messages) and it was never intended to be received and parsed on the client side of a HTTP transaction. Some browsers do implement it, some others don't.

Alternatively, you can change your API to take in a single docId and iterate over your API from your client for each docId.

Answer 2

I think only way is that you zip your all the files and then download one zip file. I guess you can use dotnetzip package because it is easy to use.

One way is that, you can first save your files on disk and then stream the zip to download. Another way is, you can zip them in memory and then download the file in stream

public ActionResult Download()
{
    using (ZipFile zip = new ZipFile())
    {
        zip.AddDirectory(Server.MapPath("~/Directories/hello"));

        MemoryStream output = new MemoryStream();
        zip.Save(output);
        return File(output, "application/zip", "sample.zip");
    }  
}