Not able to properly download files from azure storage and data are lost too when downloading files

Question

I have 2 files saved on Azure blob storage:

Abc.txt
Pqr.docx

Now i want to create zip files of this 2 files and allow user to download.

I have saved this in my database table field like this:

Document
Abc,Pqr

Now when i click on download then i am getting file like below with no data in it and file extension are lost too like below:

I want user to get exact file(.txt,.docx) in zip when user download zip file.

This is my code:

public ActionResult DownloadImagefilesAsZip()
{
    string documentUrl = repossitory.GetDocumentsUrlbyId(id);//output:Abc.txt,Pqr.Docx
          if (!string.IsNullOrEmpty(documentUrl))
            {
                string[] str = documentUrl.Split(',');
                if (str.Length > 1)
                {
                    using (ZipFile zip = new ZipFile())
                    {
                        int cnt = 0;
                        foreach (string t in str)
                        {
                            if (!string.IsNullOrEmpty(t))
                            {
                                Stream s = this.GetFileContent(t);
                                zip.AddEntry("File" + cnt, s);

                            }
                            cnt++;
                        }
                        zip.Save(outputStream);
                        outputStream.Position = 0;
                        return File(outputStream, "application/zip", "all.zip");
                    }
                }

}

  public Stream GetFileContent(string fileName)
        {
            CloudBlobContainer container = this.GetCloudBlobContainer();
            CloudBlockBlob blockBlob = container.GetBlockBlobReference(fileName);
            var stream = new MemoryStream();
            blockBlob.DownloadToStream(stream);
            return stream;
        }

 public CloudBlobContainer GetCloudBlobContainer()
        {
            CloudStorageAccount storageAccount = CloudStorageAccount.Parse(ConfigurationManager.AppSettings["StorageConnectionString"].ToString());
            CloudBlobClient blobclient = storageAccount.CreateCloudBlobClient();
            CloudBlobContainer blobcontainer = blobclient.GetContainerReference("Mystorage");
            if (blobcontainer.CreateIfNotExists())
            {
                blobcontainer.SetPermissions(new BlobContainerPermissions { PublicAccess = BlobContainerPublicAccessType.Blob });
            }
            blobcontainer.SetPermissions(new BlobContainerPermissions { PublicAccess = BlobContainerPublicAccessType.Blob });
            return blobcontainer;
        }

I want same file to be downloaded when user download zip file.

Can anybody help me with this??

score 2 · Answer 1 · answered Oct 26 '15 at 07:14

I'm not a web dev, but hopefully this will help. This snippet of code is in a method where I download a list of blobs into a zip file archive using a stream. The list of files had the slashes in all directions, so there's code in here to fix this, and to make sure I'm getting the blob reference with the right text (no URL, and no opening slash if the blob is in a "folder").

I suspect your problem is not using a memory stream or a binary writer. Specificity helps sometimes. Good luck.

using (ZipArchive zipFile = ZipFile.Open(outputZipFileName, ZipArchiveMode.Create))
{
    foreach (string oneFile in listOfFiles)
    {
        //Need the filename, complete with relative path. Make it like a file name on disk, with backwards slashes.
        //Also must be relative, so can't start with a slash. Remove if found.
        string filenameInArchive = oneFile.Replace(@"/", @"\");
        if (filenameInArchive.Substring(0, 1) == @"\")
            filenameInArchive = filenameInArchive.Substring(1, filenameInArchive.Length - 1);

        //blob needs slashes in opposite direction
        string blobFile = oneFile.Replace(@"\", @"/");

        //take first slash off of the (folder + file name) to access it directly in blob storage
        if (blobFile.Substring(0, 1) == @"/")
            blobFile = oneFile.Substring(1, oneFile.Length - 1);

        var cloudBlockBlob = this.BlobStorageSource.GetBlobRef(blobFile);
        if (!cloudBlockBlob.Exists()) //checking just in case
        {
            //go to the next file
            //should probably trace log this 
            //add the file name with the fixed slashes rather than the raw, messed-up one
            //  so anyone looking at the list of files not found doesn't think it's because
            //  the slashes are different
            filesNotFound.Add(blobFile);
        }
        else
        {
            //blob listing has files with forward slashes; that's what the zip file requires
            //also, first character should not be a slash (removed it above)

            ZipArchiveEntry newEntry = zipFile.CreateEntry(filenameInArchive, CompressionLevel.Optimal);

            using (MemoryStream ms = new MemoryStream())
            {
                //download the blob to a memory stream
                cloudBlockBlob.DownloadToStream(ms);

                //write to the newEntry using a BinaryWriter and copying it 4k at a time
                using (BinaryWriter entry = new BinaryWriter(newEntry.Open()))
                {
                    //reset the memory stream's position to 0 and copy it to the zip stream in 4k chunks
                    //this keeps the process from taking up a ton of memory
                    ms.Position = 0;
                    byte[] buffer = new byte[4096];

                    bool copying = true;
                    while (copying)
                    {
                        int bytesRead = ms.Read(buffer, 0, buffer.Length);
                        if (bytesRead > 0)
                        {
                            entry.Write(buffer, 0, bytesRead);
                        }
                        else
                        {
                            entry.Flush();
                            copying = false;
                        }
                    }
                }//end using for BinaryWriter

            }//end using for MemoryStream

        }//if file exists in blob storage

    }//end foreach file

} //end of using ZipFileArchive

can you please tell me how do i integrate this with my mvc controller method because main problem is with my controller like how would be my controller method? — I Love Stackoverflow, Oct 26 '15 at 08:45

score 1 · Answer 2 · edited May 23 '17 at 11:59

I have seen people using ICSharpZip library, take a look at this piece of code

public void ZipFilesToResponse(HttpResponseBase response, IEnumerable<Asset> files, string zipFileName)
    {
        using (var zipOutputStream = new ZipOutputStream(response.OutputStream))
        {
            zipOutputStream.SetLevel(0); // 0 - store only to 9 - means best compression
            response.BufferOutput = false;
            response.AddHeader("Content-Disposition", "attachment; filename=" + zipFileName);
            response.ContentType = "application/octet-stream";

            foreach (var file in files)
            {
                var entry = new ZipEntry(file.FilenameSlug())
                {
                    DateTime = DateTime.Now,
                    Size = file.Filesize
                };
                zipOutputStream.PutNextEntry(entry);
                storageService.ReadToStream(file, zipOutputStream);
                response.Flush();
                if (!response.IsClientConnected)
                {
                   break;
                }
            }
            zipOutputStream.Finish();
            zipOutputStream.Close();
        }
        response.End();
    }

Taken from here generate a Zip file from azure blob storage files

Sorry i cant use another Zip dll and most importantly how would i return it from my mvc controller?? — I Love Stackoverflow, Oct 26 '15 at 06:19

Gaurav Mantri · Accepted Answer · 2015-10-28T07:07:31.740

1

There are two things I noticed:

Once you read the blob contents in stream, you are not resetting that stream's position to 0. Thus all files in your zip are of zero bytes.
When calling AddEntry, you may want to specify the name of the blob there instead of "File"+cnt.

Please look at the code below. It's a console app that creates the zip file and writes it on the local file system.

    static void SaveBlobsToZip()
    {
        string[] str = new string[] { "CodePlex.png", "DocumentDB.png" };
        var account = new CloudStorageAccount(new StorageCredentials(accountName, accountKey), true);
        var blobClient = account.CreateCloudBlobClient();
        var container = blobClient.GetContainerReference("images");
        using (var fs = new FileStream("D:\\output.zip", FileMode.Create))
        {
            fs.Position = 0;
            using (var ms1 = new MemoryStream())
            {
                using (ZipFile zip = new ZipFile())
                {
                    int cnt = 0;
                    foreach (string t in str)
                    {
                        var ms = new MemoryStream();
                        container.GetBlockBlobReference(t).DownloadToStream(ms);
                        ms.Position = 0;//This was missing from your code
                        zip.AddEntry(t, ms);//You may want to give the name of the blob here.
                        cnt++;
                    }
                    zip.Save(ms1);
                }
                ms1.Position = 0;
                ms1.CopyTo(fs);
            }
        }
    }

UPDATE

Here's the code in the MVC application (though I am not sure it is the best code :) but it works). I modified your code a little bit.

    public ActionResult DownloadImagefilesAsZip()
    {
        string[] str = new string[] { "CodePlex.png", "DocumentDB.png" }; //repossitory.GetDocumentsUrlbyId(id);//output:Abc.txt,Pqr.Docx
        CloudBlobContainer blobcontainer = GetCloudBlobContainer();// azureStorageUtility.GetCloudBlobContainer();
        MemoryStream ms1 = new MemoryStream();
        using (ZipFile zip = new ZipFile())
        {
            int cnt = 0;
            foreach (string t in str)
            {
                var ms = new MemoryStream();
                CloudBlockBlob blockBlob = blobcontainer.GetBlockBlobReference(t);
                blockBlob.DownloadToStream(ms);
                ms.Position = 0;//This was missing from your code
                zip.AddEntry(t, ms);//You may want to give the name of the blob here.
                cnt++;
            }
            zip.Save(ms1);
        }
        ms1.Position = 0;
        return File(ms1, "application/zip", "all.zip");
    }

edited Oct 28 '15 at 07:07

answered Oct 26 '15 at 07:47

Gaurav Mantri

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Thank you so much gaurav.Now can you please tell me that how return this zip file from my controller method because i am badly stuck in that only. – I Love Stackoverflow Oct 26 '15 at 08:47
1

I think that the code you have should work - `return File(outputStream, "application/zip", "all.zip");`. Are you getting an error there? – Gaurav Mantri Oct 26 '15 at 08:51
Is it necessary to do this D:\\output.zip ? – I Love Stackoverflow Oct 28 '15 at 05:42
1

Oh no .... since I made a console app, I wanted to write the zip file to desktop to see if the file is written properly. Instead of FileStream, you can write the contents of zip file to a memory stream, reset it's position to zero and then return that as File (what you're doing in your code). HTH. – Gaurav Mantri Oct 28 '15 at 05:50
return File(outputStream, "application/zip", "all.zip");Getting error on "outputStream" – I Love Stackoverflow Oct 28 '15 at 05:52
outputStream does not exist in the current context – I Love Stackoverflow Oct 28 '15 at 05:58
Can you share your current code? You can put that on pastebin.com and share the link here. I am sure there's some minor issue here or there :) – Gaurav Mantri Oct 28 '15 at 06:01
I think return File(ms1, "application/zip", "all.zip") should come? – I Love Stackoverflow Oct 28 '15 at 06:01
i am creating pastebin for you.will share a link – I Love Stackoverflow Oct 28 '15 at 06:04
Thanks. Let me get back to you in a bit. – Gaurav Mantri Oct 28 '15 at 06:09
Yeah sure sir.Thank you for all this.sorry thank you wont be enough to actually thank you – I Love Stackoverflow Oct 28 '15 at 06:10
with this line: return File(ms1, "application/zip", "all.zip");I am getting this error:Cannot access a closed Stream. – I Love Stackoverflow Oct 28 '15 at 06:16
Updated my answer. HTH. – Gaurav Mantri Oct 28 '15 at 06:36
Yes it worked perfectly and like as usual you rocked in azure ans.but 1 thing i would like to know that why you have written in your answer that "I am not sure that this is the best code"? – I Love Stackoverflow Oct 28 '15 at 06:49
1

So 2 things here - 1) Personally I don't like performing IO intensive operations (like zipping) in web application itself as I think it's not scalable. What if you are asked to zip 100 files and each file is say 10MB each. I would rather do this via a background job, create the zip file there and push it in blob storage and let the user know somehow. 2) In my code, I am not disposing the memory stream. I'm really not sure the implication of that (this is the 1st time I did something like this). Hence the comment about not being the best code :). – Gaurav Mantri Oct 28 '15 at 07:04
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/93562/discussion-between-learning-and-gaurav-mantri). – I Love Stackoverflow Oct 28 '15 at 07:07
Actually sir i have just started learning azure so just wanted to ask you something related to azure if you are not busy. – I Love Stackoverflow Oct 28 '15 at 07:18

Not able to properly download files from azure storage and data are lost too when downloading files

3 Answers3