Files

You can use Kinvey to store and retrieve binary files of size up to 5TB. Files can be of any format.

The files are automatically enabled for download using a Content Delivery Network (CDN) for massive scale and performance.

Kinvey does not directly serve or accept files. Instead, the Kinvey Files API works by providing a short-lived URL to a third-party cloud storage service from which file(s) can be uploaded or downloaded. Currently, the third-party service used is Google Cloud Storage.

You would typically use the Files API to upload and download:

images
video files
other application-specific files.

Uploading

The library's File API supports uploading a byte[] directly as well as streaming content from an Stream. To upload a file, use myClient.File().upload(). Pass a FileMetaData object, the file contents. FileMetaData lets you set ACLs, mark files as public, and set any other custom attributes your app may need.

When using custom values for _id, you should avoid values that are exactly 12 or 24 symbols in length. Such values are automatically converted to BSON ObjectID and are not stored as strings in the database, which can interfere with querying and other operations.

To ensure that no items with 12 or 24 symbols long _id are stored in the collection, you can create a pre-save hook that either prevents saving such items, or appends an additional symbol (for example, underscore) to the _id:

if (_id.length === 12 || _id.length === 24) {
  _id += "_";
}

Stream

var content = System.IO.File.ReadAllBytes(your_file_path);
var contentSize = content.Length * sizeof(byte);
var fileMetaData = new FileMetaData
{
    fileName = your_file_name,
    _public = true,
    size = contentSize
};
var streamContent = new MemoryStream(content);
var fmd = await kinveyClient.File().uploadAsync(fileMetaData, streamContent);

Byte array (Upload)

var byteArrayContent = System.IO.File.ReadAllBytes(your_file_path);
var contentSize = (content.Length) * sizeof(byte);
var fileMetaData = new FileMetaData
{
    fileName = your_file_name,
    _public = true,
    size = contentSize
};
var fmd = await kinveyClient.File().uploadAsync(fileMetaData, byteArrayContent);

Uploading publicly readable files

Use the method fileMetaData._public = true if you want to upload a publicly-readable file. This means that the download link to the file will not expire until you delete the file through Kinvey.

var fileMetaData = new FileMetaData
{
    _public = true
};

Downloading

The library's File API supports downloading a File into a byte[] directly as well as streaming content from an Stream. To download a file, use myClient.File().download(). Pass a FileMetaData object, and the location of the file you want. FileMetaData requires an _id to determine which file to download.

Stream

You can download a file directly to a Stream.

var downloadMetaData = await kinveyClient.File()
                            .downloadMetadataAsync(uploadFMD.id);
downloadMetaData.id = uploadFMD.id;
using (var downloadStreamContent = new MemoryStream())
{
    var downloadFMD = await kinveyClient.File()
                            .DownloadAsync(downloadMetaData, downloadStreamContent);
    using (var fs = new FileStream(downloadStreamFilePath, FileMode.Create))
    {
        downloadStreamContent.WriteTo(fs);
    }
}

Byte array (Download)

You can download a file directly into a byte[].

var downloadMetaData = await kinveyClient.File()
                            .downloadMetadataAsync(uploadFMD.id);
downloadMetaData.id = uploadFMD.id;
var downloadContent = new byte[downloadMetaData.size];
var downloadFMD = await kinveyClient
                        .File()
                        .DownloadAsync(downloadMetaData, downloadContent);
System.IO.File.WriteAllBytes(your_file_path, content);

Deleting

You can permanently remove a file using the delete() method.

KinveyDeleteResponse kdr = await kinveyClient.File().delete(fileMetaData.id);

Guides

Files