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.

Download

To download a file given its _id, use fileStore.download. The response contains a string representation of the file content. If you only need to get the file metadata, use Files.find() or consider streaming the file.

var promise = Kinvey.Files.download('file-id')
  .then(function(file) {
    var fileContent = file;
    // ...
  })
  .catch(function(error) {
    // ...
  });

Stream

If you want to obtain only a download URL and not the file itself, you can use streaming. To stream a file, use fileStore.stream. The response will contain the file metadata, with the download URL available as _downloadURL property.

var fileStore = new Kinvey.FileStore();
var promise = fileStore.stream('file-id');
promise.then(function(file) {
    var url = file._downloadURL;
    ...
});

Query

To retrieve a list of files, the Querying interface is available for files.

The snippet below retrieves a list of all PNG images. The response is a list of file metadata.

var query = new Kinvey.Query();
query.equalTo('mimeType', 'image/png');
var promise = Kinvey.Files.find(query)
  .then(function(files) {
    // ...
  })
  .catch(function(error) {
    // ...
  });

Optionally, you can add the download: true flag to download every file found. The file itself will then become available under the _data property of each file in the list.

The file metadata returned by any of the methods explained above contains a _downloadURL. Depending on your use case, you might want to re-download a file. The Kinvey.Files.downloadByUrl() method allows you to do just that. The method accepts a _downloadURL.

var promise = Kinvey.Files.download('file-id')
  .then(function(file) {
    // After some time passed, redownload the file.
    return Kinvey.Files.downloadByUrl(file._downloadURL);
  })
  .then(function(fileData) {
    // ...
  })
  .catch(function(error) {
    // ...
  });

Specifying a custom expiration time

If you require the temporary download URL to last longer (or shorter) than the default of one hour, you may optionally specify a custom expiration time (in seconds) using the ttl option. If the file is public, the returned download URL never expires.

var promise = Kinvey.Files.download('file-id', {
  ttl: 7200 // Two hours in ms
})
  .then(function(file) {
    // ...
  })
  .catch(function(error) {
    // ...
  });

Upload

Use Kinvey.Files.upload() to upload the file and, optionally, save any associated metadata along with it. The example below uploads a file represented as a string. The _id and _filename properties will be auto-generated by Kinvey if left out.

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

var fileContent = '<file-content>';
var metadata ={
  _id: '<file-id>',
  filename: '<filename>',
  mimeType: '<mime-type>'
};
var promise = Kinvey.Files.upload(fileContent, metadata)
  .then(function(file) {
    // ...
  })
  .catch(function(error) {
    // ...
  });

Delete

To delete a file, use Kinvey.Files.removeById().

var promise = Kinvey.Files.removeById('file-id')
  .then(function(result) {
    // ...
  })
  .catch(function(error) {
    // ...
  });

Linking files to entities in collections

Many common uses for files involve associating them with entities that reside in collections. In order to make this experience as easy as possible, entities in collections may contain KinveyFile references. These references will be automatically resolved when the entity that contains them is retrieved through the Data Store API.

Creating a KinveyFile reference

A reference to a file stored using Kinvey, or a KinveyFile reference, is simply a JSON object with a _type of KinveyFile and an _id containing the ID of a file in Kinvey (as created through the File API).

To store a KinveyFile reference, create or update an entity in any collection with such a property. For example:

var dataStore = Kinvey.DataStore.collection('pets');
dataStore.save({
  dogName: 'Bob',
  furColor: 'brown with black spots',
  pawPrintPicture: {
    _type: 'KinveyFile',
    _id: '325620e4-93dd-4a26-9f84-8a5e62c0db11'
  }
})
  .then(function(pet) {
    // ...
  })
  .catch(function(error) {
    // ...
  });

Please note that only two properties are allowed in a KinveyFile reference: _type and _id. If you attempt to save any additional properties as part of the KinveyFile JSON object, these properties will be ignored by Kinvey and not saved. Any additional properties that you wish to assiciate with the file should be a part of the file itself, and set through the File API.

Downloading using a KinveyFile reference

When querying any collection through the Data Store API, Kinvey will resolve any KinveyFile reference and provide you with a _downloadURL.

var dataStore = Kinvey.DataStore.collection('pets');
dataStore.findById('3f583e9f-d064-4a25-a953-6cf0a3dc2ff1')
  .subscribe(function(pet) {
    /*
      {
        "_id": "3f583e9f-d064-4a25-a953-6cf0a3dc2ff1",
        "_acl": {...},
        "dogName": "Bob",
        "furColor": "brown with black spots",
        "pawPrintPicture": {
          "_type": "KinveyFile",
          "_id": "325620e4-93dd-4a26-9f84-8a5e62c0db11",
          "_filename": "bobsPawPrint.png",
          "_acl": { ... },
          "_downloadURL": <Google Cloud Storage download URL>,
          "_expiresAt": "2018-06-18T23:07:23.394Z"
        }
      }
    */
  }, function(error) {
    // ...
  });

You will then need to download the file directly from Google Cloud Storage by calling Kinvey.Files.downloadByUrl(); with the _downloadURL property of the KinveyFiles reference.

Specifying a custom expiration time using KinveyFiles

If you require the temporary download URL to last longer (or shorter) than one hour, you may optionally specify a custom expiration time (in seconds) using the kinveyFileTTL query parameter.

var dataStore = Kinvey.DataStore.collection('pets');
dataStore.findById('3f583e9f-d064-4a25-a953-6cf0a3dc2ff1', { kinveyFileTTL: 3600 })
  .subscribe(function(pet) {
    /*
      {
        "_id": "3f583e9f-d064-4a25-a953-6cf0a3dc2ff1",
        "_acl": {...},
        "dogName": "Bob",
        "furColor": "brown with black spots",
        "pawPrintPicture": {
          "_type": "KinveyFile",
          "_id": "325620e4-93dd-4a26-9f84-8a5e62c0db11",
          "_filename": "bobsPawPrint.png",
          "_acl": { ... },
          "_downloadURL": <Google Cloud Storage download URL>,
          "_expiresAt": "2018-06-18T23:07:23.394Z"
        }
      }
    */
  }, function(error) {
    // ...
  });

If you would like to upload a publicly-readable file that never expires, please refer to the upload publicly-readable files section.

Securely communicating with GCS using KinveyFiles

Secure communication is available as a query parameter when retrieving KinveyFile references through the Data Store API, as well. To use https instead of http, set the kinveyFileTLS parameter to true.

var dataStore = Kinvey.DataStore.collection('pets');
dataStore.findById('3f583e9f-d064-4a25-a953-6cf0a3dc2ff1', { kinveyFileTLS: true })
  .subscribe(function(pet) {
    /*
      {
        "_id": "3f583e9f-d064-4a25-a953-6cf0a3dc2ff1",
        "_acl": {...},
        "dogName": "Bob",
        "furColor": "brown with black spots",
        "pawPrintPicture": {
          "_type": "KinveyFile",
          "_id": "325620e4-93dd-4a26-9f84-8a5e62c0db11",
          "_filename": "bobsPawPrint.png",
          "_acl": { ... },
          "_downloadURL": <Google Cloud Storage download URL>,
          "_expiresAt": "2018-06-18T23:07:23.394Z"
        }
      }
    */
  }, function(error) {
    // ...
  });

Business Logic

You may create Business Logic code which will execute before or after each File API v3 route. To do so, simply add hooks to the _blob collection just like any other data collection. For more information on Business Logic, refer to the Business Logic guide.

Comprehensive reference

Properties

While you may include any number of custom metadata properties when saving your file, Kinvey uses certain properties to maintain its own metadata. This section contains a comprehensive list of all special Kinvey attributes that may be part of a file.

Special supported properties

The following properties, while optional, will allow the Kinvey Console to display more information about the file if you specify them as part of the file metadata.

Optional query parameters