Streaming file upload using bottle (or flask or similar)

Question

I have a REST frontend written using Python/Bottle which handles file uploads, usually large ones. The API is wirtten in such a way that:

The client sends PUT with t

Answer 1

I recommend splitting the incoming file into smaller-sized chunks on the frontend. I'm doing this to implement a pause/resume function for large file uploads in a Flask application.

Using Sebastian Tschan's jquery plugin, you can implement chunking by specifying a maxChunkSize when initializing the plugin, as in:

$('#file-select').fileupload({
    url: '/uploads/',
    sequentialUploads: true,
    done: function (e, data) {
        console.log("uploaded: " + data.files[0].name)
    },
    maxChunkSize: 1000000 // 1 MB
});

Now the client will send multiple requests when uploading large files. And your server-side code can use the Content-Range header to patch the original large file back together. For a Flask application, the view might look something like:

# Upload files
@app.route('/uploads/', methods=['POST'])
def results():

    files = request.files

    # assuming only one file is passed in the request
    key = files.keys()[0]
    value = files[key] # this is a Werkzeug FileStorage object
    filename = value.filename

    if 'Content-Range' in request.headers:
        # extract starting byte from Content-Range header string
        range_str = request.headers['Content-Range']
        start_bytes = int(range_str.split(' ')[1].split('-')[0])

        # append chunk to the file on disk, or create new
        with open(filename, 'a') as f:
            f.seek(start_bytes)
            f.write(value.stream.read())

    else:
        # this is not a chunked request, so just save the whole file
        value.save(filename)

    # send response with appropriate mime type header
    return jsonify({"name": value.filename,
                    "size": os.path.getsize(filename),
                    "url": 'uploads/' + value.filename,
                    "thumbnail_url": None,
                    "delete_url": None,
                    "delete_type": None,})

For your particular application, you will just have to make sure that the correct auth headers are still sent with each request.

Hope this helps! I was struggling with this problem for a while ;)

Answer 2

When using plupload solution might be like this one:

$("#uploader").plupload({
    // General settings
    runtimes : 'html5,flash,silverlight,html4',
    url : "/uploads/",

    // Maximum file size
    max_file_size : '20mb',

    chunk_size: '128kb',

    // Specify what files to browse for
    filters : [
        {title : "Image files", extensions : "jpg,gif,png"},
    ],

    // Enable ability to drag'n'drop files onto the widget (currently only HTML5 supports that)
    dragdrop: true,

    // Views to activate
    views: {
        list: true,
        thumbs: true, // Show thumbs
        active: 'thumbs'
    },

    // Flash settings
    flash_swf_url : '/static/js/plupload-2.1.2/js/plupload/js/Moxie.swf',

    // Silverlight settings
    silverlight_xap_url : '/static/js/plupload-2.1.2/js/plupload/js/Moxie.xap'
});

And your flask-python code in such case would be similar to this:

from werkzeug import secure_filename

# Upload files
@app.route('/uploads/', methods=['POST'])
def results():
    content = request.files['file'].read()
    filename = secure_filename(request.values['name'])

    with open(filename, 'ab+') as fp:
        fp.write(content)

    # send response with appropriate mime type header
    return jsonify({
        "name": filename,
        "size": os.path.getsize(filename),
        "url": 'uploads/' + filename,})

Plupload always sends chunks in exactly same order, from first to last, so you do not have to bother with seek or anything like that.