The objects in request.files are FileStorage objects. They have the same methods as normal file objects in python.

So, to get the contents of the file as binary, just do this:

data = request.files['file'].read()

Then pass that parameter into the INSERT.

Create a response object with the data and then set the content type header. Set the content disposition header to attachment if you want the browser to save the file instead of displaying it.

@app.route('/images/<int:pid>.jpg')
def get_image(pid):
    image_binary = read_image(pid)
    response = make_response(image_binary)
    response.headers.set('Content-Type', 'image/jpeg')
    response.headers.set(
        'Content-Disposition', 'attachment', filename='%s.jpg' % pid)
    return response

Relevant: werkzeug.Headers and flask.Response

You can pass a file-like object and the header arguments to send_file to let it set up the complete response. Use io.BytesIO for binary data:

return send_file(
    io.BytesIO(image_binary),
    mimetype='image/jpeg',
    as_attachment=True,
    download_name='%s.jpg' % pid)

Prior to Flask 2.0, download_name was called attachment_filename.

What you get is form data and I think you want to receive the uploaded file.
Try request.files and you will get a file-like object of type FileStorage. From this you can read the content of the file with read().

file = request.files['file']
data = file.read()

It turns out that sending an attachment is not possible. So I dug deeper into how to send base64-encoded attachments which would then be saved as blobs.

For that I used pre- and post-processing facility of flask_restless:

def pp_get_single_image(result=None, **kw):
    import base64
    result['image'] = base64.b64encode(result['image']).decode('utf8')

def pp_get_many_images(result=None, search_params=None, **kw):
    result['objects'] = [pp_get_single_image(d) or d for d in result['objects']]

def pp_post_image_in(data=None, **kw):
    import base64
    data['image'] = base64.b64decode(data['image'])

def pp_post_image_out(result=None, **kw):
    import base64
    result['image'] = base64.b64encode(result['image']).decode('utf8')

postprocessors=dict(GET_SINGLE=[pp_get_single_image], GET_MANY=[pp_get_many_images], POST=[pp_post_image_out])
preprocessors=dict(POST=[pp_post_image_in])

manager = flask_restless.APIManager(app, flask_sqlalchemy_db=db)
manager.create_api(Image, methods=['GET', 'POST', 'DELETE'],
               postprocessors=pp_image.postprocessors,
               preprocessors=pp_image.preprocessors)

I can only partially answer your question.

For first part use:

f = request.files['file']
bin_file = StringIO.StringIO(f.read())  # or ByteIO, whatever you like
# Now you have file in memory as binary
# I recommend using bin_file.seek(0) before every read/modification/write

I have very limited experience with C and DLL-like code. So I can't give you direct solution. But I can give you some hints how would I solve it.

One of the solution could be passing StringIO/ByteIO as an argument to C/C++ program. I would try using python's subprocess.

Another solution would be writing a python wrapper for your code, calling it directly in python/flask. Again, I have no experience with it.