How to upload multiple answers with image bytestring data?

Question

According to Consumer Surveys docs, the questions[].images[].data field takes a bytes datatype.

I'm using Python 3 for implementation, but the API is giving errors like Invalid ByteString or bytes type is not JSON serializable.

I'm using the following code:

    import base64
    import urllib
    url = 'http://example.com/image.png'
    raw_img = urllib.request.urlopen(url).read()

    # is not JSON serializable due to json serializer not being able to serialize raw bytes
    img_data = raw_img

    # next errors: Invalid ByteString, when tried with base64 encoding as followings:
    img_data = base64.b64encode(raw_img)
    # Also tried decoding it to UTF.8 `.decode('utf-8')`

img_data is part of the JSON payload that is being sent to the API.

Am I missing something? what's the correct way to handle image data upload for questions? I looked into https://github.com/google/consumer-surveys/tree/master/python/src but there is not example of this part.

Thanks

Answer 1

You need to use web-safe/URL-safe encoding. Here's some documentation on doing this in Python: https://pymotw.com/2/base64/#url-safe-variations

In your case, this would look like

img_data = base64.urlsafe_b64encode(raw_img)

ETA: In Python 3, the API expects the image data to be of type str so it can be JSON serialized, but the base64.urlsafe_b64encode method returns the data in the form of UTF-8 bytes. You can fix this by converting the bytes to Unicode:

img_data = base64.urlsafe_b64encode(raw_img)
img_data = img_data.decode('utf-8')