Return binary HTTP response from OpenWhisk (IBM Cloud Function) action

Question

I want to return a binary file which resides in (IBM Cloud) ObjectStorage via HTTP using OpenWhisk in a IBM Cloud Function.

Is this possible? To me it seems OpenWhisk only supports JSON as result to an action.

This is the code I'm using (get_object_storage_file returns binary data):

import sys
from io import StringIO
import requests
import json

def get_object_storage_file(container, filename):
    """This functions returns a StringIO object containing
    the file content from Bluemix Object Storage."""

    url1 = ''.join(['https://identity.open.softlayer.com', '/v3/auth/tokens'])
    data = {'auth': {'identity': {'methods': ['password'],
            'password': {'user': {'name': 'member_1feaf9dc308e9d57b5fce8a2424e51cd3f04af17','domain': {'id': '4619da2fa8524beda11c89d2d1969c5b'},
            'password': 'nviJ.XXXXXXX.aexT'}}}}}
    headers1 = {'Content-Type': 'application/json'}
    resp1 = requests.post(url=url1, data=json.dumps(data), headers=headers1)
    resp1_body = resp1.json()
    for e1 in resp1_body['token']['catalog']:
        if(e1['type']=='object-store'):
            for e2 in e1['endpoints']:
                        if(e2['interface']=='public'and e2['region']=='dallas'):
                            url2 = ''.join([e2['url'],'/', container, '/', filename])
    s_subject_token = resp1.headers['x-subject-token']
    headers2 = {'X-Auth-Token': s_subject_token, 'accept': 'application/json'}
    resp2 = requests.get(url=url2, headers=headers2)
    return StringIO(resp2.text)

def main(dict):
    get_object_storage_file('data', 'raw.bin')
    return {'greeting':'test'}

Answer 1

Is this about a web-action or a "normal" action?

In general, you can always return a Base64 encoded representation of your binary data, encoded in a JSON object. It is true, that a CloudFunctions action always needs to return a JSON object.

In your specific example, the following could work:

import base64

def main(dict):
    binary = get_object_storage_file('data', 'raw.bin')
    return {'data':base64.base64encode(binary)}

(untested pseudocode)