decode Data URI to mime and data parts

daturi.py

#!/usr/bin/env python
# Convert a data uri file into the data part
#
# Usage: daturi.py infile
#
# Copy a response from Chrome
#   pbaste > foo
#   daturi.py foo
# creates foo.mimetype

import base64
import sys

def decodeDataUri(uristr):
  comma = uristr.find(',')
  urihead = uristr.find('data:')

  if urihead is None or comma is None:
    return None
  headpart = uristr[urihead + 5:comma]
  firstsep = headpart.find(';')

  if firstsep is None:
    firstsep = len(firstsep)

  mimetype = headpart[0:firstsep]
  b64data = uristr[(comma + 1):]
  rawdata = base64.b64decode(b64data)

  return ( mimetype, rawdata )

with open(sys.argv[1], 'r') as my_file:
    mime, data = decodeDataUri(my_file.read())
    mime = mime.replace('/', '.')
    with open(sys.argv[1] + "." + mime, 'wb') as out_file:
       out_file.write(data);

This can be adapted into a Service on MacOS but it isn't especially satisfying if you're trying to get it direct from the browser.