How to decode ascii encoded image data to an image file?

Question

Overview

Handle decoding of base64 encoded image files in a concise and (relatively) comprehensive way.

Goals

Primary Goal

• Use python 3.6 to take an arbitrary base64 string, whether as an 'in-memory' string or external file, and generate an valid image file from it.

Secondary Goal

• Use libmagic (or some other python library) to determine, as best as is possible, the mime type of an encoded file for directing the correct filetype output.

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Preliminary Assumptions

Encoding is Valid

• A small JPG image was encoded in base64. I have verified that the encoding was good by viewing the encoded data through web browser using the browser's native decoding device for encoded images. See below.

This is Doable in Python 3.6

• Seemingly the base64 package is made for this, unless I'm way off base.

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Attempted Solution

Explaination

I created a python class named Converter to handle the task, with the following features

Constructor

• __init__(self, file="none", str_object="none")
  • Takes 2 string arguments. Only one is to be specified to replace the default depending on desired usage.
  • file="none" - Path to file as a string for file-based decoding.
  • str_object="none" - Naked encoded string.

Instance Methods

• convert_ascii_to_byte_stream(self)
  • No arguments
  • Returns a base64 object
• convert_byte_stream_to_jpg(self)
  • No arguments
  • Opens a new file, attempts to write a byte stream (using convert_ascii_to_byte_stream, then closes the file.
  • Returns nothing
• @staticmethod strip_all_whitespace(s)
  • Takes a single string of arbitrary length.
  • Returns a string with all whitespace, newlines, tabs, and carriage returns removed.

Usage

__main__.py

from Converter import *

c = Converter('ascii_image.txt', 'none')  # create Converter instance
# print(c.get_encoding_type()) # attempt to get encoding
c.convert_byte_stream_to_jpg()  # output the decoded data to image file

Observations and Questions

• If I invoke the constructor Converter('none', 'XyZxYzXyZxYzXyZxYz ...) then the conversion happens flawlessly. Obviously there is a problem with the writing to the file.
• I understand the the prefix to the <img> source attribute, data:image/jpg;base64, must be stripped prior to decoding. Therefore the test file am using ascii_image.txt has been edited to reflect this.
• In the original source there are newlines at the end of each line, and a single blank space at the start of each subsequent line. Not sure if this makes a difference, especially considering that I am stripping ALL whitespace prior to attempting decoding.
• I've tried a bunch of convoluted ways of using libmagic, python-libmagic, python-magic-bin, file-magic, and various other extended packages with much confusion and little progress. Most of them just created a spaghetti stream of error messages about missing dependencies, compiler errors, and other problems. Any suggestions would be appreciated.

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Relevant Code and Error Messages

Converter Python Class

from io import *
import base64
# import magic


class Converter:

    def __init__(self, file="none", str_object="none"):
        self.file = file
        self.str_object = str_object
        if file == "none" or "":
            self.isFromStringInput = True
            self.asciiString = str_object
        else:
            f = open(file, 'r')
            self.isFromStringInput = False
            # this was the source of the pad error
            #self.asciiString = f.read(file.__len__())
            # changed to ... duh!
            self.asciiString = f.read()
            f.close()

    def convert_byte_stream_to_jpg(self):
        f = open('ascii_image.jpg', 'wb')
        f.write(self.convert_ascii_to_byte_stream())
        f.close()
        return

    def convert_ascii_to_byte_stream(self):
        return base64.b64decode(self.strip_all_whitespace(self.asciiString))

    @staticmethod
    def strip_all_whitespace(s):
        return s.replace('\n', ' ').replace('\r', '').replace('\t', '').replace(' ', '')

    # def get_encoding_type(self):
    #     m = magic.MAGIC_MIME
    #     m.from_bytes(self.convert_ascii_to_byte_stream(), 'little')
    #     return m.file('./' + self.file)

Error Message

Traceback (most recent call last):
  File "/Users/auser/PycharmProjects/btobin/__main__.py", line 5, in <module>
    c.convert_byte_stream_to_jpg()  # output the decoded data to image file
  File "/Users/auser/PycharmProjects/btobin/Converter.py", line 22, in convert_byte_stream_to_jpg
    f.write(self.convert_ascii_to_byte_stream())
  File "/Users/auser/PycharmProjects/btobin/Converter.py", line 27, in convert_ascii_to_byte_stream
    return base64.b64decode(self.strip_all_whitespace(self.asciiString))
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/base64.py", line 87, in b64decode
    return binascii.a2b_base64(s)
binascii.Error: Incorrect padding

Correct Encoding Verified

If one places the following <img> tag in an html file and opens it with a browser they will see the properly decoded image. Here is an example of the Decoded Image

<img src="data:image/jpg;base64,/9j/4QAYRXhpZgAASUkqAAgAAAAAAAAAAAAAAP/sABFEdWNr
 eQABAAQAAAAeAAD/4QOPaHR0cDovL25zLmFkb2JlLmNvbS94YXAvMS4wLwA8P3hwYWNrZXQgYm
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 A3OS4xNTY3OTcsIDIwMTQvMDgvMjAtMDk6NTM6MDIgICAgICAgICI+IDxyZGY6UkRGIHhtbG5z
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