drf Base64Field with optional format

field.py

import base64

import binascii

from django.core.files.base import ContentFile
from django.utils import six

from rest_framework.exceptions import ValidationError
from rest_framework.fields import FileField


class Base64FieldMixin:
    EMPTY_VALUES = (None, '', [], (), {})

    def __init__(self, *args, **kwargs):
        self.represent_in_base64 = kwargs.pop('represent_in_base64', False)
        super(Base64FieldMixin, self).__init__(*args, **kwargs)

    def to_internal_value(self, base64_data):
        # Check if this is a base64 string
        if base64_data in self.EMPTY_VALUES:
            return None

        if isinstance(base64_data, six.string_types):
            # Strip base64 header.
            if ';base64,' in base64_data:
                header, base64_data = base64_data.split(';base64,')

            try:
                base64_data, file_name = base64_data.split(';file_name')
            except ValueError:
                raise ValidationError('Does not provide file name at the end of base64 string.'
                                      'Supported format is '
                                      '"base64string;file_name:name_with_file_extension".'
                                      'Example "5647676isoiuahkdjvbsad;filename:my_file.pdf')

            # Try to decode the file. Return validation error if it fails.
            try:
                decoded_file = base64.b64decode(base64_data)
            except (TypeError, binascii.Error):
                raise ValidationError('Invalid base64 encoding')

            data = ContentFile(decoded_file, name=file_name)
            return super(Base64FieldMixin, self).to_internal_value(data)
        raise ValidationError('This is not an base64 string')

    def to_representation(self, file):
        if self.represent_in_base64:
            try:
                with open(file.path, 'rb') as f:
                    return base64.b64encode(f.read()).decode()
            except Exception:
                raise IOError("Error encoding file")
        else:
            return super(Base64FieldMixin, self).to_representation(file)


class Base64Field(Base64FieldMixin, FileField):
    pass