Generate multipart data in Python3

README.md

Wrote this. Turns out I don't need it at all since urllib3 has the exact same function. welp.

multipart.py

import unittest
from os import urandom
from io import BytesIO
from binascii import b2a_base64, hexlify


def is_bytes_like(input):
    """Returns true of input is a byte-like object"""
    return hasattr(input, "decode")


def create_multipart(multi):
    """
    Creates a multipart form data and its MIME type

    data is a dictionary {name: (data, type, filename)}

    name is written to the name field on Content-Disposition subheader
    data is data as byte-like object or string. Byte-like object is encoded to base64 while strings are encoded as utf8.
    type is Content-Type of the data
    filename is written to the filename field on Content-Disposition subheader
    All fields in tuple are optional except data. However, they must be filled with a falsy value such as None

    returns (mime_type, multipart_data)
    mime_type is a string you use for request's Content-Type header
    multipart_data is a byte-like object that contains the multipart data
    """
    boundary = hexlify(urandom(16))
    output = BytesIO()

    for key, (data, type, filename) in multi.items():
        output.write(b"--")
        output.write(boundary)
        output.write(b"\r\n")

        output.write(b'Content-Disposition:form-data;name="')
        output.write(key.encode("ascii"))
        output.write(b'";')
        if filename:
            output.write(b'filename="')
            output.write(filename.encode("ascii"))
            output.write(b'"')
        output.write(b"\r\n")

        if type:
            output.write(b"Content-Type:")
            output.write(type.encode("ascii"))
            output.write(b"\r\n")

        output.write(
            b2a_base64(data, newline=False)
            if is_bytes_like(data)
            else data.encode("utf-8")
        )
        output.write(b"\r\n")

    output.write(b"--")
    output.write(boundary)
    output.write(b"--")

    content_type = b"Content-Type:multipart/form-data;boundary=" + boundary
    return content_type.decode("ascii"), output.getvalue()


class MultipartTest(unittest.TestCase):
    """A little unit test for multipart data"""

    def test_general(self):
        mime, output = create_multipart(
            {
                "name": ("John Doe", None, None),
                "result": ("Lorem ipsum...", "text/plain", None),
                "attachment": (b"FILE", None, "file.txt"),
            }
        )
        # get boundary
        import re

        boundary = re.search(r"boundary=([0-9a-f]+)$", mime)[1]
        boundary = "--" + boundary
        self.maxDiff = None
        self.assertMultiLineEqual(
            output.decode("utf-8"),
            (
                boundary
                + "\r\n"
                + 'Content-Disposition:form-data;name="name";\r\n'
                + "John Doe"
                + "\r\n"
                + boundary
                + "\r\n"
                + 'Content-Disposition:form-data;name="result";\r\n'
                + "Content-Type:text/plain\r\n"
                + "Lorem ipsum..."
                + "\r\n"
                + boundary
                + "\r\n"
                + 'Content-Disposition:form-data;name="attachment";filename="file.txt"\r\n'
                + "RklMRQ=="
                + "\r\n"
                + boundary
                + "--"
            ),
        )


if __name__ == "__main__":
    unittest.main()