PlantUML url encryption decoder

plant_uml_decoder.py

#!/usr/bin/env python3
import zlib
import base64
import string
import sys

plantuml_alphabet = (
    string.digits + string.ascii_uppercase + string.ascii_lowercase + "-_"
)
base64_alphabet = string.ascii_uppercase + string.ascii_lowercase + string.digits + "+/"
b64_to_plantuml = bytes.maketrans(
    base64_alphabet.encode("utf-8"), plantuml_alphabet.encode("utf-8")
)
plantuml_to_b64 = bytes.maketrans(
    plantuml_alphabet.encode("utf-8"), base64_alphabet.encode("utf-8")
)


def plantuml_encode(plantuml_text):
    """zlib compress the plantuml text and encode it for the plantuml server"""
    zlibbed_str = zlib.compress(plantuml_text.encode("utf-8"))
    compressed_string = zlibbed_str[2:-4]
    return (
        base64.b64encode(compressed_string).translate(b64_to_plantuml).decode("utf-8")
    )


def plantuml_decode(plantuml_url):
    """decode plantuml encoded url back to plantuml text"""
    data = base64.b64decode(plantuml_url.translate(plantuml_to_b64).encode("utf-8"))
    dec = zlib.decompressobj()  # without check the crc.
    header = b"x\x9c"
    return dec.decompress(header + data).decode("utf-8")

if __name__ == "__main__":
    print(plantuml_decode(sys.argv[1]))