impl/python/base64_url_decode.py

Imports name this capability’s declared dependencies, which fune builds next to it in your project; each one links to its page.

from typing import List

from .encoding_base64_base64_decode import base64_decode  ← base64Decode, another function of this group · built into the same file, even by a slim install


def base64_url_decode(text: str) -> List[int]:
    """base64url text back to bytes, with or without correct padding."""
    if not isinstance(text, str):
        raise TypeError("base64url text must be a string")
    body = []
    padding = 0
    for ch in text:
        if ch == "=":
            padding += 1
            continue
        ok = ("A" <= ch <= "Z") or ("a" <= ch <= "z") or ("0" <= ch <= "9") or ch == "-" or ch == "_"
        if not ok or padding > 0:
            raise ValueError(
                "base64url text may only contain A-Z, a-z, 0-9, - and _, with optional = padding at the end"
            )
        body.append("+" if ch == "-" else "/" if ch == "_" else ch)
    if len(body) % 4 == 1:
        raise ValueError(
            "base64url text cannot be %d characters long; no number of bytes encodes to that" % len(body)
        )
    needed = (4 - len(body) % 4) % 4
    if padding != 0 and padding != needed:
        raise ValueError("base64url text has the wrong amount of = padding")
    return base64_decode("".join(body) + "=" * needed)