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bazel-lib/lib/private/base64.bzl
Jason Bedard 47dd4ce9fd chore: run buildifier
2023-06-13 16:28:17 -07:00

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6.2 KiB
Python
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"""Base64 encoder/decoder utility for Starlark
Handles string only and not binary data
Implementation based on https://gist.github.com/trondhumbor/ce57c0c2816bb45a8fbb but adapted to use
the subset of python available in Starlark.
"""
load(":strings.bzl", "chr", "ord")
def decode(data):
"""Decode a Base64 encoded string.
See https://en.wikipedia.org/wiki/Base64.
Args:
data: base64 encoded string
Returns:
A string containing the decoded data
"""
padding = data.count("=")
data = data.replace("=", "A")
binstring = ""
for i in range(len(data)):
index = BASE64_CHARS.find(data[i])
if index == -1:
fail("expected a base64 encoded string")
binstring += _int_to_binary(index, 6)
eight_chunks = _chunk(binstring, 8)
outstring = ""
for chunk in eight_chunks:
outstring += chr(int(chunk, 2))
return outstring if padding == 0 else outstring[:-padding]
def encode(data):
"""Base64 encode a string.
See https://en.wikipedia.org/wiki/Base64.
Args:
data: string to encode
Returns:
The base64 encoded string
"""
padding = 0
if len(data) % 3 != 0:
padding = (len(data) + 3 - len(data) % 3) - len(data)
data += "\0" * padding
three_chunks = _chunk(data, 3)
binstring = ""
for chunk in three_chunks:
for i in range(len(chunk)):
binstring += _int_to_binary(ord(chunk[i]))
six_chunks = _chunk(binstring, 6)
outstring = ""
for element in six_chunks:
outstring += BASE64_CHARS[int(element, 2)]
return outstring if padding == 0 else outstring[:-padding] + "=" * padding
def _chunk(data, length):
return [data[i:i + length] for i in range(0, len(data), length)]
BASE64_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
# Starlark support octal values that we can leverage for this conversion.
# Generated by lib/private/string.py utility script.
INT_TO_BINARY = [
"00000000",
"00000001",
"00000010",
"00000011",
"00000100",
"00000101",
"00000110",
"00000111",
"00001000",
"00001001",
"00001010",
"00001011",
"00001100",
"00001101",
"00001110",
"00001111",
"00010000",
"00010001",
"00010010",
"00010011",
"00010100",
"00010101",
"00010110",
"00010111",
"00011000",
"00011001",
"00011010",
"00011011",
"00011100",
"00011101",
"00011110",
"00011111",
"00100000",
"00100001",
"00100010",
"00100011",
"00100100",
"00100101",
"00100110",
"00100111",
"00101000",
"00101001",
"00101010",
"00101011",
"00101100",
"00101101",
"00101110",
"00101111",
"00110000",
"00110001",
"00110010",
"00110011",
"00110100",
"00110101",
"00110110",
"00110111",
"00111000",
"00111001",
"00111010",
"00111011",
"00111100",
"00111101",
"00111110",
"00111111",
"01000000",
"01000001",
"01000010",
"01000011",
"01000100",
"01000101",
"01000110",
"01000111",
"01001000",
"01001001",
"01001010",
"01001011",
"01001100",
"01001101",
"01001110",
"01001111",
"01010000",
"01010001",
"01010010",
"01010011",
"01010100",
"01010101",
"01010110",
"01010111",
"01011000",
"01011001",
"01011010",
"01011011",
"01011100",
"01011101",
"01011110",
"01011111",
"01100000",
"01100001",
"01100010",
"01100011",
"01100100",
"01100101",
"01100110",
"01100111",
"01101000",
"01101001",
"01101010",
"01101011",
"01101100",
"01101101",
"01101110",
"01101111",
"01110000",
"01110001",
"01110010",
"01110011",
"01110100",
"01110101",
"01110110",
"01110111",
"01111000",
"01111001",
"01111010",
"01111011",
"01111100",
"01111101",
"01111110",
"01111111",
"10000000",
"10000001",
"10000010",
"10000011",
"10000100",
"10000101",
"10000110",
"10000111",
"10001000",
"10001001",
"10001010",
"10001011",
"10001100",
"10001101",
"10001110",
"10001111",
"10010000",
"10010001",
"10010010",
"10010011",
"10010100",
"10010101",
"10010110",
"10010111",
"10011000",
"10011001",
"10011010",
"10011011",
"10011100",
"10011101",
"10011110",
"10011111",
"10100000",
"10100001",
"10100010",
"10100011",
"10100100",
"10100101",
"10100110",
"10100111",
"10101000",
"10101001",
"10101010",
"10101011",
"10101100",
"10101101",
"10101110",
"10101111",
"10110000",
"10110001",
"10110010",
"10110011",
"10110100",
"10110101",
"10110110",
"10110111",
"10111000",
"10111001",
"10111010",
"10111011",
"10111100",
"10111101",
"10111110",
"10111111",
"11000000",
"11000001",
"11000010",
"11000011",
"11000100",
"11000101",
"11000110",
"11000111",
"11001000",
"11001001",
"11001010",
"11001011",
"11001100",
"11001101",
"11001110",
"11001111",
"11010000",
"11010001",
"11010010",
"11010011",
"11010100",
"11010101",
"11010110",
"11010111",
"11011000",
"11011001",
"11011010",
"11011011",
"11011100",
"11011101",
"11011110",
"11011111",
"11100000",
"11100001",
"11100010",
"11100011",
"11100100",
"11100101",
"11100110",
"11100111",
"11101000",
"11101001",
"11101010",
"11101011",
"11101100",
"11101101",
"11101110",
"11101111",
"11110000",
"11110001",
"11110010",
"11110011",
"11110100",
"11110101",
"11110110",
"11110111",
"11111000",
"11111001",
"11111010",
"11111011",
"11111100",
"11111101",
"11111110",
"11111111",
]
def _int_to_binary(i, digits = 8):
if i < 0 or i > 255:
fail("expected a int between 0 and 255 (inclusive)")
if digits < 1 or digits > 8:
fail("expected digits to be between 1 and 8 (inclusive)")
return INT_TO_BINARY[i][8 - digits:]
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