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# <!-- rdoc-file=lib/base64.rb -->
# Module Base64 provides methods for:
#
# *   Encoding a binary string (containing non-ASCII characters) as a string of
#     printable ASCII characters.
# *   Decoding such an encoded string.
#
# Base64 is commonly used in contexts where binary data is not allowed or
# supported:
#
# *   Images in HTML or CSS files, or in URLs.
# *   Email attachments.
#
# A Base64-encoded string is about one-third larger that its source. See the
# [Wikipedia article](https://en.wikipedia.org/wiki/Base64) for more
# information.
#
# This module provides three pairs of encode/decode methods. Your choices among
# these methods should depend on:
#
# *   Which character set is to be used for encoding and decoding.
# *   Whether "padding" is to be used.
# *   Whether encoded strings are to contain newlines.
#
# Note: Examples on this page assume that the including program has executed:
#
#     require 'base64'
#
# ## Encoding Character Sets
#
# A Base64-encoded string consists only of characters from a 64-character set:
#
# *   `('A'..'Z')`.
# *   `('a'..'z')`.
# *   `('0'..'9')`.
# *   `=`, the 'padding' character.
# *   Either:
#     *   `%w[+ /]`:
#         [RFC-2045-compliant](https://datatracker.ietf.org/doc/html/rfc2045);
#         *not* safe for URLs.
#     *   `%w[- _]`:
#         [RFC-4648-compliant](https://datatracker.ietf.org/doc/html/rfc4648);
#         safe for URLs.
#
# If you are working with Base64-encoded strings that will come from or be put
# into URLs, you should choose this encoder-decoder pair of RFC-4648-compliant
# methods:
#
# *   Base64.urlsafe_encode64 and Base64.urlsafe_decode64.
#
# Otherwise, you may choose any of the pairs in this module, including the pair
# above, or the RFC-2045-compliant pairs:
#
# *   Base64.encode64 and Base64.decode64.
# *   Base64.strict_encode64 and Base64.strict_decode64.
#
# ## Padding
#
# Base64-encoding changes a triplet of input bytes into a quartet of output
# characters.
#
# **Padding in Encode Methods**
#
# Padding -- extending an encoded string with zero, one, or two trailing `=`
# characters -- is performed by methods Base64.encode64, Base64.strict_encode64,
# and, by default, Base64.urlsafe_encode64:
#
#     Base64.encode64('s')                         # => "cw==\n"
#     Base64.strict_encode64('s')                  # => "cw=="
#     Base64.urlsafe_encode64('s')                 # => "cw=="
#     Base64.urlsafe_encode64('s', padding: false) # => "cw"
#
# When padding is performed, the encoded string is always of length *4n*, where
# `n` is a non-negative integer:
#
# *   Input bytes of length *3n* generate unpadded output characters of length
#     *4n*:
#
#         # n = 1:  3 bytes => 4 characters.
#         Base64.strict_encode64('123')      # => "MDEy"
#         # n = 2:  6 bytes => 8 characters.
#         Base64.strict_encode64('123456')   # => "MDEyMzQ1"
#
# *   Input bytes of length *3n+1* generate padded output characters of length
#     *4(n+1)*, with two padding characters at the end:
#
#         # n = 1:  4 bytes => 8 characters.
#         Base64.strict_encode64('1234')     # => "MDEyMw=="
#         # n = 2:  7 bytes => 12 characters.
#         Base64.strict_encode64('1234567')  # => "MDEyMzQ1Ng=="
#
# *   Input bytes of length *3n+2* generate padded output characters of length
#     *4(n+1)*, with one padding character at the end:
#
#         # n = 1:  5 bytes => 8 characters.
#         Base64.strict_encode64('12345')    # => "MDEyMzQ="
#         # n = 2:  8 bytes => 12 characters.
#         Base64.strict_encode64('12345678') # => "MDEyMzQ1Njc="
#
# When padding is suppressed, for a positive integer *n*:
#
# *   Input bytes of length *3n* generate unpadded output characters of length
#     *4n*:
#
#         # n = 1:  3 bytes => 4 characters.
#         Base64.urlsafe_encode64('123', padding: false)      # => "MDEy"
#         # n = 2:  6 bytes => 8 characters.
#         Base64.urlsafe_encode64('123456', padding: false)   # => "MDEyMzQ1"
#
# *   Input bytes of length *3n+1* generate unpadded output characters of length
#     *4n+2*, with two padding characters at the end:
#
#         # n = 1:  4 bytes => 6 characters.
#         Base64.urlsafe_encode64('1234', padding: false)     # => "MDEyMw"
#         # n = 2:  7 bytes => 10 characters.
#         Base64.urlsafe_encode64('1234567', padding: false)  # => "MDEyMzQ1Ng"
#
# *   Input bytes of length *3n+2* generate unpadded output characters of length
#     *4n+3*, with one padding character at the end:
#
#         # n = 1:  5 bytes => 7 characters.
#         Base64.urlsafe_encode64('12345', padding: false)    # => "MDEyMzQ"
#         # m = 2:  8 bytes => 11 characters.
#         Base64.urlsafe_encode64('12345678', padding: false) # => "MDEyMzQ1Njc"
#
# **Padding in Decode Methods**
#
# All of the Base64 decode methods support (but do not require) padding.
#
# Method Base64.decode64 does not check the size of the padding:
#
#     Base64.decode64("MDEyMzQ1Njc") # => "01234567"
#     Base64.decode64("MDEyMzQ1Njc=") # => "01234567"
#     Base64.decode64("MDEyMzQ1Njc==") # => "01234567"
#
# Method Base64.strict_decode64 strictly enforces padding size:
#
#     Base64.strict_decode64("MDEyMzQ1Njc")   # Raises ArgumentError
#     Base64.strict_decode64("MDEyMzQ1Njc=")  # => "01234567"
#     Base64.strict_decode64("MDEyMzQ1Njc==") # Raises ArgumentError
#
# Method Base64.urlsafe_decode64 allows padding in `str`, which if present, must
# be correct: see [Padding](Base64.html#module-Base64-label-Padding), above:
#
#     Base64.urlsafe_decode64("MDEyMzQ1Njc") # => "01234567"
#     Base64.urlsafe_decode64("MDEyMzQ1Njc=") # => "01234567"
#     Base64.urlsafe_decode64("MDEyMzQ1Njc==") # Raises ArgumentError.
#
# ## Newlines
#
# An encoded string returned by Base64.encode64 or Base64.urlsafe_encode64 has
# an embedded newline character after each 60-character sequence, and, if
# non-empty, at the end:
#
#     # No newline if empty.
#     encoded = Base64.encode64("\x00" *  0)
#     encoded.index("\n") # => nil
#
#     # Newline at end of short output.
#     encoded = Base64.encode64("\x00" *  1)
#     encoded.size        # => 4
#     encoded.index("\n") # => 4
#
#     # Newline at end of longer output.
#     encoded = Base64.encode64("\x00" * 45)
#     encoded.size        # => 60
#     encoded.index("\n") # => 60
#
#     # Newlines embedded and at end of still longer output.
#     encoded = Base64.encode64("\x00" * 46)
#     encoded.size                          # => 65
#     encoded.rindex("\n")                  # => 65
#     encoded.split("\n").map {|s| s.size } # => [60, 4]
#
# The string to be encoded may itself contain newlines, which are encoded as
# Base64:
#
#       #   Base64.encode64("\n\n\n") # => "CgoK\n"
#     s = "This is line 1\nThis is line 2\n"
#     Base64.encode64(s) # => "VGhpcyBpcyBsaW5lIDEKVGhpcyBpcyBsaW5lIDIK\n"
#
module Base64
  # <!--
  #   rdoc-file=lib/base64.rb
  #   - decode64(str)
  # -->
  # Returns a string containing the decoding of an RFC-2045-compliant
  # Base64-encoded string `str`:
  #
  #     s = "VGhpcyBpcyBsaW5lIDEKVGhpcyBpcyBsaW5lIDIK\n"
  #     Base64.decode64(s) # => "This is line 1\nThis is line 2\n"
  #
  # Non-Base64 characters in `str` are ignored; see [Encoding Character
  # Set](Base64.html#module-Base64-label-Encoding+Character+Sets) above: these
  # include newline characters and characters `-` and `/`:
  #
  #     Base64.decode64("\x00\n-_") # => ""
  #
  # Padding in `str` (even if incorrect) is ignored:
  #
  #     Base64.decode64("MDEyMzQ1Njc")   # => "01234567"
  #     Base64.decode64("MDEyMzQ1Njc=")  # => "01234567"
  #     Base64.decode64("MDEyMzQ1Njc==") # => "01234567"
  #
  def self?.decode64: (String str) -> String

  # <!--
  #   rdoc-file=lib/base64.rb
  #   - encode64(bin)
  # -->
  # Returns a string containing the RFC-2045-compliant Base64-encoding of `bin`.
  #
  # Per RFC 2045, the returned string may contain the URL-unsafe characters `+` or
  # `/`; see [Encoding Character
  # Set](Base64.html#module-Base64-label-Encoding+Character+Sets) above:
  #
  #     Base64.encode64("\xFB\xEF\xBE") # => "++++\n"
  #     Base64.encode64("\xFF\xFF\xFF") # => "////\n"
  #
  # The returned string may include padding; see
  # [Padding](Base64.html#module-Base64-label-Padding) above.
  #
  #     Base64.encode64('*') # => "Kg==\n"
  #
  # The returned string ends with a newline character, and if sufficiently long
  # will have one or more embedded newline characters; see
  # [Newlines](Base64.html#module-Base64-label-Newlines) above:
  #
  #     Base64.encode64('*') # => "Kg==\n"
  #     Base64.encode64('*' * 46)
  #     # => "KioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioq\nKg==\n"
  #
  # The string to be encoded may itself contain newlines, which will be encoded as
  # ordinary Base64:
  #
  #     Base64.encode64("\n\n\n") # => "CgoK\n"
  #     s = "This is line 1\nThis is line 2\n"
  #     Base64.encode64(s) # => "VGhpcyBpcyBsaW5lIDEKVGhpcyBpcyBsaW5lIDIK\n"
  #
  def self?.encode64: (String bin) -> String

  # <!--
  #   rdoc-file=lib/base64.rb
  #   - strict_decode64(str)
  # -->
  # Returns a string containing the decoding of an RFC-2045-compliant
  # Base64-encoded string `str`:
  #
  #     s = "VGhpcyBpcyBsaW5lIDEKVGhpcyBpcyBsaW5lIDIK"
  #     Base64.strict_decode64(s) # => "This is line 1\nThis is line 2\n"
  #
  # Non-Base64 characters in `str` not allowed; see [Encoding Character
  # Set](Base64.html#module-Base64-label-Encoding+Character+Sets) above: these
  # include newline characters and characters `-` and `/`:
  #
  #     Base64.strict_decode64("\n") # Raises ArgumentError
  #     Base64.strict_decode64('-')  # Raises ArgumentError
  #     Base64.strict_decode64('_')  # Raises ArgumentError
  #
  # Padding in `str`, if present, must be correct:
  #
  #     Base64.strict_decode64("MDEyMzQ1Njc")   # Raises ArgumentError
  #     Base64.strict_decode64("MDEyMzQ1Njc=")  # => "01234567"
  #     Base64.strict_decode64("MDEyMzQ1Njc==") # Raises ArgumentError
  #
  def self?.strict_decode64: (String str) -> String

  # <!--
  #   rdoc-file=lib/base64.rb
  #   - strict_encode64(bin)
  # -->
  # Returns a string containing the RFC-2045-compliant Base64-encoding of `bin`.
  #
  # Per RFC 2045, the returned string may contain the URL-unsafe characters `+` or
  # `/`; see [Encoding Character
  # Set](Base64.html#module-Base64-label-Encoding+Character+Sets) above:
  #
  #     Base64.strict_encode64("\xFB\xEF\xBE") # => "++++\n"
  #     Base64.strict_encode64("\xFF\xFF\xFF") # => "////\n"
  #
  # The returned string may include padding; see
  # [Padding](Base64.html#module-Base64-label-Padding) above.
  #
  #     Base64.strict_encode64('*') # => "Kg==\n"
  #
  # The returned string will have no newline characters, regardless of its length;
  # see [Newlines](Base64.html#module-Base64-label-Newlines) above:
  #
  #     Base64.strict_encode64('*') # => "Kg=="
  #     Base64.strict_encode64('*' * 46)
  #     # => "KioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKg=="
  #
  # The string to be encoded may itself contain newlines, which will be encoded as
  # ordinary Base64:
  #
  #     Base64.strict_encode64("\n\n\n") # => "CgoK"
  #     s = "This is line 1\nThis is line 2\n"
  #     Base64.strict_encode64(s) # => "VGhpcyBpcyBsaW5lIDEKVGhpcyBpcyBsaW5lIDIK"
  #
  def self?.strict_encode64: (String bin) -> String

  # <!--
  #   rdoc-file=lib/base64.rb
  #   - urlsafe_decode64(str)
  # -->
  # Returns the decoding of an RFC-4648-compliant Base64-encoded string `str`:
  #
  # `str` may not contain non-Base64 characters; see [Encoding Character
  # Set](Base64.html#module-Base64-label-Encoding+Character+Sets) above:
  #
  #     Base64.urlsafe_decode64('+')  # Raises ArgumentError.
  #     Base64.urlsafe_decode64('/')  # Raises ArgumentError.
  #     Base64.urlsafe_decode64("\n") # Raises ArgumentError.
  #
  # Padding in `str`, if present, must be correct: see
  # [Padding](Base64.html#module-Base64-label-Padding), above:
  #
  #     Base64.urlsafe_decode64("MDEyMzQ1Njc") # => "01234567"
  #     Base64.urlsafe_decode64("MDEyMzQ1Njc=") # => "01234567"
  #     Base64.urlsafe_decode64("MDEyMzQ1Njc==") # Raises ArgumentError.
  #
  def self?.urlsafe_decode64: (String str) -> String

  # <!--
  #   rdoc-file=lib/base64.rb
  #   - urlsafe_encode64(bin, padding: true)
  # -->
  # Returns the RFC-4648-compliant Base64-encoding of `bin`.
  #
  # Per RFC 4648, the returned string will not contain the URL-unsafe characters
  # `+` or `/`, but instead may contain the URL-safe characters `-` and `_`; see
  # [Encoding Character
  # Set](Base64.html#module-Base64-label-Encoding+Character+Sets) above:
  #
  #     Base64.urlsafe_encode64("\xFB\xEF\xBE") # => "----"
  #     Base64.urlsafe_encode64("\xFF\xFF\xFF") # => "____"
  #
  # By default, the returned string may have padding; see
  # [Padding](Base64.html#module-Base64-label-Padding), above:
  #
  #     Base64.urlsafe_encode64('*') # => "Kg=="
  #
  # Optionally, you can suppress padding:
  #
  #     Base64.urlsafe_encode64('*', padding: false) # => "Kg"
  #
  # The returned string will have no newline characters, regardless of its length;
  # see [Newlines](Base64.html#module-Base64-label-Newlines) above:
  #
  #     Base64.urlsafe_encode64('*') # => "Kg=="
  #     Base64.urlsafe_encode64('*' * 46)
  #     # => "KioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKioqKg=="
  #
  def self?.urlsafe_encode64: (String bin, ?padding: boolish) -> String
end