Ruby 编码 ASCII_8BIT 和扩展 ASCII

Question

关于ASCII_8BIT

Encoding::ASCII_8BIT is a special encoding that is usually used for a byte string, not a character string. But as the name insists, its characters in the range of ASCII are considered as ASCII characters. This is useful when you use ASCII-8BIT characters with other ASCII compatible characters.

来源:ruby-doc.org/core-2.6.4

上下文

我想使用 ASCII_8BIT，因为我需要对 0x00 (0d00) 和 0xff (0d255) 之间的所有字符进行编码，所以 ASCII (0-127) 加上扩展 ASCII (128-255)。ASCII(编码，US-ASCII)是一种 7 位编码，只能识别 ASCII(字符集)字符 (0-127)。顾名思义，我期望 ASCII_8BIT 会将其扩展到 8 位以添加对 128-255 的支持。

问题

当我使用 chr 时，编码自动设置为 ASCII_8BIT，但是当我将 char 直接放在 128-255 (0x80-0xff) 之间的字符串中，然后询问编码是什么时，我得到的是 UTF-8，如果我尝试将其转换为 ASCII_8BIT 时出现错误。

irb(main):014:0> 0x8f.chr
=> "\x8F"
irb(main):015:0> 0x8f.chr.encoding
=> #<Encoding:ASCII-8BIT>
irb(main):016:0> "\x8f".encode(Encoding::ASCII_8BIT)
Traceback (most recent call last):
        5: from /usr/bin/irb:23:in `<main>'
        4: from /usr/bin/irb:23:in `load'
        3: from /usr/lib/ruby/gems/2.6.0/gems/irb-1.0.0/exe/irb:11:in `<top (required)>'
        2: from (irb):16
        1: from (irb):16:in `encode'
Encoding::InvalidByteSequenceError ("\x8F" on UTF-8)
irb(main):021:0> "\x8F".encoding
=> #<Encoding:UTF-8>

ruby 核心是否存在错误？我需要能够对 8 之间的所有内容进行编码

ASCII 8BIT 的另一个名称是 BINARY，因为如前引述所述，它应该能够编码任何字节。

irb(main):035:0> Encoding::ASCII_8BIT.names
=> ["ASCII-8BIT", "BINARY"]

其他编码

请告诉我使用另一种编码不是问题的答案，除非它是一种真正映射所有 255 个扩展 ASCII 字符的编码。

• 我不想使用 UTF-8，因为编码是多字节而不是单字节。
• ISO/IEC 8859-1(Latin1，8 位)仅包含 191 个字符(ASCII + 63 个字符)

  One notable way in which ISO character sets differ from code pages is that the character positions 128 to 159, corresponding to ASCII control characters with the high-order bit set, are specifically unused and undefined in the ISO standards, though they had often been used for printable characters in proprietary code pages, a breaking of ISO standards that was almost universal. Ref. Extended ASCII- ISO 8859 and proprietary adaptations

• Windows-1252(CP-1252，8 位)不包含所有 255 个字符和扩展 ASCII 的不同映射

可用的 ruby​​ 编码:

irb(main):036:0> Encoding.name_list
=> ["ASCII-8BIT", "UTF-8", "US-ASCII", "UTF-16BE", "UTF-16LE", "UTF-32BE", "UTF-32LE", "UTF-16", "UTF-32", "UTF8-MAC", "EUC-JP", "Windows-31J", "Big5", "Big5-HKSCS", "Big5-UAO", "CP949", "Emacs-Mule", "EUC-KR", "EUC-TW", "GB2312", "GB18030", "GBK", "ISO-8859-1", "ISO-8859-2", "ISO-8859-3", "ISO-8859-4", "ISO-8859-5", "ISO-8859-6", "ISO-8859-7", "ISO-8859-8", "ISO-8859-9", "ISO-8859-10", "ISO-8859-11", "ISO-8859-13", "ISO-8859-14", "ISO-8859-15", "ISO-8859-16", "KOI8-R", "KOI8-U", "Shift_JIS", "Windows-1250", "Windows-1251", "Windows-1252", "Windows-1253", "Windows-1254", "Windows-1257", "BINARY", "IBM437", "CP437", "IBM737", "CP737", "IBM775", "CP775", "CP850", "IBM850", "IBM852", "CP852", "IBM855", "CP855", "IBM857", "CP857", "IBM860", "CP860", "IBM861", "CP861", "IBM862", "CP862", "IBM863", "CP863", "IBM864", "CP864", "IBM865", "CP865", "IBM866", "CP866", "IBM869", "CP869", "Windows-1258", "CP1258", "GB1988", "macCentEuro", "macCroatian", "macCyrillic", "macGreek", "macIceland", "macRoman", "macRomania", "macThai", "macTurkish", "macUkraine", "CP950", "Big5-HKSCS:2008", "CP951", "IBM037", "ebcdic-cp-us", "stateless-ISO-2022-JP", "eucJP", "eucJP-ms", "euc-jp-ms", "CP51932", "EUC-JIS-2004", "EUC-JISX0213", "eucKR", "eucTW", "EUC-CN", "eucCN", "GB12345", "CP936", "ISO-2022-JP", "ISO2022-JP", "ISO-2022-JP-2", "ISO2022-JP2", "CP50220", "CP50221", "ISO8859-1", "ISO8859-2", "ISO8859-3", "ISO8859-4", "ISO8859-5", "ISO8859-6", "Windows-1256", "CP1256", "ISO8859-7", "ISO8859-8", "Windows-1255", "CP1255", "ISO8859-9", "ISO8859-10", "ISO8859-11", "TIS-620", "Windows-874", "CP874", "ISO8859-13", "ISO8859-14", "ISO8859-15", "ISO8859-16", "CP878", "MacJapanese", "MacJapan", "ASCII", "ANSI_X3.4-1968", "646", "UTF-7", "CP65000", "CP65001", "UTF-8-MAC", "UTF-8-HFS", "UCS-2BE", "UCS-4BE", "UCS-4LE", "CP932", "csWindows31J", "SJIS", "PCK", "CP1250", "CP1251", "CP1252", "CP1253", "CP1254", "CP1257", "UTF8-DoCoMo", "SJIS-DoCoMo", "UTF8-KDDI", "SJIS-KDDI", "ISO-2022-JP-KDDI", "stateless-ISO-2022-JP-KDDI", "UTF8-SoftBank", "SJIS-SoftBank", "locale", "external", "filesystem", "internal"]

用于比较 python 编码 https://docs.python.org/3/library/codecs.html#standard-encodings

注意事项

通过阅读Extended ASCII - Multi-byte character encodings似乎唯一真正的扩展 ASCII 编码是 UTF-8 但它是 Multi-byte 。似乎也不存在真正的扩展 ASCII 单字节编码。

从字节的角度来看，我可以使用此处所说的任何 8 位(单字节)编码 Extended ASCII - Usage in computer-readable languages

all ASCII bytes (0x00 to 0x7F) have the same meaning in all variants of extended ASCII,

但问题是像 ISO-8859-1 这样的实现特别未定义一些字符范围，因此会以错误结束。

irb(main):009:0> (0..255).map { |c| c.chr}.join.encode(Encoding::ISO_8859_1)
Traceback (most recent call last):
        6: from /usr/bin/irb:23:in `<main>'
        5: from /usr/bin/irb:23:in `load'
        4: from /usr/lib/ruby/gems/2.6.0/gems/irb-1.0.0/exe/irb:11:in `<top (required)>'
        3: from (irb):9
        2: from (irb):9:in `rescue in irb_binding'
        1: from (irb):9:in `encode'
Encoding::UndefinedConversionError ("\x80" to UTF-8 in conversion from ASCII-8BIT to UTF-8 to ISO-8859-1)

---

更新 - force_encoding

我找到了字符串方法force_encoding .

irb(main)> a = "\x8f"
=> "\x8F"
irb(main)> a.encoding
=> #<Encoding:UTF-8>
irb(main)> a.encode(Encoding::ASCII_8BIT)
Traceback (most recent call last):
        5: from /usr/bin/irb:23:in `<main>'
        4: from /usr/bin/irb:23:in `load'
        3: from /usr/lib/ruby/gems/2.6.0/gems/irb-1.0.0/exe/irb:11:in `<top (required)>'
        2: from (irb):42
        1: from (irb):42:in `encode'
Encoding::InvalidByteSequenceError ("\x8F" on UTF-8)
irb(main)> a.force_encoding(Encoding::ASCII_8BIT)
=> "\x8F"
irb(main):040:0> a.encoding
=> #<Encoding:ASCII-8BIT>

使用 force_encoding 而不是 encode 有什么危险？只是如果我不小心传递了一个多字节字符，它会被转换为多个单字节字符吗？因此，如果确保传递给应用程序的所有字符都在扩展的 ASCII 范围(单字节)内但不安全并且如果将某些 UTF-8 字符传递给应用程序将导致静默转换问题，那么这并不危险。

irb(main):044:0> "\ud087".force_encoding(Encoding::ASCII_8BIT)
=> "\xED\x82\x87"
irb(main):045:0> "\ud087".bytes
=> [237, 130, 135]

---

更新-答案

@mu-is-too-short 的回答和@ForeverZer0 的评论暗示我应该使用 pack 和 unpack 来处理原始字节。

所以与其使用编码和变通方法不如使用它

pattern = 'A' * 2606 + "\x8F\x35\x4A\x5F" + 'C' * 390
pattern.force_encoding(Encoding::ASCII_8BIT)

我应该直接使用bytes

pattern = ['A'.ord] * 2606 + [0x8F, 0x35, 0x4A, 0x5F] + ['C'.ord] * 390
pattern = pattern.pack('C*')

或者这个更容易阅读的语法

pattern = 'A'.bytes * 2606 + "\x8F\x35\x4A\x5F".bytes + 'C'.bytes * 390
pattern = pattern.pack('C*')

Answer 1

无论字节是否为有效的 UTF-8，字符串文字(通常)都是 UTF-8 编码的。因此:

"\x8f".encoding

即使字符串不是有效的 UTF-8，也说 UTF-8。你应该安全地使用 String#force_encoding但是如果你真的想使用原始字节，你可能会更好地使用整数数组并使用 Array#pack将它们混合成字符串:

[ 0x8f, 0x11, 0x06, 0x23, 0xff, 0x00 ].pack('C*')
# "\x8F\x11\x06#\xFF\x00" 
[ 0x8f, 0x11, 0x06, 0x23, 0xff, 0x00 ].pack('C*').encoding
# #<Encoding:ASCII-8BIT> 
[ 0x8f, 0x11, 0x06, 0x23, 0xff, 0x00 ].pack('C*').bytes
# [143, 17, 6, 35, 255, 0] 

结果应该是相同的，但是，IMO，这是明确使用二进制数据(即原始字节)，使您的意图明确，并且应该避免任何编码问题。

还有 String#unpack如果您正在读取的字节存在已知结构并且您想破解它。