base64编码长度参数 [英] base64 encode length parameter

问题描述

我正在解码base64字符串，对其进行修改，然后使用Ruby重新对其进行编码.我重新编码时的问题是，ruby编码库在60个左右的字符后添加了换行符.如何告诉我每行没有最大字符数?

I am decoding a base64 string, modifying it, and re-encoding it with Ruby. The problem when I re-encode it is that the ruby encode library is adding a linebreak after 60 or so characters. How can I tell it to not have max characters per line limit?

val = "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"

decoded_val = Base64.decode64(val)
encoded_val = Base64.encode64(val)

#=> QmFzZTY0IGlzIGEgZ2VuZXJpYyB0ZXJtIGZvciBhIG51bWJlciBvZiBzaW1p
#   bGFyIGVuY29kaW5nIHNjaGVtZXMgdGhhdCBlbmNvZGUgYmluYXJ5IGRhdGEg
#   YnkgdHJlYXRpbmcgaXQgbnVtZXJpY2FsbHkgYW5kIHRyYW5zbGF0aW5nIGl0
#   IGludG8gYSBiYXNlIDY0IHJlcHJlc2VudGF0aW9uLiBUaGUgQmFzZTY0IHRl
#   cm0gb3JpZ2luYXRlcyBmcm9tIGEgc3BlY2lmaWMgTUlNRSBjb250ZW50IHRy
#   YW5zZmVyIGVuY29kaW5nLg0KDQpCYXNlNjQgZW5jb2Rpbmcgc2NoZW1lcyBh
#   cmUgY29tbW9ubHkgdXNlZCB3aGVuIHRoZXJlIGlzIGEgbmVlZCB0byBlbmNv
#   ZGUgYmluYXJ5IGRhdGEgdGhhdCBuZWVkcyBiZSBzdG9yZWQgYW5kIHRyYW5z
#   ZmVycmVkIG92ZXIgbWVkaWEgdGhhdCBhcmUgZGVzaWduZWQgdG8gZGVhbCB3
#   aXRoIHRleHR1YWwgZGF0YS4gVGhpcyBpcyB0byBlbnN1cmUgdGhhdCB0aGUg
#   ZGF0YSByZW1haW5zIGludGFjdCB3aXRob3V0IG1vZGlmaWNhdGlvbiBkdXJp
#   bmcgdHJhbnNwb3J0LiBCYXNlNjQgaXMgdXNlZCBjb21tb25seSBpbiBhIG51
#   bWJlciBvZiBhcHBsaWNhdGlvbnMgaW5jbHVkaW5nIGVtYWlsIHZpYSBNSU1F
#   LCBhbmQgc3RvcmluZyBjb21wbGV4IGRhdGEgaW4gWE1MLg==

推荐答案

RFC 4648:Base16，Base32和Base64数据编码的意思是:

3.3.编码数据中非字母字符的解释
[...]
实现必须拒绝编码后的数据(如果包含) 解释基本编码时基本字母之外的字符 数据，除非规范中明确引用此文档 另有规定.此类规范可能改为MIME 这样做，基本编码字母之外的字符应 只是在解释数据时被忽略(对您的内容放任自流 接受").请注意，这意味着任何相邻的回车/ 换行(CRLF)字符构成非字母字符"，并且 被忽略.

3.3. Interpretation of Non-Alphabet Characters in Encoded Data
[...]
Implementations MUST reject the encoded data if it contains characters outside the base alphabet when interpreting base-encoded data, unless the specification referring to this document explicitly states otherwise. Such specifications may instead state, as MIME does, that characters outside the base encoding alphabet should simply be ignored when interpreting data ("be liberal in what you accept"). Note that this means that any adjacent carriage return/ line feed (CRLF) characters constitute "non-alphabet characters" and are ignored.

因此换行符很好，即使它们不严格符合RFC 4648，几乎所有内容都将忽略它们.

So the newlines are fine and pretty much everything will ignore them even if they're not strictly compliant with RFC 4648.

此外，精细手册这么说:

encode64(bin)

返回bin的Base64编码版本.此方法符合RFC2045.每60个编码的字符都会添加换行符[sic].

Returns the Base64-encoded version of bin. This method complies with RFC 2045. Line feeds are added to every 60 encoded charactors [sic].

所以60个字符的行长度是有意的并且是指定的.如果您想要严格的RFC 4648 Base64(即没有换行符)，则有

So the 60 character line length is intentional and specified. If you want strict RFC 4648 Base64 (i.e. no newlines), then there is strict_encode64:

strict_encode64(bin)

返回bin的Base64编码版本.此方法符合RFC4648.不添加换行符.

Returns the Base64-encoded version of bin. This method complies with RFC 4648. No line feeds are added.

所以您可以说Base64.strict_encode64(val)来获取所需的输出.

So you can say Base64.strict_encode64(val) to get the output you're looking for.

作为参考，这是RFC 2045的相关部分:

And for reference, here's the relevant section of RFC 2045:

6.8. Base64内容传输编码
[...]
编码后的输出流必须不再以行表示 每个超过76个字符.所有换行符或其他字符都没有 表1中发现的错误必须由解码软件忽略.

6.8. Base64 Content-Transfer-Encoding
[...]
The encoded output stream must be represented in lines of no more than 76 characters each. All line breaks or other characters not found in Table 1 must be ignored by decoding software.

所以60个字符的行长多少有些随意，但自60 < 76起符合RFC 2045.

So the 60 character line length is somewhat arbitrary but compliant with RFC 2045 since 60 < 76.

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