String>>#base64Encoded

>
> On 21 Mar 2011, at 21:52, Stéphane Ducasse wrote:
>
>> On Mar 21, 2011, at 9:42 PM, Sven Van Caekenberghe wrote:
>>
>>> Hi,
>>>
>>> It took me quite some time today to figure this out and it might be relevant for others too:
>>>
>>> it turns out that String>>#base64Encoded introduces newlines which you definitively do not want when doing Basic HTTP Encoding for example. The tricky part is that it works when you stay below a certain length.
>>
>> when would it makes sense?
>
> Base64 encoding ( http://en.wikipedia.org/wiki/Base64 ) is a techique to encode binary data in ASCII strings using a radix 64 representation. It came from the early days of the internet where is was used to encode binary stuff in mail messages (part of MIME encoding). For these usages, line breaks make sense, since some email client break lines themselves, and by preformatting you prevent that, for example:
>
> (Base64MimeConverter
> mimeEncode: (ZnClient get: 'http://www.pharo-project.org/favicon.ico') entity readStream
> multiLine: true) contents
>
> 'AAABAAEAEBAAAAEAIABoBAAAFgAAACgAAAAQAAAAIAAAAAEAIAAAAAAAAAAAABMLAAATCwAA
> AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA0K1+/+2tF//lpRj/0J1F/86x
> kP8AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAADQso7/
> 1Zw1/+ekF//koBf/zZdF/wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
> AAAAAAAAAAAAAAAAAADLrIr/yI05/9SLG//UvKP/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
> AAAAAAAAAAAAAAAA3s2//8qrjf8AAAAAAAAAAAAAAADClmr/28m4/wAAAAAAAAAAAAAAAAAA
> AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACpayz/rH1S/9K9q/8AAAAAAAAAAAAAAAAAAAAA
> AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAxKeP/4lWLv9+Tiz/oXtc/97P
> xf8AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAADYxrj/
> oX1j/2RBNP+QbFT/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
> AAC6m4H/1MGz/+7m4v/Ltqb/tJR3/wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
> AAAAAAAAAAAAAAAAsJWF/1tHVf+qkIH/4tTL/wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
> AAAAAAAAAAAAAAAAAAAAAAAAAAAAANG8rf9GPGj/IiJn/19MYP/Mt6n/AAAAAAAAAAAAAAAA
> AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAANXEuP9NQGj/IiiB/youf/8NFnb/Qztx/9PC
> t/8AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAADczcL/mIGA/y8ziP8nMZj/
> GSGF/4l2hP/Tw7n/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAMy4
> q/8pMZj/JzKi/yUxov+znJb/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
> AAAAAAAAAADezsT/d3Om/1dt0f9cZrz/v6mf/wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
> AAAAAAAAAAAAAAAAAAAAAAAAAAAAAJqapP+i3f//iazZ/9/Pwv8AAAAAAAAAAAAAAAAAAAAA
> AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAADBqIv/lYps/7Caev8AAAAAAAAAAAAA
> AAAAAAAA/g8AAP8H8L//wwAA/nMAAP8fNcL/BwAA/4cAAP8HAAD/DwAA/wc4FP4DAAD+AwAA
> /wf///8H////hzp0/48AAA=='
>
> Base64 encoding is also used a lot in cryptography to encode binary data like hashes or even for silly obfuscation. For example, in HTTP, Basic Authentication is a defined as a HTTP header called 'Authorization' with as value 'Basic' <space> <credentials> where credentials is obtained by Base64 encoding <username>:<password>.
>
> ZnRequest>>#setBasicAuthenticationUsername: username password: password
> self headers
> at: 'Authorization'
> put: 'Basic ', (ZnUtils encodeBase64: (username, ':', password))
>
> ZnUtils class>>#encodeBase64: string
> ^ (Base64MimeConverter mimeEncode: string readStream multiLine: false) contents
>
> Here you don't want line breaks since it would break the common assumption that a header is a single line (technically, multiline headers do exist, but that is another story).
>
> Now, as long as the input string is below 55 characters in length, no line breaks will be introduced. In code (assuming no line line breaks will be introduced by our email clients or the mailing list software inbetween; re-execute in a workspace if necessary):
>
> (Base64MimeConverter
> mimeEncode: ((String new: 54) atAllPut: $A) readStream
> multiLine: true) contents
>
> 'QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB'
>
> (Base64MimeConverter
> mimeEncode: ((String new: 54) atAllPut: $A) readStream
> multiLine: false) contents
>
> 'QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB'
>
> (Base64MimeConverter
> mimeEncode: ((String new: 55) atAllPut: $A) readStream
> multiLine: true) contents
>
> 'QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB
> QQ=='
>
> (Base64MimeConverter
> mimeEncode: ((String new: 55) atAllPut: $A) readStream
> multiLine: false) contents
>
> 'QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQQ=='
>
> Please note, this is not a bug, just a gotcha that can go unnoticed for quite some time.
>
> Sven
>
> PS: Base64 decoding is clever enough to transparently deal with line breaks.
>
>>> This can easily be solved by invoking Base64MimeConvertor with the #mimeEncode: <string> multiLine: false
>>>
>>> Zinc HTTP Components now does this consistently through ZnUtils class>>#encodeBase64:
>>>
>>> Sven
>
>