base64 encode length parameter

Question

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==

Answer 1

RFC 4648: The Base16, Base32, and Base64 Data Encodings has this to say:

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.

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

Also, the fine manual has this to say:

encode64(bin)

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

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)

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

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

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

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.

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