cppcms::b64url compatibility

[masaoliou]

I have tested on https://dogmamix.com/MimeHeadersDecoder and https://www.base64encode.org and have found that cppcms::b64url::encode() seems to be incompatible with https://datatracker.ietf.org/doc/html/rfc2047.txt

This implementation works as expected.

Any idea?

[artyom-beilis]

Can you please be more specific. What exactly does not compatible?

Can you show an example of what b64url creates and what do you expect?

[masaoliou]

#include <cppcms/base64.h>
#include <sstream>
#include <iostream>

int main()
{
    const std::string s("This is John Smith.");
    std::ostringstream os;
    cppcms::b64url::encode(reinterpret_cast<const unsigned char*>(s.c_str()),reinterpret_cast<const unsigned char*>(s.c_str())+s.size(),os);
    std::cout << os.str() << std::endl; //VGhpcyBpcyBKb2huIFNtaXRoLg
    std::cout << "=?utf-8?B?" << os.str() << "?=" << std::endl; //=?utf-8?B?VGhpcyBpcyBKb2huIFNtaXRoLg?=
    return 0;
}

This web page can't decode the last string =?utf-8?B?VGhpcyBpcyBKb2huIFNtaXRoLg?= following "Subject: ".

The following shell command

echo -ne "This is John Smith." | base64

gives the following string:

VGhpcyBpcyBKb2huIFNtaXRoLg==

The aforementioned web page properly decodes the following string after "Subject: ":

=?utf-8?B?VGhpcyBpcyBKb2huIFNtaXRoLg==?=

[artyom-beilis]

I explain, there is difference between base64 and base64url

https://en.wikipedia.org/wiki/Base64#Variants_summary_table

Short summary:

• Base 64 uses + and / characters while base64url uses - and _
• Base64url does not require padding with = and does not require new lines

You are confusing two very similar but different encodings - the code you linked to is actually base64 and not base64url.