Ken Raeburn <[EMAIL PROTECTED]> writes: > On Jul 5, 2005, at 18:10, Nic Ferrier wrote: >> Why can't you just pre-parse the data parsed to the base64 decoder? I >> believe that's the correct behaviour. A base64 decoder should decode >> base64, not "base64 but also it does this extra trick if you wave your >> hand in the air" > > Except "this extra trick" is specifically outlined as an option in the > base64 spec (RFC 3548), and MIME invokes that option. So proper "MIME > base64 decoding" would require this extra step of throwing away > characters that are not part of a base64 encoding, and then making a > second pass with the strict base64 decoder. In fact, as I read RFC > 3548 section 2.3, the CR/LF line break sequences in MIME messages are > not part of the base64 alphabet, and therefore > fns.c:IS_BASE64_IGNORABLE already implements a limited form of what > Marc is asking for.
You're quite right - my view of what a base64 decoder should do is based on previous implementation rather than what the spec says (mea culpa). Anyway - 2045 (the last MIME/base64 spec I was aware of) says this: 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 [the acceptable alphabet table] must be ignored by decoding software. In base64 data, characters other than those in Table 1, line breaks, and other white space probably indicate a transmission error, about which a warning message or even a message rejection might be appropriate under some circumstances. So this spec suggests that the base64 decoder should optionally error or throw an exception or call a supplied handler or something. How about I write some advice to just throw unwanted characters away for base64-decode-xx? Different advice could be maybe be used when errors are needed. I'm happy to do this if someone wants it - advice is fairly easy to include in stuff without it necessarily being in Emacs. I'll do it on my train journey to work tommorow morning. Nic _______________________________________________ Emacs-devel mailing list Emacs-devel@gnu.org http://lists.gnu.org/mailman/listinfo/emacs-devel
