Extensions to the `base64' Program

[Matt Walker]

Dear coreutils Development Team,

I recently ran into a problem when using the base64 program to decode strings received from the GMail API.  Here is a relevant Stack Overflow post:

http://stackoverflow.com/questions/24812139/base64-decoding-of-mime-email-not-working-gmail-api

And here is a trouble string:

IFN0YXkgbW9yZSBvcmdhbml6ZWQgd2l0aCBHbWFpbCdzIGluYm94DQpbaW1hZ2U6IEdvb2dsZV0NCg0KSGkgTWF0dA0KDQpHbWFpbCdzIGluYm94IHB1dHMgeW91IGluIGNvbnRyb2wNCg0KW2ltYWdlOiBJbmJveCB2aWRlb10gPGh0dHBzOi8vd3d3LnlvdXR1YmUuY29tL3dhdGNoP3Y9Q0ZmN2RsZXdKdXM-DQpNZWV0IHRoZSBpbmJveA0KDQpHbWFpbCdzIGluYm94IHNvcnRzIHlvdXIgZW1haWwgaW50byBjYXRlZ29yaWVzIHNvIHlvdSBjYW4gc2VlIHdoYXQncyBuZXcgYXQNCmEgZ2xhbmNlLCBkZWNpZGUgd2hpY2ggZW1haWxzIHlvdSB3YW50IHRvIHJlYWQgd2hlbiBhbmQgdmlldyBzaW1pbGFyIHR5cGVzDQpvZiBlbWFpbHMgdG9nZXRoZXIuIFdhdGNoIHRoZSB2aWRlbw0KPGh0dHBzOi8vd3d3LnlvdXR1YmUuY29tL3dhdGNoP3Y9Q0ZmN2RsZXdKdXM-DQpbaW1hZ2U6IFNvY2lhbCB0YWJdDQpDaG9vc2UgeW91ciBjYXRlZ29yaWVzDQoNClRoZSBTb2NpYWwgYW5kIFByb21vdGlvbnMgY2F0ZWdvcmllcyBhcmUgb24gYnkgZGVmYXVsdC4gQWRkIGNhdGVnb3JpZXMgbGlrZQ0KVXBkYXRlcyBhbmQgRm9ydW1zIG9yIHJlbW92ZSBjYXRlZ29yaWVzIHRvIGhhdmUgdGhvc2UgZW1haWxzIHNob3cgdXAgaW4NCnlvdXIgUHJpbWFyeSBpbmJveC4gTGVhcm4gaG93IHRvIGNob29zZSBjYXRlZ29yaWVzDQo8aHR0cHM6Ly9zdXBwb3J0Lmdvb2dsZS5jb20vbWFpbC8_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_dj1DRmY3ZGxld0p1cyZhbXA-Lg0KDQoNCltpbWFnZTogR21haWwgaWNvbl1IYXBweSBlbWFpbGluZywNClRoZSBHbWFpbCBUZWFtDQrCqSAyMDE1IEdvb2dsZSBJbmMuIDE2MDAgQW1waGl0aGVhdHJlIFBhcmt3YXksIE1vdW50YWluIFZpZXcsIENBIDk0MDQzDQo=

The problem is that `base64' doesn't support the RFC 4648 standard.  An obvious work around is to do something akin to "cat <file> | sed 's/-/+/' | sed 's|_|/|' | base64 --decode" or whatever (forgive the double sed please).  However, it would be more GNU-y I think to support the "web" or "url-safe" version of Base64 encoding directly in the program as an extension.

If nobody feels like doing it, I could probably tackle the problem.  I just want to ensure people want this first.

Some follow up thoughts if the change is deemed acceptable: should decode try to be "smart" and decode according to the first decoding that makes sense, or should there possibly be a "--smart-decode" option, or should we just have "--encoding=web" or whatever and call it a day?

Sincerely,

Matt Walker