Sorry it just doesn’t “feel right”. There are different encoding scheme as laid out in the RFC. and other RFCs <https://en.wikipedia.org/wiki/Base64#Variants_summary_table> that cover their uses.
If you have a system that states “send us Base64 data” it is poorly specified - better to state, send us Base64 data according to RFC 4648 base64url format or according to RFC-2045. In fact, the RFC states: "This encoding may be referred to as "base64url". This encoding should not be regarded as the same as the "base64" encoding and should not be referred to as only "base64". Unless clarified otherwise, "base64" refers to the base 64 in the previous section.” It also states: "If non-alphabet characters are ignored, instead of causing rejection of the entire encoding (as recommended), a covert channel that can be used to "leak" information is made possible." So having a “meta/relaxed decoder” usually leads to specification/interoperability/security problems down the road. I realize that in the “real world” you are often forced to interoperate with these “bad” systems, but as most things in Go, better to be explicit and report errors rather than be clever. > On Feb 2, 2021, at 12:34 PM, 'Axel Wagner' via golang-nuts > <golang-nuts@googlegroups.com> wrote: > > On Tue, Feb 2, 2021 at 6:43 PM Robert Engels <reng...@ix.netcom.com > <mailto:reng...@ix.netcom.com>> wrote: > What “padding” are you referring to? Each must be 2 characters. And there is > a standard that covers this https://tools.ietf.org/html/rfc4648 > <https://tools.ietf.org/html/rfc4648> > > Yes, there indeed is. Section 5 describes a second encoding scheme, used for > URLs and the like. Section 3.2 also talks about the padding I'm referring to > (it's defined elsewhere in the standard) and mentions that, in certain > situations, it can be omitted. In particular, you can omit padding and, in > the decoder, implicitly pad to a multiple of 4 bytes. > > I don't really understand what's the argument is here. The question was if it > is possible to handle all four encoding schemas > <https://golang.org/pkg/encoding/base64/#pkg-variables> supported by the Go > base64 package in one swoop, because as-is, the API requires you to pick one > schema and just see if it returns an error. Roger provided, IMO, a pretty > good answer to that: You can wrap the io.Reader in one that transparently > rewrites any of the four into one well-known one, which can then be handled > by the corresponding decoder. His link provides the code for an > implementation of such a reader. > > >> On Feb 2, 2021, at 10:57 AM, 'Axel Wagner' via golang-nuts >> <golang-nuts@googlegroups.com <mailto:golang-nuts@googlegroups.com>> wrote: >> >> >> Rogers approach seems like the best one to me - wrap the input in a custom >> `io.Reader` that transparently replaces `-_` with `+/` respectively (and >> drop trailing `=`). The bufio approach doesn't work, because there is no >> guarantee that one of the distinguishing characters is early in the stream >> and the "send it to multiple decoders" approach duplicates effort and wastes >> resources. >> >> On Tue, Feb 2, 2021 at 5:43 PM Amnon <amno...@gmail.com >> <mailto:amno...@gmail.com>> wrote: >> Reading through a bufio.Reader is often useful for these situations. >> You can peek the beginning of the input in order to decide which decoder to >> use. >> >> Another option is to use the io.TeeReader to duplicate the reader, >> and then send one copy to each decoder. >> One will succeed, and give you the output. >> But you will need to drain the one that fails to prevent the TeeReader form >> stalling. >> >> >> On Tuesday, 2 February 2021 at 14:17:19 UTC axel.wa...@googlemail.com >> <mailto:axel.wa...@googlemail.com> wrote: >> This question isn't about the decoded data, but about *which* base64 format >> is used - i.e. if it uses padding or not and what 2 characters are used >> outside of a-zA-Z0-9. The most common ones use +/ and -_, so it's easy to >> tell which is used and just accept either (and padding can be viewed as >> optional during decoding anyway). >> >> On Tue, Feb 2, 2021 at 2:37 PM Robert Engels <ren...@ix.netcom.com <>> wrote: >> Base64 is always ASCII. The encoded data may be in an arbitrary format. You >> need to pass additional metadata or try and detect its encoding. >> >>> On Feb 2, 2021, at 6:50 AM, roger peppe <rogp...@gmail.com <>> wrote: >>> >>> >>> In case you find it helpful, here's a clone of the base64 command that I >>> wrote in Go. I did it precisely because I wanted to be able to decode any >>> encoding scheme interchangeably. >>> >>> https://github.com/rogpeppe/misc/blob/master/cmd/base64/base64.go >>> <https://github.com/rogpeppe/misc/blob/master/cmd/base64/base64.go> >>> >>> I agree that it might be useful to have some of this functionality >>> available in the standard library. >>> >>> cheers, >>> rog. >>> >>> On Tue, 2 Feb 2021 at 09:08, hey...@gmail.com <> <hey...@gmail.com <>> >>> wrote: >>> Hi, >>> >>> I have an io.Reader whose content is encoded in base64 with encoding type >>> unknown. Since there shouldn't be any ambiguity between the two, is it >>> possible to make the base64 automatically pick the right one to decode? >>> >>> Currently I have to read everything out to pin down the encoding, which >>> defeats the purpose of using an io.Reader. >>> >>> Is there a solution to this problem? >>> >>> Thanks in advance. >>> >>> >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "golang-nuts" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to golang-nuts...@googlegroups.com <>. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/golang-nuts/0ccee37d-319e-41b3-9bfd-3dc46e0fad78n%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/golang-nuts/0ccee37d-319e-41b3-9bfd-3dc46e0fad78n%40googlegroups.com?utm_medium=email&utm_source=footer>. >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "golang-nuts" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to golang-nuts...@googlegroups.com <>. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/golang-nuts/CAJhgacjkUUSr-dOPFU-W4vG_AXZRY_dYYe2ti-iPuu_XUL%2BNVw%40mail.gmail.com >>> >>> <https://groups.google.com/d/msgid/golang-nuts/CAJhgacjkUUSr-dOPFU-W4vG_AXZRY_dYYe2ti-iPuu_XUL%2BNVw%40mail.gmail.com?utm_medium=email&utm_source=footer>. >> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "golang-nuts" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to golang-nuts...@googlegroups.com <>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/CF76EF37-6F82-42FF-B4D6-4B9FC02F25FC%40ix.netcom.com >> >> <https://groups.google.com/d/msgid/golang-nuts/CF76EF37-6F82-42FF-B4D6-4B9FC02F25FC%40ix.netcom.com?utm_medium=email&utm_source=footer>. >> >> -- >> You received this message because you are subscribed to the Google Groups >> "golang-nuts" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to golang-nuts+unsubscr...@googlegroups.com >> <mailto:golang-nuts+unsubscr...@googlegroups.com>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/44621cb2-fae7-4f40-9e50-35b157f4e838n%40googlegroups.com >> >> <https://groups.google.com/d/msgid/golang-nuts/44621cb2-fae7-4f40-9e50-35b157f4e838n%40googlegroups.com?utm_medium=email&utm_source=footer>. >> >> -- >> You received this message because you are subscribed to the Google Groups >> "golang-nuts" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to golang-nuts+unsubscr...@googlegroups.com >> <mailto:golang-nuts+unsubscr...@googlegroups.com>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/CAEkBMfGGkOX9HzF6e178Cu6BD9Hg4x5LT7AutHkUDPvyK%2BFmYg%40mail.gmail.com >> >> <https://groups.google.com/d/msgid/golang-nuts/CAEkBMfGGkOX9HzF6e178Cu6BD9Hg4x5LT7AutHkUDPvyK%2BFmYg%40mail.gmail.com?utm_medium=email&utm_source=footer>. > > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com > <mailto:golang-nuts+unsubscr...@googlegroups.com>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/CAEkBMfGwDKwoi4TisXPwi0-85%3D_yOqY1AOBw%3DCnH%3D7E4jhJuBg%40mail.gmail.com > > <https://groups.google.com/d/msgid/golang-nuts/CAEkBMfGwDKwoi4TisXPwi0-85%3D_yOqY1AOBw%3DCnH%3D7E4jhJuBg%40mail.gmail.com?utm_medium=email&utm_source=footer>. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. 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