URL-safe base64 decoding for R

Question

I don't know if it's just R being notoriously hard to search for but I can't seem to find a URL-safe base64 decoder for R.

Does anyone know of one ?

Edit I've used various decoders, the RCurl::base64decode() function as well as online ones and the results are somewhat inconsistent.

I admit I don't understand the full details of what differentiates a "URL-safe" base64 decoder but find it dismissive to have my question closed in a matter of minutes due to a moderator's misunderstanding of what I'm asking before anyone gets a chance to answer.

Edit 2 The equivalent in Python is base64.urlsafe_b64decode(s), and as yet noone has implemented this in R.

Using library(sos) as recommended in the comments brings up 3 packages, and as expected a Google search would have found them had they URL-safe methods.

base64::decode() has just two parameters, input and output, i.e. only works on files, and attempting this on my string produces a mangled output. The only other methods in the package are encode() and img (for image file base64-string encoding)
base64enc::base64decode() follows much the same, though can use a text connection rather than solely a file input. Again, no option to use a modified URL-safe alphabet
RCurl::base64Decode() can only take text input (befitting a stream-handling package), and a mode parameter can be set to either raw or character. It doesn't seem that either mode permits altering the decoding alphabet.

The Python docs explain that a URL-safe alphabet

substitutes - instead of + and _ instead of / in the standard Base64 alphabet.

I'd be interested to know how to use a custom alphabet. If I understand correctly the 'raw' mode has already applied the alphabet, and thus mistranslated.

The example above is the body of an email I retrieved through the Gmail API, which base64-encodes with such a URL-safe encoder:

PGRpdiBkaXI9Imx0ciI-SGksPGJyPjxicj5JIGNhbiYjMzk7dCBpbnN0YWxsIHhwcyBiZWNhdXNlIGR1cmluZyBjb21waWxlIEkgZ2V0OjxkaXY-PGJyPjwvZGl2PjxkaXY-PGZvbnQgZmFjZT0ibW9ub3NwYWNlLCBtb25vc3BhY2UiPlRNTE1hdGguY3h4OjUxOjE5OiBmYXRhbCBlcnJvcjogVE1hdGguaDogTm8gc3VjaCBmaWxlIG9yIGRpcmVjdG9yeTxicj48L2ZvbnQ-PC9kaXY-PGRpdj48Zm9udCBmYWNlPSJtb25vc3BhY2UsIG1vbm9zcGFjZSI-PGJyPjwvZm9udD48L2Rpdj48ZGl2PjxkaXY-PGZvbnQgZmFjZT0ibW9ub3NwYWNlLCBtb25vc3BhY2UiPsKgI2luY2x1ZGUgJnF1b3Q7VE1hdGguaCZxdW90OzwvZm9udD48L2Rpdj48ZGl2Pjxmb250IGZhY2U9Im1vbm9zcGFjZSwgbW9ub3NwYWNlIj7CoCDCoCDCoCDCoCDCoCDCoCDCoCDCoCDCoCDCoF48L2ZvbnQ-PC9kaXY-PGRpdj48Zm9udCBmYWNlPSJtb25vc3BhY2UsIG1vbm9zcGFjZSI-Y29tcGlsYXRpb24gdGVybWluYXRlZC48L2ZvbnQ-PC9kaXY-PGRpdj48Zm9udCBmYWNlPSJtb25vc3BhY2UsIG1vbm9zcGFjZSI-bWFrZTogKioqIFtUTUxNYXRoLm9dIEVycm9yIDE8L2ZvbnQ-PC9kaXY-PGRpdj48Zm9udCBmYWNlPSJtb25vc3BhY2UsIG1vbm9zcGFjZSI-RVJST1I6IGNvbXBpbGF0aW9uIGZhaWxlZCBmb3IgcGFja2FnZSDigJh4cHPigJk8L2ZvbnQ-PC9kaXY-PC9kaXY-PGRpdj48YnI-PGZvbnQgZmFjZT0iYXJpYWwsIGhlbHZldGljYSwgc2Fucy1zZXJpZiI-RG8geW91IGhhdmUgYW55IGlkZWEgd2hlcmUgSSYjMzk7dmUgZ29uZSB3cm9uZywgb3IgaG93IEkgbWlnaHQgZml4IGl0PyBGdXJ0aGVyIGRldGFpbHMgb2YgaG93IEkgd2VudCBhYm91dCBpdCBhcmUgPGEgaHJlZj0iaHR0cHM6Ly9naXRodWIuY29tL2xtbXgvZGV2bm90ZXMvd2lraS9JbnN0YWxsaW5nLUNFUk4mIzM5O3MtUk9PVC1mcmFtZXdvcmsiPmhlcmU8L2E-wqBhbmQgZnVsbCBzY3JlZW5zaG90IGF0dGFjaGVkLjwvZm9udD48L2Rpdj48ZGl2Pjxmb250IGZhY2U9ImFyaWFsLCBoZWx2ZXRpY2EsIHNhbnMtc2VyaWYiPjxicj48L2ZvbnQ-PC9kaXY-PGRpdj48Zm9udCBmYWNlPSJhcmlhbCwgaGVsdmV0aWNhLCBzYW5zLXNlcmlmIj5JIHRyaWVkIG1hbnVhbGx5IGFkZGluZyBpbiB0aGUgZmlsZXMgdGhlIGVycm9yIG1lc3NhZ2Ugc2FpZCB3ZXJlIG1pc3NpbmcsIGJ1dCBldmVudHVhbGx5IGl0IGdhdmUgYSBkaWZmZXJlbnQga2luZCBvZiBlcnJvciBhbmQgSSBkZWxldGVkIHRoZXNlIGFkZGl0aW9uYWwgZmlsZXMgYWdhaW4gKHNlZSB0aGUgbGluayBhYm92ZSkuPC9mb250PjwvZGl2PjxkaXY-PGZvbnQgZmFjZT0iYXJpYWwsIGhlbHZldGljYSwgc2Fucy1zZXJpZiI-PGJyPjwvZm9udD48L2Rpdj48ZGl2Pjxmb250IGZhY2U9ImFyaWFsLCBoZWx2ZXRpY2EsIHNhbnMtc2VyaWYiPkkgaG9wZSB5b3UgbWF5IGJlIGFibGUgdG8gYWR2aXNlLCBJJiMzOTt2ZSBydW4gb3V0IG9mIGlkZWFzIGFuZCBleHBlcnRpc2Ugb24gaG93IGVsc2UgdG8gcHJvY2VlZC48L2ZvbnQ-PC9kaXY-PGRpdj48Zm9udCBmYWNlPSJhcmlhbCwgaGVsdmV0aWNhLCBzYW5zLXNlcmlmIj48YnI-PC9mb250PjwvZGl2PjxkaXY-PGZvbnQgZmFjZT0iYXJpYWwsIGhlbHZldGljYSwgc2Fucy1zZXJpZiI-QmVzdCB3aXNoZXMsPC9mb250PjwvZGl2PjxkaXY-PGZvbnQgZmFjZT0iYXJpYWwsIGhlbHZldGljYSwgc2Fucy1zZXJpZiI-PGJyPjwvZm9udD48L2Rpdj48ZGl2Pjxmb250IGZhY2U9ImFyaWFsLCBoZWx2ZXRpY2EsIHNhbnMtc2VyaWYiPkxvdWlzPC9mb250PjwvZGl2PjwvZGl2Pg0K

which an online URL-safe decoder will give as

Hi,

I can't install xps because during compile I get:

TMLMath.cxx:51:19: fatal error: TMath.h: No such file or directory

#include "TMath.h"
^
compilation terminated.
make: *** [TMLMath.o] Error 1
ERROR: compilation failed for package ‘xps’

Do you have any idea where I've gone wrong, or how I might fix it? Further details of how I went about it are here and full screenshot attached.

I tried manually adding in the files the error message said were missing, but eventually it gave a different kind of error and I deleted these additional files again (see the link above).

I hope you may be able to advise, I've run out of ideas and expertise on how else to proceed.

Best wishes,

Louis

The RCurl function gives a truncated and patchy decoding:

I can't install xps because during compile I get:
TMLMath.cxx:51:19: fatal error: TMath.h: No such file or directory
#include "TMath.h"
^<\001\x89\xc8https://github.com/lmmx/devnotes/wiki/Installing-CERN's-ROOT-framework\">here<

While the online base64 decoder I was using won't decode it at all, reporting an error.

I'll have to write something to use a custom alphabet myself if noone knows a way to do this with existing R packages. I'd prefer not to have to invoke Python, if possible.

Louis Maddox · Accepted Answer

Well... that was embarrassingly easy.

base64Decode(gsub("-","+",gsub("/","_",strtodecode)))

Sorry to answer my own question, it seems way more complicated than it is

Edit this actually has to be base64Decode(gsub("-","+",gsub("_","/",strtodecode))) for the case I'm working on, but for an example the above worked - there are multiple base64 alphabets.

URL-safe base64 decoding for R

Answers (1)

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