Base64 decode data

From Rosetta Code
Base64 decode data is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

See Base64 encode data.

Now write a program that takes the output of the Base64 encode data task as input and regenerate the original file.

When working on the VBA implementation I found several 'solutions' on the net, including one from the software maker himself, that showed output with incorrect padding. Obviously with incorrect padding in the output you can not decode correctly to the original file again.

Go[edit]

As images can no longer be uploaded to RC, I've encoded and decoded a string rather than the Rosetta Code icon.

package main
 
import (
"encoding/base64"
"fmt"
)
 
func main() {
msg := "Rosetta Code Base64 decode data task"
fmt.Println("Original :", msg)
encoded := base64.StdEncoding.EncodeToString([]byte(msg))
fmt.Println("\nEncoded  :", encoded)
decoded, err := base64.StdEncoding.DecodeString(encoded)
if err != nil {
fmt.Println(err)
return
}
fmt.Println("\nDecoded  :", string(decoded))
}
Output:
Original : Rosetta Code Base64 decode data task

Encoded  : Um9zZXR0YSBDb2RlIEJhc2U2NCBkZWNvZGUgZGF0YSB0YXNr

Decoded  : Rosetta Code Base64 decode data task

Perl[edit]

The MIME::Base64 module is to be preferred, but this works too.

sub decode_base64 {
my($d) = @_;
$d =~ tr!A-Za-z0-9+/!!cd;
$d =~ s/=+$//;
$d =~ tr!A-Za-z0-9+/! -_!;
my $r = '';
while( $d =~ /(.{1,60})/gs ){
my $len = chr(32 + length($1)*3/4);
$r .= unpack("u", $len . $1 );
}
$r;
}
 
$data = <<EOD;
J1R3YXMgYnJpbGxpZywgYW5kIHRoZSBzbGl0aHkgdG92ZXMKRGlkIGd5cmUgYW5kIGdpbWJsZSBp
biB0aGUgd2FiZToKQWxsIG1pbXN5IHdlcmUgdGhlIGJvcm9nb3ZlcywKQW5kIHRoZSBtb21lIHJh
dGhzIG91dGdyYWJlLgo=
EOD

 
print decode_base64($data) . "\n";
Output:
'Twas brillig, and the slithy toves
Did gyre and gimble in the wabe:
All mimsy were the borogoves,
And the mome raths outgrabe.

Perl 6[edit]

Works with: Rakudo version 2018.11
my $e64 = '
VG8gZXJyIGlzIGh1bWFuLCBidXQgdG8gcmVhbGx5IGZvdWwgdGhpbmdzIHVwIHlvdSBuZWVkIGEgY2
9tcHV0ZXIuCiAgICAtLSBQYXVsIFIuIEVocmxpY2g=
'
;
 
my @base64map = flat 'A' .. 'Z', 'a' .. 'z', ^10, '+', '/';
my %base64 is default(0) = @base64map.pairs.invert;
 
sub base64-decode-slow ($enc) {
my $buf = Buf.new;
for $enc.subst(/\s/, '', :g).comb(4) -> $chunck {
$buf.append: |(sprintf "%06d%06d%06d%06d", |$chunck.comb.map:
{%base64{$_}.base(2)}).comb(8).map: {:2($_)};
}
$buf
}
 
say 'Slow:';
say base64-decode-slow($e64).decode('utf8');
 
 
# Of course, the above routine is slow and is only for demonstration purposes.
# For real code you should use a module, which is MUCH faster and heavily tested.
say "\nFast:";
use Base64::Native;
say base64-decode($e64).decode('utf8');
Output:
Slow:
To err is human, but to really foul things up you need a computer.
    -- Paul R. Ehrlich

Fast:
To err is human, but to really foul things up you need a computer.
    -- Paul R. Ehrlich

Phix[edit]

include builtins\base64.e
string s = "Rosetta Code Base64 decode data task"
string e = encode_base64(s)
?e
?decode_base64(e)
Output:
"Um9zZXR0YSBDb2RlIEJhc2U2NCBkZWNvZGUgZGF0YSB0YXNr"
"Rosetta Code Base64 decode data task"

Ruby[edit]

require 'base64'
 
perl6_example ='
VG8gZXJyIGlzIGh1bWFuLCBidXQgdG8gcmVhbGx5IGZvdWwgdGhpbmdzIHVwIHlvdSBuZWVkIGEgY2
9tcHV0ZXIuCiAgICAtLSBQYXVsIFIuIEVocmxpY2g=
'

puts Base64.decode64 perl6_example
Output:
To err is human, but to really foul things up you need a computer.
    -- Paul R. Ehrlich

Sidef[edit]

var data = <<'EOT'
VG8gZXJyIGlzIGh1bWFuLCBidXQgdG8gcmVhbGx5IGZvdWwgdGhpbmdzIHVwIHlvdSBuZWVkIGEgY2
9tcHV0ZXIuCiAgICAtLSBQYXVsIFIuIEVocmxpY2g=
EOT
 
say data.decode_base64
Output:
To err is human, but to really foul things up you need a computer.
    -- Paul R. Ehrlich

zkl[edit]

Using shared libraries for cURL and message hashing:

var [const] MsgHash=Import("zklMsgHash"), Curl=Import("zklCurl");
 
icon:=Curl().get("http://rosettacode.org/favicon.ico"); //-->(Data(4,331),693,0)
icon=icon[0][icon[1],*]; // remove header
iconEncoded:=MsgHash.base64encode(icon);
iconDecoded:=MsgHash.base64decode(iconEncoded);
File("rosettaCodeIcon.ico","wb").write(iconDecoded); # eyeball checking says good
println("Is the Rosetta Code icon the same (byte for byte) encoded then decoded: ",
icon==iconDecoded);
Output:
Is the Rosetta Code icon the same (byte for byte) encoded then decoded: True
Text based test:
msg,b64 := "Rosetta Code Base64 decode data task", MsgHash.base64encode(msg);
println("Original: %s\nEncoded:  %s\nBytes:  %s\nDecoded:  %s"
.fmt(msg, b64.text, b64.bytes().apply("toString",16).concat(","),
MsgHash.base64decode(b64).text));
Original: Rosetta Code Base64 decode data task
Encoded:  Um9zZXR0YSBDb2RlIEJhc2U2NCBkZWNvZGUgZGF0YSB0YXNr

Bytes:    55,6d,39,7a,5a,58,52,30,59,53,42,44,62,32,52,6c,49,45,4a,68,63,32,55,32,4e,43,42,6b,5a,57,4e,76,5a,47,55,67,5a,47,46,30,59,53,42,30,59,58,4e,72,a
Decoded:  Rosetta Code Base64 decode data task