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Base64MimeConverter
Last updated at 4:07 am UTC on 11 October 2017
This class encodes and decodes data in Base64 format. This is MIME encoding. We translate a whole stream at once, taking a Stream as input and giving one as output. Returns a whole stream for the caller to use.
           0 A            17 R            34 i            51 z
           1 B            18 S            35 j            52 0
           2 C            19 T            36 k            53 1
           3 D            20 U            37 l            54 2
           4 E            21 V            38 m            55 3
           5 F            22 W            39 n            56 4
           6 G            23 X            40 o            57 5
           7 H            24 Y            41 p            58 6
           8 I            25 Z            42 q            59 7
           9 J            26 a            43 r            60 8
          10 K            27 b            44 s            61 9
          11 L            28 c            45 t            62 +
          12 M            29 d            46 u            63 /
          13 N            30 e            47 v
          14 O            31 f            48 w         (pad) =
          15 P            32 g            49 x
          16 Q            33 h            50 y

Outbound: bytes are broken into 6 bit chunks, and the 0-63 value is converted to a character. 3 data bytes go into 4 characters.
Inbound: Characters are translated in to 0-63 values and shifted into 8 bit bytes.

(See: N. Borenstein, Bellcore, N. Freed, Innosoft, Network Working Group, Request for Comments: RFC 1521, September 1993, MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies. Sec 6.2)

By Ted Kaehler, based on Tim Olson's Base64Filter.

Example

 scriptingSystemImage008
 ^ #'LargeHalo-Collapse' -> (Form fromBinaryStream: (Base64MimeConverter mimeDecodeToBytes: (ReadStream on: self scriptingSystemImageContents008)))

scriptingSystemImageContents008
^ 'iVBORw0KGgoAAAANSUhEUgAAAB4AAAAeBAMAAADJHrORAAAAMFBMVEUyMjLNzYNnZ06YmGU7
OzdTU0OEhF23t3cAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAADpdeSbAAAAEHRSTlP/////////
/wD/////////62q0cgAAANRJREFUeF6FkU0OgkAMhV+GH9cNQVhCNLoVT0CMiVtMZI/GAzjG
C7Dj2LYdICgmdjGZr9OZ6XtF13G0RJTKpoMs5GLgtufU8YCagFYnt3pj9QbkOKoABIUUKK8h
cXBMFAN+XQJbvgA+zmAsJRUMFzBHpX/lt5YlCuUYof62w5mZ6IFcOcaJiLmBVY7gKWd+315p
lKuRgz9sfr73Gv9bMEs/nnLD+Y9+fdcv6wmseBCKHtb7ZL1H1puLXvHjPvVD/LoIWsfq575e
DX7O/P6ex2xe03m+AZecUe0q7jNoAAAAAElFTkSuQmCC'