function
|
Library: Base 64 (OMFFBASE64)
Import : omffbase64.xmd |
Returns: a scannable input source for streaming data |
export external string source function reader from value string source input-data
Use base64.reader to read its value string source input-data argument, and
return the binary data converted from a Base 64 encoding to raw binary octets. That is, the provided data is in
Base 64, but the program sees binary data.
Any input data not recognized as part of a Base 64 encoding is ignored, so this library should not be used to validate Base 64 encoding.
The function read-attachment () below reads as much Base 64 as can be found in its string
source argument, passes it through base64.reader, thereby converting it from Base 64 to raw binary data,
and emits the raw data on its #current-output.
import "omffbase64.xmd" prefixed by base64. define string source function read-attachment (value string source s) as output base64.reader from (s take [letter | digit | "+/=%10#%13#"]+)
Base 64 data can be padded with one or two = characters when the original binary data is not a
multiple of three bytes. When base64.reader is used to decode such a padded string, the trailing
bytes are mapped to null bytes. If these trailing null bytes are undesired, they can be removed by using pattern
matching, as in
output (omffbase64.reader from #current-input) take any ++ lookahead ("%0#"* value-end)
To use base64.reader, you must import OMFFBASE64 into your program using an
import declaration such as:
import "omffbase64.xmd" prefixed by base64.