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.\" Author: Archie Cobbs <archie@freebsd.org>
.\"
.\" $Id: base64.3,v 1.1.1.1 2012/02/21 23:25:53 misho Exp $
.\"
.Dd April 22, 2002
.Dt BASE64 3
.Os
.Sh NAME
.Nm b64_encoder_create ,
.Nm b64_decoder_create
.Nd base-64 encoder and decoder
.Sh LIBRARY
PDEL Library (libpdel, \-lpdel)
.Sh SYNOPSIS
.In pdel/io/filter.h
.In pdel/io/base64.h
.Ft "struct filter *"
.Fn b64_encoder_create "const char *charset"
.Ft "struct filter *"
.Fn b64_decoder_create "const char *charset" "int strict"
.Vt extern const char "b64_rfc2045_charset[]" ;
.Sh DESCRIPTION
These routines create filter objects (see
.Xr filter 3)
that encode and decode binary data using base-64 encoding.
.Pp
Both functions take a
.Fa charset
argument.
If equal to
.Dv NULL ,
then the default (RFC 2045) character set is used.
Otherwise,
.Fa charset
must point to a string with 65 unique characters.
The first 64 are used to encode the data, while the last character is used
as a pad character when the data length is not a multiple of three.
.Pp
.Fn b64_encoder_create
returns a new encoding filter.
For every three bytes input to the filter, four bytes from the chosen
character set will be output.
If the input length is not a multiple of three, then one or two pad
characters will be added at the end of the output, so that the output
length of the filter is always a multiple of four.
.Pp
.Fn b64_decoder_create
returns a new decoding filter.
Every four bytes input to the filter are decoded into up to three bytes
of output.
If
.Fa strict
is non-zero, then any malformed input causes an internal error to be
generated in the filter, with
.Va errno
set to
.Er EINVAL.
Malformed input is any input character not from the chosen character set.
In any case, the pad character is always ignored.
If
.Fa strict
is zero, then any unrecognized characters are simply ignored, rather than
causing an error.
.Pp
.Fn b64_encoder_create
always generates strings that are accepted by
.Fn b64_decoder_create
in strict mode, when created with the same character set.
.Pp
The RFC 2045 character set is avilable in
.Va b64_rfc2045_charset .
.Sh RETURN VALUES
If there was a system error,
.Fn b64_encoder_create
and
.Fn b64_encoder_create
return
.Dv NULL
with
.Va errno
set to the appropriate value.
If an invalid
.Fa charset
is passed,
.Va errno
will be set to
.Er EINVAL.
.Sh SEE ALSO
.Xr filter 3 ,
.Xr libpdel 3
.Rs
.%A N. Freed
.%A N. Borenstein
.%T "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies"
.%O RFC 2045
.Re
.Sh HISTORY
The PDEL library was developed at Packet Design, LLC.
.Dv "http://www.packetdesign.com/"
.Sh AUTHORS
.An Archie Cobbs Aq archie@freebsd.org