.TH LIBAR2_DECODE_BASE64 3 LIBAR2
.SH NAME
libar2_decode_base64 - Decode base64-encoded data

.SH SYNOPSIS
.nf
#include <libar2.h>

size_t libar2_decode_base64(const char *\fIstr\fP, void *\fIdata\fP, size_t *\fIlenp\fP);
.fi
.PP
Link with
.IR -lar2 .

.SH DESCRIPTION
The
.BR libar2_decode_base64 ()
function decodes some binary data that has
been encoded with base64. The base64-encoding
shall be provided via the
.I str
parameter, and is decoded into the
.I data
parameter
(unless
.I data
is
.IR NULL ).
The length of the decoded data, in bytes,
is stored in
.IR *lenp .
.PP
.I str
may, but does not have to, be padded, up to
(or short there of) the next length that is
divisible by 4, unless the length is already
divisible by 4, using equals-sign
.RB ( = )
characters.
.PP
Decoding stops at the first byte in
.I str
that cannot be part of a valid base64-encoding.
.PP
.I str
and
.I lenp
may not be
.IR NULL .

.SH RETURN VALUES
The
.BR libar2_decode_base64 ()
function returns the number of bytes
successfully decoded from
.I str
(that is, the number of bytes read (minus
any byte determined not to be part of the
encoded data), not the number of bytes
stored in
.IR data ),
and stores the decoded data in
.I data
and the length of the data, after it has
been decoded, in
.IR *lenp .

.SH ERRORS
The
.BR libar2_decode_base64 ()
function cannot fail.

.SH EXAMPLES
The following example demonstrates how to
decode data from base64 and store it in a
dynamically allocated buffer.
.PP
.nf
#include <libar2.h>
#include <stdlib.h>

static char *
decode_base64(const const *str, char **endp, size_t *lenp)
{
    size_t len;
    size_t n = libar2_decode_base64(str, NULL, &len);
    char *data = len ? malloc(len) : NULL;
    if (len && !data) {
        *endp = NULL;
        return NULL;
    }
    if (libar2_decode_base64(str, data, lenp) != n || *lenp != len)
        abort();
    *endp = &str[n];
    return data;
}
.fi

.SH NOTES
The encoding specified for
.BR crypt (3)
is B64, which is similar to, but with significant
differences from, base64, which is the encoding
that is standardised for Argon2.

.SH SEE ALSO
.BR libar2 (7),
.BR libar2_encode_base64 (3)