openssl/doc/man3/BIO_f_base64.pod

=pod

=head1 NAME

BIO_f_base64 - base64 BIO filter

=head1 SYNOPSIS

=for openssl multiple includes

 #include <openssl/bio.h>
 #include <openssl/evp.h>

 const BIO_METHOD *BIO_f_base64(void);

=head1 DESCRIPTION

BIO_f_base64() returns the base64 BIO method. This is a filter
BIO that base64 encodes any data written through it and decodes
any data read through it.

Base64 BIOs do not support BIO_gets() or BIO_puts().

For writing, by default output is divided to lines of length 64
characters and there is a newline at the end of output.
This behavior can be changed with B<BIO_FLAGS_BASE64_NO_NL> flag.

For reading, the first line of base64 content should be at most 1024 bytes long
including newline unless the flag B<BIO_FLAGS_BASE64_NO_NL> is set.
Subsequent input lines can be of any length (i.e., newlines may appear anywhere
in the input) and a newline at the end of input is not needed.

Also when reading, unless the flag B<BIO_FLAGS_BASE64_NO_NL> is set, initial
lines that contain non-base64 content (whitespace is tolerated and ignored) are
skipped, as are lines longer than 1024 bytes.
Decoding starts with the first line that is shorter than 1024 bytes (including
the newline) and consists of only (at least one) valid base64 characters plus
optional whitespace.
Decoding stops when base64 padding is encountered, a soft end-of-input
character (B<->, see L<EVP_DecodeUpdate(3)>) occurs as the first byte after a
complete group of 4 valid base64 characters is decoded, or when an error occurs
(e.g. due to input characters other than valid base64 or whitespace).

If decoding stops as a result of an error, the first L<BIO_read(3)> that
returns no decoded data will typically return a negative result, rather
than 0 (which indicates normal end of input).
However, a negative return value can also occur if the underlying BIO
supports retries, see L<BIO_should_read(3)> and L<BIO_set_mem_eof_return(3)>.

BIO_flush() on a base64 BIO that is being written through is
used to signal that no more data is to be encoded: this is used
to flush the final block through the BIO.

The flag B<BIO_FLAGS_BASE64_NO_NL> can be set with BIO_set_flags().
For writing, it causes all data to be written on one line without
newline at the end.
For reading, it removes all expectations on newlines in the input data.

=head1 NOTES

Because of the format of base64 encoding the end of the encoded
block cannot always be reliably determined.

=head1 RETURN VALUES

BIO_f_base64() returns the base64 BIO method.

=head1 EXAMPLES

Base64 encode the string "Hello World\n" and write the result
to standard output:

 BIO *bio, *b64;
 char message[] = "Hello World \n";

 b64 = BIO_new(BIO_f_base64());
 bio = BIO_new_fp(stdout, BIO_NOCLOSE);
 BIO_push(b64, bio);
 BIO_write(b64, message, strlen(message));
 BIO_flush(b64);

 BIO_free_all(b64);

Read base64 encoded data from standard input and write the decoded
data to standard output:

 BIO *bio, *b64, *bio_out;
 char inbuf[512];
 int inlen;

 b64 = BIO_new(BIO_f_base64());
 bio = BIO_new_fp(stdin, BIO_NOCLOSE);
 bio_out = BIO_new_fp(stdout, BIO_NOCLOSE);
 BIO_push(b64, bio);
 while ((inlen = BIO_read(b64, inbuf, 512)) > 0)
     BIO_write(bio_out, inbuf, inlen);

 BIO_flush(bio_out);
 BIO_free_all(b64);

=head1 BUGS

The hyphen character (B<->) is treated as an ad hoc soft end-of-input
character when it occurs at the start of a base64 group of 4 encoded
characters.

This heuristic works to detect the ends of base64 blocks in PEM or
multi-part MIME, provided there are no stray hyphens in the middle
input.
But it is just a heuristic, and sufficiently unusual input could produce
unexpected results.

There should perhaps be some way of specifying a test that the BIO can perform
to reliably determine EOF (for example a MIME boundary).

It may be possible for L<BIO_read(3)> to return zero, rather than -1, even if
an error has been detected, more tests are needed to cover all the potential
error paths.

=head1 SEE ALSO

L<BIO_read(3)>,
L<BIO_should_read(3)>,
L<BIO_set_mem_eof_return(3)>,
L<EVP_DecodeUpdate(3)>.

=head1 COPYRIGHT

Copyright 2000-2024 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

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