BIO_F_BASE64(3ossl) OpenSSL BIO_F_BASE64(3ossl)
NAME
BIO_f_base64 - base64 BIO filter
SYNOPSIS
#include <openssl/bio.h>
#include <openssl/evp.h>
const BIO_METHOD *BIO_f_base64(void);
DESCRIPTION
BIO_f_base64(3) 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 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 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 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 (-, see
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 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
BIO_should_read(3) and 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 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.
NOTES
Because of the format of base64 encoding the end of the encoded block
cannot always be reliably determined.
RETURN VALUES
BIO_f_base64(3) returns the base64 BIO method.
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);
BUGS
The hyphen character (-) 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 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.
SEE ALSO
BIO_read(3), BIO_should_read(3), BIO_set_mem_eof_return(3),
EVP_DecodeUpdate(3).
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
<https://www.openssl.org/source/license.html>.
3.4.0 2024-10-29 BIO_F_BASE64(3ossl)
openssl 3.4.0 - Generated Fri Nov 1 15:27:28 CDT 2024