mirror of https://github.com/openssl/openssl.git
137 lines
4.3 KiB
Plaintext
137 lines
4.3 KiB
Plaintext
=pod
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=head1 NAME
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BIO_f_base64 - base64 BIO filter
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=head1 SYNOPSIS
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=for openssl multiple includes
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#include <openssl/bio.h>
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#include <openssl/evp.h>
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const BIO_METHOD *BIO_f_base64(void);
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=head1 DESCRIPTION
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BIO_f_base64() returns the base64 BIO method. This is a filter
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BIO that base64 encodes any data written through it and decodes
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any data read through it.
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Base64 BIOs do not support BIO_gets() or BIO_puts().
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For writing, by default output is divided to lines of length 64
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characters and there is a newline at the end of output.
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This behavior can be changed with B<BIO_FLAGS_BASE64_NO_NL> flag.
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For reading, the first line of base64 content should be at most 1024 bytes long
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including newline unless the flag B<BIO_FLAGS_BASE64_NO_NL> is set.
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Subsequent input lines can be of any length (i.e., newlines may appear anywhere
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in the input) and a newline at the end of input is not needed.
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Also when reading, unless the flag B<BIO_FLAGS_BASE64_NO_NL> is set, initial
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lines that contain non-base64 content (whitespace is tolerated and ignored) are
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skipped, as are lines longer than 1024 bytes.
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Decoding starts with the first line that is shorter than 1024 bytes (including
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the newline) and consists of only (at least one) valid base64 characters plus
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optional whitespace.
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Decoding stops when base64 padding is encountered, a soft end-of-input
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character (B<->, see L<EVP_DecodeUpdate(3)>) occurs as the first byte after a
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complete group of 4 valid base64 characters is decoded, or when an error occurs
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(e.g. due to input characters other than valid base64 or whitespace).
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If decoding stops as a result of an error, the first L<BIO_read(3)> that
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returns no decoded data will typically return a negative result, rather
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than 0 (which indicates normal end of input).
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However, a negative return value can also occur if the underlying BIO
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supports retries, see L<BIO_should_read(3)> and L<BIO_set_mem_eof_return(3)>.
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BIO_flush() on a base64 BIO that is being written through is
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used to signal that no more data is to be encoded: this is used
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to flush the final block through the BIO.
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The flag B<BIO_FLAGS_BASE64_NO_NL> can be set with BIO_set_flags().
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For writing, it causes all data to be written on one line without
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newline at the end.
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For reading, it removes all expectations on newlines in the input data.
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=head1 NOTES
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Because of the format of base64 encoding the end of the encoded
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block cannot always be reliably determined.
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=head1 RETURN VALUES
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BIO_f_base64() returns the base64 BIO method.
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=head1 EXAMPLES
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Base64 encode the string "Hello World\n" and write the result
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to standard output:
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BIO *bio, *b64;
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char message[] = "Hello World \n";
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b64 = BIO_new(BIO_f_base64());
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bio = BIO_new_fp(stdout, BIO_NOCLOSE);
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BIO_push(b64, bio);
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BIO_write(b64, message, strlen(message));
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BIO_flush(b64);
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BIO_free_all(b64);
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Read base64 encoded data from standard input and write the decoded
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data to standard output:
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BIO *bio, *b64, *bio_out;
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char inbuf[512];
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int inlen;
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b64 = BIO_new(BIO_f_base64());
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bio = BIO_new_fp(stdin, BIO_NOCLOSE);
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bio_out = BIO_new_fp(stdout, BIO_NOCLOSE);
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BIO_push(b64, bio);
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while ((inlen = BIO_read(b64, inbuf, 512)) > 0)
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BIO_write(bio_out, inbuf, inlen);
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BIO_flush(bio_out);
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BIO_free_all(b64);
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=head1 BUGS
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The hyphen character (B<->) is treated as an ad hoc soft end-of-input
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character when it occurs at the start of a base64 group of 4 encoded
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characters.
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This heuristic works to detect the ends of base64 blocks in PEM or
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multi-part MIME, provided there are no stray hyphens in the middle
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input.
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But it is just a heuristic, and sufficiently unusual input could produce
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unexpected results.
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There should perhaps be some way of specifying a test that the BIO can perform
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to reliably determine EOF (for example a MIME boundary).
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It may be possible for L<BIO_read(3)> to return zero, rather than -1, even if
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an error has been detected, more tests are needed to cover all the potential
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error paths.
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=head1 SEE ALSO
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L<BIO_read(3)>,
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L<BIO_should_read(3)>,
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L<BIO_set_mem_eof_return(3)>,
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L<EVP_DecodeUpdate(3)>.
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=head1 COPYRIGHT
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Copyright 2000-2024 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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