mirror of https://github.com/openssl/openssl
130 lines
5.1 KiB
Plaintext
130 lines
5.1 KiB
Plaintext
=pod
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=head1 NAME
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BIO_read_ex, BIO_write_ex, BIO_read, BIO_write,
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BIO_gets, BIO_get_line, BIO_puts
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- BIO I/O functions
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=head1 SYNOPSIS
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#include <openssl/bio.h>
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int BIO_read_ex(BIO *b, void *data, size_t dlen, size_t *readbytes);
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int BIO_write_ex(BIO *b, const void *data, size_t dlen, size_t *written);
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int BIO_read(BIO *b, void *data, int dlen);
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int BIO_gets(BIO *b, char *buf, int size);
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int BIO_get_line(BIO *b, char *buf, int size);
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int BIO_write(BIO *b, const void *data, int dlen);
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int BIO_puts(BIO *b, const char *buf);
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=head1 DESCRIPTION
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BIO_read_ex() attempts to read I<dlen> bytes from BIO I<b> and places the data
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in I<data>. If any bytes were successfully read then the number of bytes read is
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stored in I<*readbytes>.
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BIO_write_ex() attempts to write I<dlen> bytes from I<data> to BIO I<b>.
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If successful then the number of bytes written is stored in I<*written>
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unless I<written> is NULL.
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BIO_read() attempts to read I<len> bytes from BIO I<b> and places
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the data in I<buf>.
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BIO_gets() performs the BIOs "gets" operation and places the data
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in I<buf>. Usually this operation will attempt to read a line of data
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from the BIO of maximum length I<size-1>. There are exceptions to this,
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however; for example, BIO_gets() on a digest BIO will calculate and
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return the digest and other BIOs may not support BIO_gets() at all.
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The returned string is always NUL-terminated and the '\n' is preserved
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if present in the input data.
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On binary input there may be NUL characters within the string;
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in this case the return value (if nonnegative) may give an incorrect length.
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BIO_get_line() attempts to read from BIO I<b> a line of data up to the next '\n'
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or the maximum length I<size-1> is reached and places the data in I<buf>.
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The returned string is always NUL-terminated and the '\n' is preserved
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if present in the input data.
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On binary input there may be NUL characters within the string;
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in this case the return value (if nonnegative) gives the actual length read.
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For implementing this, unfortunately the data needs to be read byte-by-byte.
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BIO_write() attempts to write I<len> bytes from I<buf> to BIO I<b>.
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BIO_puts() attempts to write a NUL-terminated string I<buf> to BIO I<b>.
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=head1 RETURN VALUES
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BIO_read_ex() returns 1 if data was successfully read, and 0 otherwise.
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BIO_write_ex() returns 1 if no error was encountered writing data, 0 otherwise.
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Requesting to write 0 bytes is not considered an error.
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BIO_write() returns -2 if the "write" operation is not implemented by the BIO
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or -1 on other errors.
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Otherwise it returns the number of bytes written.
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This may be 0 if the BIO I<b> is NULL or I<dlen <= 0>.
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BIO_gets() returns -2 if the "gets" operation is not implemented by the BIO
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or -1 on other errors.
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Otherwise it typically returns the amount of data read,
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but depending on the implementation it may return only the length up to
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the first NUL character contained in the data read.
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In any case the trailing NUL that is added after the data read
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is not included in the length returned.
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All other functions return either the amount of data successfully read or
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written (if the return value is positive) or that no data was successfully
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read or written if the result is 0 or -1. If the return value is -2 then
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the operation is not implemented in the specific BIO type.
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=head1 NOTES
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A 0 or -1 return is not necessarily an indication of an error. In
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particular when the source/sink is nonblocking or of a certain type
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it may merely be an indication that no data is currently available and that
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the application should retry the operation later.
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One technique sometimes used with blocking sockets is to use a system call
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(such as select(), poll() or equivalent) to determine when data is available
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and then call read() to read the data. The equivalent with BIOs (that is call
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select() on the underlying I/O structure and then call BIO_read() to
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read the data) should B<not> be used because a single call to BIO_read()
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can cause several reads (and writes in the case of SSL BIOs) on the underlying
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I/O structure and may block as a result. Instead select() (or equivalent)
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should be combined with non blocking I/O so successive reads will request
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a retry instead of blocking.
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See L<BIO_should_retry(3)> for details of how to
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determine the cause of a retry and other I/O issues.
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If the "gets" method is not supported by a BIO then BIO_get_line() can be used.
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It is also possible to make BIO_gets() usable even if the "gets" method is not
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supported by adding a buffering BIO L<BIO_f_buffer(3)> to the chain.
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=head1 SEE ALSO
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L<BIO_should_retry(3)>
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=head1 HISTORY
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BIO_gets() on 1.1.0 and older when called on BIO_fd() based BIO did not
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keep the '\n' at the end of the line in the buffer.
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BIO_get_line() was added in OpenSSL 3.0.
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BIO_write_ex() returns 1 if the size of the data to write is 0 and the
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I<written> parameter of the function can be NULL since OpenSSL 3.0.
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=head1 COPYRIGHT
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Copyright 2000-2023 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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