1=pod 2 3=head1 NAME 4 5BIO_read_ex, BIO_write_ex, BIO_read, BIO_write, BIO_gets, BIO_puts 6- BIO I/O functions 7 8=head1 SYNOPSIS 9 10 #include <openssl/bio.h> 11 12 int BIO_read_ex(BIO *b, void *data, size_t dlen, size_t *readbytes); 13 int BIO_write_ex(BIO *b, const void *data, size_t dlen, size_t *written); 14 15 int BIO_read(BIO *b, void *data, int dlen); 16 int BIO_gets(BIO *b, char *buf, int size); 17 int BIO_write(BIO *b, const void *data, int dlen); 18 int BIO_puts(BIO *b, const char *buf); 19 20=head1 DESCRIPTION 21 22BIO_read_ex() attempts to read B<dlen> bytes from BIO B<b> and places the data 23in B<data>. If any bytes were successfully read then the number of bytes read is 24stored in B<*readbytes>. 25 26BIO_write_ex() attempts to write B<dlen> bytes from B<data> to BIO B<b>. If 27successful then the number of bytes written is stored in B<*written>. 28 29BIO_read() attempts to read B<len> bytes from BIO B<b> and places 30the data in B<buf>. 31 32BIO_gets() performs the BIOs "gets" operation and places the data 33in B<buf>. Usually this operation will attempt to read a line of data 34from the BIO of maximum length B<size-1>. There are exceptions to this, 35however; for example, BIO_gets() on a digest BIO will calculate and 36return the digest and other BIOs may not support BIO_gets() at all. 37The returned string is always NUL-terminated and the '\n' is preserved 38if present in the input data. 39 40BIO_write() attempts to write B<len> bytes from B<buf> to BIO B<b>. 41 42BIO_puts() attempts to write a NUL-terminated string B<buf> to BIO B<b>. 43 44=head1 RETURN VALUES 45 46BIO_read_ex() and BIO_write_ex() return 1 if data was successfully read or 47written, and 0 otherwise. 48 49All other functions return either the amount of data successfully read or 50written (if the return value is positive) or that no data was successfully 51read or written if the result is 0 or -1. If the return value is -2 then 52the operation is not implemented in the specific BIO type. The trailing 53NUL is not included in the length returned by BIO_gets(). 54 55=head1 NOTES 56 57A 0 or -1 return is not necessarily an indication of an error. In 58particular when the source/sink is nonblocking or of a certain type 59it may merely be an indication that no data is currently available and that 60the application should retry the operation later. 61 62One technique sometimes used with blocking sockets is to use a system call 63(such as select(), poll() or equivalent) to determine when data is available 64and then call read() to read the data. The equivalent with BIOs (that is call 65select() on the underlying I/O structure and then call BIO_read() to 66read the data) should B<not> be used because a single call to BIO_read() 67can cause several reads (and writes in the case of SSL BIOs) on the underlying 68I/O structure and may block as a result. Instead select() (or equivalent) 69should be combined with non blocking I/O so successive reads will request 70a retry instead of blocking. 71 72See L<BIO_should_retry(3)> for details of how to 73determine the cause of a retry and other I/O issues. 74 75If the BIO_gets() function is not supported by a BIO then it possible to 76work around this by adding a buffering BIO L<BIO_f_buffer(3)> 77to the chain. 78 79=head1 SEE ALSO 80 81L<BIO_should_retry(3)> 82 83=head1 HISTORY 84 85BIO_gets() on 1.1.0 and older when called on BIO_fd() based BIO does not 86keep the '\n' at the end of the line in the buffer. 87 88=head1 COPYRIGHT 89 90Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved. 91 92Licensed under the OpenSSL license (the "License"). You may not use 93this file except in compliance with the License. You can obtain a copy 94in the file LICENSE in the source distribution or at 95L<https://www.openssl.org/source/license.html>. 96 97=cut 98