=pod

=head1 NAME

BIO_read_ex, BIO_write_ex, BIO_read, BIO_write, BIO_gets, BIO_puts

- BIO I/O functions

=head1 SYNOPSIS

 #include <openssl/bio.h>

 int BIO_read_ex(BIO *b, void *data, size_t dlen, size_t *readbytes);

 int BIO_write_ex(BIO *b, const void *data, size_t dlen, size_t *written);

 int BIO_read(BIO *b, void *data, int dlen);

 int BIO_gets(BIO *b, char *buf, int size);

 int BIO_write(BIO *b, const void *data, int dlen);

 int BIO_puts(BIO *b, const char *buf);

=head1 DESCRIPTION

BIO_read_ex() attempts to read B<dlen> bytes from BIO B and places the data

in B<data>. If any bytes were successfully read then the number of bytes read is

stored in B<*readbytes>.

BIO_write_ex() attempts to write B<dlen> bytes from B<data> to BIO B. If

successful then the number of bytes written is stored in B<*written>.

BIO_read() attempts to read B<len> bytes from BIO B and places

the data in B<buf>.

BIO_gets() performs the BIOs "gets" operation and places the data

in B<buf>. Usually this operation will attempt to read a line of data

from the BIO of maximum length B<size-1>. There are exceptions to this,

however; for example, BIO_gets() on a digest BIO will calculate and

return the digest and other BIOs may not support BIO_gets() at all.

The returned string is always NUL-terminated and the '\n' is preserved

if present in the input data.

BIO_write() attempts to write B<len> bytes from B<buf> to BIO B.

BIO_puts() attempts to write a NUL-terminated string B<buf> to BIO B.

=head1 RETURN VALUES

BIO_read_ex() and BIO_write_ex() return 1 if data was successfully read or

written, and 0 otherwise.

All other functions return either the amount of data successfully read or

written (if the return value is positive) or that no data was successfully

read or written if the result is 0 or -1. If the return value is -2 then

the operation is not implemented in the specific BIO type.  The trailing

NUL is not included in the length returned by BIO_gets().

=head1 NOTES

A 0 or -1 return is not necessarily an indication of an error. In

particular when the source/sink is non-blocking or of a certain type

it may merely be an indication that no data is currently available and that

the application should retry the operation later.

One technique sometimes used with blocking sockets is to use a system call

(such as select(), poll() or equivalent) to determine when data is available

and then call read() to read the data. The equivalent with BIOs (that is call

select() on the underlying I/O structure and then call BIO_read() to

read the data) should B<not> be used because a single call to BIO_read()

can cause several reads (and writes in the case of SSL BIOs) on the underlying

I/O structure and may block as a result. Instead select() (or equivalent)

should be combined with non blocking I/O so successive reads will request

a retry instead of blocking.

See L<BIO_should_retry(3)> for details of how to

determine the cause of a retry and other I/O issues.

If the BIO_gets() function is not supported by a BIO then it possible to

work around this by adding a buffering BIO L<BIO_f_buffer(3)>

to the chain.

=head1 SEE ALSO

L<BIO_should_retry(3)>

=head1 HISTORY

BIO_gets() on 1.1.0 and older when called on BIO_fd() based BIO does not

keep the '\n' at the end of the line in the buffer.

=head1 COPYRIGHT

Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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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