NAME
BIO_read,
BIO_write, BIO_gets,
BIO_puts —
BIO I/O functions
SYNOPSIS
#include
<openssl/bio.h>
int
BIO_read(BIO *b,
void *buf, int len);
int
BIO_gets(BIO *b,
char *buf, int size);
int
BIO_write(BIO *b,
const void *buf, int len);
int
BIO_puts(BIO *b,
const char *buf);
DESCRIPTION
BIO_read()
attempts to read len bytes from BIO
b and places the data in
buf.
BIO_gets()
performs the BIOs "gets" operation and places the data in
buf. Usually this operation will attempt to read a
line of data from the BIO of maximum length len. 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.
BIO_write()
attempts to write len bytes from
buf to BIO b.
BIO_puts()
attempts to write a null terminated string buf to BIO
b.
RETURN VALUES
All these 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.
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(2), poll(2) or equivalent) to determine when data is available
and then call read(3) to read the data. The equivalent with BIOs (that is
call select(2) on the underlying I/O structure and then call
BIO_read()
to read the data) should
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(2) (or equivalent) should be combined with non blocking I/O so
successive reads will request a retry instead of blocking.
See 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 is possible to work around this
by adding a buffering BIO
BIO_f_buffer(3) to the chain.