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(),
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
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
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
BIO_f_buffer(3) to the
chain.
SEE ALSO¶
BIO_should_retry(3)
TBA