BIO_read
Section: OpenSSL (3)
Updated: 2017-05-25
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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
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUES
-
- NOTES
-
- SEE ALSO
-
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