BIO I/O functions
void *buf, int len);
char *buf, int size);
const void *buf, int len);
const char *buf);
attempts to read len bytes from BIO
b and places the data in
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
- 1. There are exceptions to this however, for
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
attempts to write len bytes from
buf to BIO b.
attempts to write a null terminated string buf to BIO
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(2) to read the data. The equivalent with BIOs (that is
call select(2) on the underlying I/O structure and then call
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.
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.
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. The
trailing NUL is not included in the length returned by
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.