BIO_read, BIO_write, BIO_gets, BIO_puts - BIO I/O functions
int len ); int BIO_gets(
int size ); int BIO_write(
const void *buf,
int len ); int BIO_puts(
const char *buf );
The BIO_read() function attempts to read len bytes from
BIO b and places the data in buf.
The BIO_gets() function 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. However, there are exceptions to this. For
example, BIO_gets() on a digest BIO will calculate and
return the digest, and other BIOs might not support
The BIO_write() function attempts to write len bytes from
buf to BIO b.
The BIO_puts() function attempts to write a null terminated
string buf to BIO b
A 0 or -1 return might indicate an error. However, when
the source/sink is non-blocking or of a certain type, it
might be an indication that no data is 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 nonblocking
I/O so successive reads will request a retry instead
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(), 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.
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