BIO_read, BIO_write, BIO_gets, BIO_puts - BIO I/O functions
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);
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
on a digest BIO will calculate and return the digest and other BIOs may not
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
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.
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
poll() or equivalent) to
determine when data is available and then call
read() to read
the data. The equivalent with BIOs (that is call
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.
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.