NAME
BIO_read,
BIO_number_read, BIO_gets,
BIO_write, BIO_puts,
BIO_indent,
BIO_number_written —
BIO I/O functions
SYNOPSIS
#include
<openssl/bio.h>
int
BIO_read(BIO *b,
void *buf, int len);
unsigned long
BIO_number_read(BIO *b);
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 *string);
int
BIO_indent(BIO *b,
int indent, int max);
unsigned long
BIO_number_written(BIO *b);
DESCRIPTION
BIO_read()
attempts to read len bytes from
b and places the data in
buf.
BIO_number_read()
returns the grand total of bytes read from b using
BIO_read() so far. Bytes read with
BIO_gets() do not count.
BIO_new(3) and BIO_set(3) initialize the counter to 0. When reading very
large amounts of data, the counter will eventually wrap around from
ULONG_MAX to 0.
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 size
- 1. 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. The returned string is always
NUL-terminated.
BIO_write()
attempts to write len bytes from
buf to b.
BIO_puts()
attempts to write the NUL-terminated string to
b.
BIO_indent()
attempts to write indent space characters to
b, but not more than max
characters.
BIO_number_written()
returns the grand total of bytes written to b using
BIO_write(), BIO_puts(), and
BIO_indent() so far.
BIO_new(3) and BIO_set(3) initialize the counter to 0. When writing very
large amounts of data, the counter will eventually wrap around from
ULONG_MAX to 0.
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
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(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.
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(3) to the chain.
RETURN VALUES
BIO_indent() returns 1 if successful, even
if nothing was written, or 0 if writing fails.
BIO_number_read() and
BIO_number_written() return a number of bytes or 0
if b is a NULL pointer.
The other 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
BIO_gets().
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.
SEE ALSO
HISTORY
BIO_read(),
BIO_gets(), BIO_write(), and
BIO_puts() first appeared in SSLeay 0.6.0.
BIO_number_read() and
BIO_number_written() first appeared in SSLeay 0.6.5.
These functions have been available since OpenBSD
2.4.
BIO_indent() first appeared in OpenSSL
0.9.7 and has been available since OpenBSD 3.4.