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BIO_READ(3) | Library Functions Manual | BIO_READ(3) |
NAME
BIO_read
,
BIO_gets
,
BIO_write
,
BIO_puts
,
BIO_indent
—
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 *string);
int
BIO_indent
(BIO
*b, int indent,
int max);
DESCRIPTION
BIO_read
() attempts to read
len bytes from
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 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.
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.
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
BIO_meth_new(3), BIO_new(3), BIO_should_retry(3)HISTORY
BIO_read
(),
BIO_gets
(),
BIO_write
(), and
BIO_puts
() first appeared in SSLeay 0.6.0
and have been available since OpenBSD 2.4.
BIO_indent
() first appeared in OpenSSL 0.9.7
and has been available since OpenBSD 3.4.December 8, 2021 | Debian |