SSL_WRITE(3) | Library Functions Manual | SSL_WRITE(3) |
SSL_write
—
#include <openssl/ssl.h>
int
SSL_write
(SSL
*ssl, const void
*buf, int num);
SSL_write
() writes num bytes from
the buffer buf into the specified
ssl connection.
If necessary, SSL_write
() will negotiate a
TLS/SSL session, if not already explicitly performed by
SSL_connect(3) or
SSL_accept(3). If the peer requests a
re-negotiation, it will be performed transparently during the
SSL_write
() operation. The behaviour of
SSL_write
() depends on the underlying
BIO.
For the transparent negotiation to succeed, the
ssl must have been initialized to client or server
mode. This is being done by calling
SSL_set_connect_state(3)
or SSL_set_accept_state(3)
before the first call to an SSL_read(3)
or SSL_write
() function.
If the underlying BIO is
blocking, SSL_write
() will only
return once the write operation has been finished or an error occurred,
except when a renegotiation take place, in which case a
SSL_ERROR_WANT_READ
may occur. This behaviour can be
controlled with the SSL_MODE_AUTO_RETRY
flag of the
SSL_CTX_set_mode(3) call.
If the underlying BIO is
non-blocking, SSL_write
() will
also return when the underlying BIO could not satisfy
the needs of SSL_write
() to continue the operation.
In this case a call to
SSL_get_error(3) with the return
value of SSL_write
() will yield
SSL_ERROR_WANT_READ
or
SSL_ERROR_WANT_WRITE
. As at any time a
re-negotiation is possible, a call to SSL_write
()
can also cause read operations! The calling process then must repeat the
call after taking appropriate action to satisfy the needs of
SSL_write
(). The action depends on the underlying
BIO. When using a non-blocking socket, nothing is to
be done, but select(2) can be used to
check for the required condition. When using a buffering
BIO, like a BIO pair, data must
be written into or retrieved out of the BIO before being able to
continue.
SSL_write
() will only return with success
when the complete contents of buf of length
num have been written. This default behaviour can be
changed with the SSL_MODE_ENABLE_PARTIAL_WRITE
option of SSL_CTX_set_mode(3).
When this flag is set, SSL_write
() will also return
with success when a partial write has been successfully completed. In this
case the SSL_write
() operation is considered
completed. The bytes are sent and a new SSL_write
()
operation with a new buffer (with the already sent bytes removed) must be
started. A partial write is performed with the size of a message block,
which is 16kB.
When an SSL_write
() operation has to be
repeated because SSL_get_error(3)
returned SSL_ERROR_WANT_READ
or
SSL_ERROR_WANT_WRITE
, it must be repeated with the
same arguments.
When calling SSL_write
() with
num=0 bytes to be sent, the behaviour is
undefined.
SSL_ERROR_ZERO_RETURN
).SSL_write
() appeared in SSLeay 0.4 or earlier and has
been available since OpenBSD 2.4.March 27, 2018 | OpenBSD-current |