xref: /openbsd-src/lib/libssl/man/SSL_get_error.3 (revision af52a8c1be91646ffbd18ed2c70b9247ee5623a3)

.\"	$OpenBSD: SSL_get_error.3,v 1.5 2018/04/29 07:37:01 guenther Exp $
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.Dd $Mdocdate: April 29 2018 $
.Dt SSL_GET_ERROR 3
.Os
.Sh NAME
.Nm SSL_get_error
.Nd obtain result code for TLS/SSL I/O operation
.Sh SYNOPSIS
.In openssl/ssl.h
.Ft int
.Fn SSL_get_error "const SSL *ssl" "int ret"
.Sh DESCRIPTION
.Fn SSL_get_error
returns a result code (suitable for the C
.Dq switch
statement) for a preceding call to
.Xr SSL_connect 3 ,
.Xr SSL_accept 3 ,
.Xr SSL_do_handshake 3 ,
.Xr SSL_read 3 ,
.Xr SSL_peek 3 ,
or
.Xr SSL_write 3
on
.Fa ssl .
The value returned by that TLS/SSL I/O function must be passed to
.Fn SSL_get_error
in parameter
.Fa ret .
.Pp
In addition to
.Fa ssl
and
.Fa ret ,
.Fn SSL_get_error
inspects the current thread's OpenSSL error queue.
Thus,
.Fn SSL_get_error
must be used in the same thread that performed the TLS/SSL I/O operation,
and no other OpenSSL function calls should appear in between.
The current thread's error queue must be empty before the TLS/SSL I/O operation
is attempted, or
.Fn SSL_get_error
will not work reliably.
.Sh RETURN VALUES
The following return values can currently occur:
.Bl -tag -width Ds
.It Dv SSL_ERROR_NONE
The TLS/SSL I/O operation completed.
This result code is returned if and only if
.Fa ret
> 0.
.It Dv SSL_ERROR_ZERO_RETURN
The TLS/SSL connection has been closed.
If the protocol version is SSL 3.0 or TLS 1.0, this result code is returned
only if a closure alert has occurred in the protocol, i.e., if the connection
has been closed cleanly.
Note that in this case
.Dv SSL_ERROR_ZERO_RETURN
does not necessarily indicate that the underlying transport has been closed.
.It Dv SSL_ERROR_WANT_READ , Dv SSL_ERROR_WANT_WRITE
The operation did not complete;
the same TLS/SSL I/O function should be called again later.
If, by then, the underlying
.Vt BIO
has data available for reading (if the result code is
.Dv SSL_ERROR_WANT_READ )
or allows writing data
.Pq Dv SSL_ERROR_WANT_WRITE ,
then some TLS/SSL protocol progress will take place,
i.e., at least part of a TLS/SSL record will be read or written.
Note that the retry may again lead to a
.Dv SSL_ERROR_WANT_READ
or
.Dv SSL_ERROR_WANT_WRITE
condition.
There is no fixed upper limit for the number of iterations that may be
necessary until progress becomes visible at application protocol level.
.Pp
For socket
.Fa BIO Ns
s (e.g., when
.Fn SSL_set_fd
was used),
.Xr select 2
or
.Xr poll 2
on the underlying socket can be used to find out when the TLS/SSL I/O function
should be retried.
.Pp
Caveat: Any TLS/SSL I/O function can lead to either of
.Dv SSL_ERROR_WANT_READ
and
.Dv SSL_ERROR_WANT_WRITE .
In particular,
.Xr SSL_read 3
or
.Xr SSL_peek 3
may want to write data and
.Xr SSL_write 3
may want
to read data.
This is mainly because TLS/SSL handshakes may occur at any time during the
protocol (initiated by either the client or the server);
.Xr SSL_read 3 ,
.Xr SSL_peek 3 ,
and
.Xr SSL_write 3
will handle any pending handshakes.
.It Dv SSL_ERROR_WANT_CONNECT , Dv SSL_ERROR_WANT_ACCEPT
The operation did not complete; the same TLS/SSL I/O function should be
called again later.
The underlying BIO was not connected yet to the peer and the call would block
in
.Xr connect 2 Ns / Ns
.Xr accept 2 .
The SSL function should be
called again when the connection is established.
These messages can only appear with a
.Xr BIO_s_connect 3
or
.Xr BIO_s_accept 3
.Vt BIO ,
respectively.
In order to find out when the connection has been successfully established,
on many platforms
.Xr select 2
or
.Xr poll 2
for writing on the socket file descriptor can be used.
.It Dv SSL_ERROR_WANT_X509_LOOKUP
The operation did not complete because an application callback set by
.Xr SSL_CTX_set_client_cert_cb 3
has asked to be called again.
The TLS/SSL I/O function should be called again later.
Details depend on the application.
.It Dv SSL_ERROR_SYSCALL
Some I/O error occurred.
The OpenSSL error queue may contain more information on the error.
If the error queue is empty (i.e.,
.Fn ERR_get_error
returns 0),
.Fa ret
can be used to find out more about the error:
If
.Fa ret
== 0, an
.Dv EOF
was observed that violates the protocol.
If
.Fa ret
== \(mi1, the underlying
.Vt BIO
reported an
I/O error (for socket I/O on Unix systems, consult
.Dv errno
for details).
.It Dv SSL_ERROR_SSL
A failure in the SSL library occurred, usually a protocol error.
The OpenSSL error queue contains more information on the error.
.El
.Sh SEE ALSO
.Xr err 3 ,
.Xr ssl 3
.Sh HISTORY
.Fn SSL_get_error
first appeared in SSLeay 0.8.0 and have been available since
.Ox 2.4 .