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.\" ========================================================================
.\"
.IX Title "SSL_CTX_SET_MODE 3"
.TH SSL_CTX_SET_MODE 3 "2018-11-20" "1.1.1a" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
SSL_CTX_set_mode, SSL_CTX_clear_mode, SSL_set_mode, SSL_clear_mode, SSL_CTX_get_mode, SSL_get_mode \- manipulate SSL engine mode
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/ssl.h>
\&
\& long SSL_CTX_set_mode(SSL_CTX *ctx, long mode);
\& long SSL_CTX_clear_mode(SSL_CTX *ctx, long mode);
\& long SSL_set_mode(SSL *ssl, long mode);
\& long SSL_clear_mode(SSL *ssl, long mode);
\&
\& long SSL_CTX_get_mode(SSL_CTX *ctx);
\& long SSL_get_mode(SSL *ssl);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fISSL_CTX_set_mode()\fR adds the mode set via bitmask in \fBmode\fR to \fBctx\fR.
Options already set before are not cleared.
\&\fISSL_CTX_clear_mode()\fR removes the mode set via bitmask in \fBmode\fR from \fBctx\fR.
.PP
\&\fISSL_set_mode()\fR adds the mode set via bitmask in \fBmode\fR to \fBssl\fR.
Options already set before are not cleared.
\&\fISSL_clear_mode()\fR removes the mode set via bitmask in \fBmode\fR from \fBssl\fR.
.PP
\&\fISSL_CTX_get_mode()\fR returns the mode set for \fBctx\fR.
.PP
\&\fISSL_get_mode()\fR returns the mode set for \fBssl\fR.
.SH "NOTES"
.IX Header "NOTES"
The following mode changes are available:
.IP "\s-1SSL_MODE_ENABLE_PARTIAL_WRITE\s0" 4
.IX Item "SSL_MODE_ENABLE_PARTIAL_WRITE"
Allow SSL_write_ex(..., n, &r) to return with 0 < r < n (i.e. report success
when just a single record has been written). This works in a similar way for
\&\fISSL_write()\fR. When not set (the default), \fISSL_write_ex()\fR or \fISSL_write()\fR will only
report success once the complete chunk was written. Once \fISSL_write_ex()\fR or
\&\fISSL_write()\fR returns successful, \fBr\fR bytes have been written and the next call
to \fISSL_write_ex()\fR or \fISSL_write()\fR must only send the n\-r bytes left, imitating
the behaviour of \fIwrite()\fR.
.IP "\s-1SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER\s0" 4
.IX Item "SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER"
Make it possible to retry \fISSL_write_ex()\fR or \fISSL_write()\fR with changed buffer
location (the buffer contents must stay the same). This is not the default to
avoid the misconception that non-blocking \fISSL_write()\fR behaves like
non-blocking \fIwrite()\fR.
.IP "\s-1SSL_MODE_AUTO_RETRY\s0" 4
.IX Item "SSL_MODE_AUTO_RETRY"
During normal operations, non-application data records might need to be sent or
received that the application is not aware of.
If a non-application data record was processed,
\&\fISSL_read_ex\fR\|(3) and \fISSL_read\fR\|(3) can return with a failure and indicate the
need to retry with \fB\s-1SSL_ERROR_WANT_READ\s0\fR.
If such a non-application data record was processed, the flag
\&\fB\s-1SSL_MODE_AUTO_RETRY\s0\fR causes it to try to process the next record instead of
returning.
.Sp
In a non-blocking environment applications must be prepared to handle
incomplete read/write operations.
Setting \fB\s-1SSL_MODE_AUTO_RETRY\s0\fR for a non-blocking \fB\s-1BIO\s0\fR will process
non-application data records until either no more data is available or
an application data record has been processed.
.Sp
In a blocking environment, applications are not always prepared to
deal with the functions returning intermediate reports such as retry
requests, and setting the \fB\s-1SSL_MODE_AUTO_RETRY\s0\fR flag will cause the functions
to only return after successfully processing an application data record or a
failure.
.Sp
Turning off \fB\s-1SSL_MODE_AUTO_RETRY\s0\fR can be useful with blocking \fB\s-1BIO\s0\fRs in case
they are used in combination with something like \fIselect()\fR or \fIpoll()\fR.
Otherwise the call to \fISSL_read()\fR or \fISSL_read_ex()\fR might hang when a
non-application record was sent and no application data was sent.
.IP "\s-1SSL_MODE_RELEASE_BUFFERS\s0" 4
.IX Item "SSL_MODE_RELEASE_BUFFERS"
When we no longer need a read buffer or a write buffer for a given \s-1SSL,\s0
then release the memory we were using to hold it.
Using this flag can
save around 34k per idle \s-1SSL\s0 connection.
This flag has no effect on \s-1SSL\s0 v2 connections, or on \s-1DTLS\s0 connections.
.IP "\s-1SSL_MODE_SEND_FALLBACK_SCSV\s0" 4
.IX Item "SSL_MODE_SEND_FALLBACK_SCSV"
Send \s-1TLS_FALLBACK_SCSV\s0 in the ClientHello.
To be set only by applications that reconnect with a downgraded protocol
version; see draft\-ietf\-tls\-downgrade\-scsv\-00 for details.
.Sp
\&\s-1DO NOT ENABLE THIS\s0 if your application attempts a normal handshake.
Only use this in explicit fallback retries, following the guidance
in draft\-ietf\-tls\-downgrade\-scsv\-00.
.IP "\s-1SSL_MODE_ASYNC\s0" 4
.IX Item "SSL_MODE_ASYNC"
Enable asynchronous processing. \s-1TLS I/O\s0 operations may indicate a retry with
\&\s-1SSL_ERROR_WANT_ASYNC\s0 with this mode set if an asynchronous capable engine is
used to perform cryptographic operations. See \fISSL_get_error\fR\|(3).
.PP
All modes are off by default except for \s-1SSL_MODE_AUTO_RETRY\s0 which is on by
default since 1.1.1.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fISSL_CTX_set_mode()\fR and \fISSL_set_mode()\fR return the new mode bitmask
after adding \fBmode\fR.
.PP
\&\fISSL_CTX_get_mode()\fR and \fISSL_get_mode()\fR return the current bitmask.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIssl\fR\|(7), \fISSL_read_ex\fR\|(3), \fISSL_read\fR\|(3), \fISSL_write_ex\fR\|(3) or
\&\fISSL_write\fR\|(3), \fISSL_get_error\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\s-1SSL_MODE_ASYNC\s0 was first added to OpenSSL 1.1.0.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2001\-2018 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the OpenSSL license (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.