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.\" ========================================================================
.\"
.IX Title "SSL_CTX_set_mode 3"
.TH SSL_CTX_set_mode 3 "2019-12-20" "1.0.2u" "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_set_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_set_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"
\&\fBSSL_CTX_set_mode()\fR adds the mode set via bitmask in \fBmode\fR to \fBctx\fR.
Options already set before are not cleared.
.PP
\&\fBSSL_set_mode()\fR adds the mode set via bitmask in \fBmode\fR to \fBssl\fR.
Options already set before are not cleared.
.PP
\&\fBSSL_CTX_get_mode()\fR returns the mode set for \fBctx\fR.
.PP
\&\fBSSL_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(..., n) to return r with 0 < r < n (i.e. report success
when just a single record has been written). When not set (the default),
\&\fBSSL_write()\fR will only report success once the complete chunk was written.
Once \fBSSL_write()\fR returns with r, r bytes have been successfully written
and the next call to \fBSSL_write()\fR must only send the n\-r bytes left,
imitating the behaviour of \fBwrite()\fR.
.IP "\s-1SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER\s0" 4
.IX Item "SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER"
Make it possible to retry \fBSSL_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 \fBSSL_write()\fR behaves like
non-blocking \fBwrite()\fR.
.IP "\s-1SSL_MODE_AUTO_RETRY\s0" 4
.IX Item "SSL_MODE_AUTO_RETRY"
Never bother the application with retries if the transport is blocking.
If a renegotiation take place during normal operation, a
\&\fBSSL_read\fR\|(3) or \fBSSL_write\fR\|(3) would return
with \-1 and indicate the need to retry with \s-1SSL_ERROR_WANT_READ.\s0
In a non-blocking environment applications must be prepared to handle
incomplete read/write operations.
In a blocking environment, applications are not always prepared to
deal with read/write operations returning without success report. The
flag \s-1SSL_MODE_AUTO_RETRY\s0 will cause read/write operations to only
return after the handshake and successful completion.
.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.  Released memory is
either appended to a list of unused \s-1RAM\s0 chunks on the \s-1SSL_CTX,\s0 or simply
freed if the list of unused chunks would become longer than 
\&\s-1SSL_CTX\-\s0>freelist_max_len, which defaults to 32.  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.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBSSL_CTX_set_mode()\fR and \fBSSL_set_mode()\fR return the new mode bitmask
after adding \fBmode\fR.
.PP
\&\fBSSL_CTX_get_mode()\fR and \fBSSL_get_mode()\fR return the current bitmask.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBssl\fR\|(3), \fBSSL_read\fR\|(3), \fBSSL_write\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\s-1SSL_MODE_AUTO_RETRY\s0 as been added in OpenSSL 0.9.6.