212 lines
7.5 KiB
Groff
Executable File
212 lines
7.5 KiB
Groff
Executable File
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.\" ========================================================================
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.\"
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.IX Title "SSL_CONNECT 3"
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.TH SSL_CONNECT 3 "2020-03-02" "3.0.0-dev" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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SSL_connect \- initiate the TLS/SSL handshake with an TLS/SSL server
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/ssl.h>
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\&
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\& int SSL_connect(SSL *ssl);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fISSL_connect()\fR initiates the \s-1TLS/SSL\s0 handshake with a server. The communication
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channel must already have been set and assigned to the \fBssl\fR by setting an
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underlying \fB\s-1BIO\s0\fR.
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.SH "NOTES"
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.IX Header "NOTES"
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The behaviour of \fISSL_connect()\fR depends on the underlying \s-1BIO\s0.
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.PP
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If the underlying \s-1BIO\s0 is \fBblocking\fR, \fISSL_connect()\fR will only return once the
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handshake has been finished or an error occurred.
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.PP
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If the underlying \s-1BIO\s0 is \fBnon-blocking\fR, \fISSL_connect()\fR will also return
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when the underlying \s-1BIO\s0 could not satisfy the needs of \fISSL_connect()\fR
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to continue the handshake, indicating the problem by the return value \-1.
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In this case a call to \fISSL_get_error()\fR with the
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return value of \fISSL_connect()\fR will yield \fB\s-1SSL_ERROR_WANT_READ\s0\fR or
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\&\fB\s-1SSL_ERROR_WANT_WRITE\s0\fR. The calling process then must repeat the call after
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taking appropriate action to satisfy the needs of \fISSL_connect()\fR.
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The action depends on the underlying \s-1BIO\s0. When using a non-blocking socket,
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nothing is to be done, but \fIselect()\fR can be used to check for the required
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condition. When using a buffering \s-1BIO\s0, like a \s-1BIO\s0 pair, data must be written
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into or retrieved out of the \s-1BIO\s0 before being able to continue.
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.PP
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Many systems implement Nagle's algorithm by default which means that it will
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buffer outgoing \s-1TCP\s0 data if a \s-1TCP\s0 packet has already been sent for which no
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corresponding \s-1ACK\s0 has been received yet from the peer. This can have performance
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impacts after a successful TLSv1.3 handshake or a successful TLSv1.2 (or below)
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resumption handshake, because the last peer to communicate in the handshake is
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the client. If the client is also the first to send application data (as is
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typical for many protocols) then this data could be buffered until an \s-1ACK\s0 has
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been received for the final handshake message.
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.PP
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The \fB\s-1TCP_NODELAY\s0\fR socket option is often available to disable Nagle's
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algorithm. If an application opts to disable Nagle's algorithm consideration
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should be given to turning it back on again later if appropriate. The helper
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function \fIBIO_set_tcp_ndelay()\fR can be used to turn on or off the \fB\s-1TCP_NODELAY\s0\fR
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option.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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The following return values can occur:
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.IP "0" 4
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The \s-1TLS/SSL\s0 handshake was not successful but was shut down controlled and
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by the specifications of the \s-1TLS/SSL\s0 protocol. Call \fISSL_get_error()\fR with the
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return value \fBret\fR to find out the reason.
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.IP "1" 4
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.IX Item "1"
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The \s-1TLS/SSL\s0 handshake was successfully completed, a \s-1TLS/SSL\s0 connection has been
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established.
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.IP "<0" 4
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.IX Item "<0"
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The \s-1TLS/SSL\s0 handshake was not successful, because a fatal error occurred either
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at the protocol level or a connection failure occurred. The shutdown was
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not clean. It can also occur of action is need to continue the operation
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for non-blocking BIOs. Call \fISSL_get_error()\fR with the return value \fBret\fR
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to find out the reason.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fISSL_get_error\fR\|(3), \fISSL_accept\fR\|(3),
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\&\fISSL_shutdown\fR\|(3), \fIssl\fR\|(7), \fIbio\fR\|(7),
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\&\fISSL_set_connect_state\fR\|(3),
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\&\fISSL_do_handshake\fR\|(3),
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\&\fISSL_CTX_new\fR\|(3)
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2000\-2018 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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