224 lines
8.1 KiB
Groff
224 lines
8.1 KiB
Groff
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.\" ========================================================================
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.\"
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.IX Title "SSL_write 3"
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.TH SSL_write 3 "2014-08-06" "1.0.1i" "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_write \- write bytes to a TLS/SSL connection.
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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_write(SSL *ssl, const void *buf, int num);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fISSL_write()\fR writes \fBnum\fR bytes from the buffer \fBbuf\fR into the specified
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\&\fBssl\fR connection.
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.SH "NOTES"
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.IX Header "NOTES"
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If necessary, \fISSL_write()\fR will negotiate a \s-1TLS/SSL\s0 session, if
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not already explicitly performed by \fISSL_connect\fR\|(3) or
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\&\fISSL_accept\fR\|(3). If the
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peer requests a re-negotiation, it will be performed transparently during
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the \fISSL_write()\fR operation. The behaviour of \fISSL_write()\fR depends on the
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underlying \s-1BIO\s0.
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.PP
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For the transparent negotiation to succeed, the \fBssl\fR must have been
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initialized to client or server mode. This is being done by calling
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\&\fISSL_set_connect_state\fR\|(3) or \fISSL_set_accept_state()\fR
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before the first call to an \fISSL_read\fR\|(3) or \fISSL_write()\fR function.
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.PP
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If the underlying \s-1BIO\s0 is \fBblocking\fR, \fISSL_write()\fR will only return, once the
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write operation has been finished or an error occurred, except when a
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renegotiation take place, in which case a \s-1SSL_ERROR_WANT_READ\s0 may occur.
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This behaviour can be controlled with the \s-1SSL_MODE_AUTO_RETRY\s0 flag of the
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\&\fISSL_CTX_set_mode\fR\|(3) call.
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.PP
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If the underlying \s-1BIO\s0 is \fBnon-blocking\fR, \fISSL_write()\fR will also return,
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when the underlying \s-1BIO\s0 could not satisfy the needs of \fISSL_write()\fR
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to continue the operation. In this case a call to
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\&\fISSL_get_error\fR\|(3) with the
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return value of \fISSL_write()\fR will yield \fB\s-1SSL_ERROR_WANT_READ\s0\fR or
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\&\fB\s-1SSL_ERROR_WANT_WRITE\s0\fR. As at any time a re-negotiation is possible, a
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call to \fISSL_write()\fR can also cause read operations! The calling process
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then must repeat the call after taking appropriate action to satisfy the
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needs of \fISSL_write()\fR. The action depends on the underlying \s-1BIO\s0. When using a
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non-blocking socket, nothing is to be done, but \fIselect()\fR can be used to check
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for the required condition. When using a buffering \s-1BIO\s0, like a \s-1BIO\s0 pair, data
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must be written into or retrieved out of the \s-1BIO\s0 before being able to continue.
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.PP
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\&\fISSL_write()\fR will only return with success, when the complete contents
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of \fBbuf\fR of length \fBnum\fR has been written. This default behaviour
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can be changed with the \s-1SSL_MODE_ENABLE_PARTIAL_WRITE\s0 option of
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\&\fISSL_CTX_set_mode\fR\|(3). When this flag is set,
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\&\fISSL_write()\fR will also return with success, when a partial write has been
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successfully completed. In this case the \fISSL_write()\fR operation is considered
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completed. The bytes are sent and a new \fISSL_write()\fR operation with a new
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buffer (with the already sent bytes removed) must be started.
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A partial write is performed with the size of a message block, which is
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16kB for SSLv3/TLSv1.
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.SH "WARNING"
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.IX Header "WARNING"
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When an \fISSL_write()\fR operation has to be repeated because of
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\&\fB\s-1SSL_ERROR_WANT_READ\s0\fR or \fB\s-1SSL_ERROR_WANT_WRITE\s0\fR, it must be repeated
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with the same arguments.
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.PP
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When calling \fISSL_write()\fR with num=0 bytes to be sent the behaviour is
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undefined.
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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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.IX Item ">0"
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The write operation was successful, the return value is the number of
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bytes actually written to the \s-1TLS/SSL\s0 connection.
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.IP "0" 4
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The write operation was not successful. Probably the underlying connection
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was closed. Call \fISSL_get_error()\fR with the return value \fBret\fR to find out,
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whether an error occurred or the connection was shut down cleanly
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(\s-1SSL_ERROR_ZERO_RETURN\s0).
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.Sp
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SSLv2 (deprecated) does not support a shutdown alert protocol, so it can
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only be detected, whether the underlying connection was closed. It cannot
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be checked, why the closure happened.
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.IP "<0" 4
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.IX Item "<0"
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The write operation was not successful, because either an error occurred
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or action must be taken by the calling process. Call \fISSL_get_error()\fR with the
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return value \fBret\fR 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_read\fR\|(3),
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\&\fISSL_CTX_set_mode\fR\|(3), \fISSL_CTX_new\fR\|(3),
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\&\fISSL_connect\fR\|(3), \fISSL_accept\fR\|(3)
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\&\fISSL_set_connect_state\fR\|(3),
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\&\fIssl\fR\|(3), \fIbio\fR\|(3)
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