Edit File: SSL_write.3
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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" SSL_write \- write bytes to a TLS/SSL connection. .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& #include <openssl/ssl.h> \& \& int SSL_write(SSL *ssl, const void *buf, int num); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" \&\fBSSL_write()\fR writes \fBnum\fR bytes from the buffer \fBbuf\fR into the specified \&\fBssl\fR connection. .SH "NOTES" .IX Header "NOTES" If necessary, \fBSSL_write()\fR will negotiate a \s-1TLS/SSL\s0 session, if not already explicitly performed by \fBSSL_connect\fR\|(3) or \&\fBSSL_accept\fR\|(3). If the peer requests a re-negotiation, it will be performed transparently during the \fBSSL_write()\fR operation. The behaviour of \fBSSL_write()\fR depends on the underlying \s-1BIO.\s0 .PP For the transparent negotiation to succeed, the \fBssl\fR must have been initialized to client or server mode. This is being done by calling \&\fBSSL_set_connect_state\fR\|(3) or \fBSSL_set_accept_state()\fR before the first call to an \fBSSL_read\fR\|(3) or \fBSSL_write()\fR function. .PP If the underlying \s-1BIO\s0 is \fBblocking\fR, \fBSSL_write()\fR will only return, once the write operation has been finished or an error occurred, except when a renegotiation take place, in which case a \s-1SSL_ERROR_WANT_READ\s0 may occur. This behaviour can be controlled with the \s-1SSL_MODE_AUTO_RETRY\s0 flag of the \&\fBSSL_CTX_set_mode\fR\|(3) call. .PP If the underlying \s-1BIO\s0 is \fBnon-blocking\fR, \fBSSL_write()\fR will also return, when the underlying \s-1BIO\s0 could not satisfy the needs of \fBSSL_write()\fR to continue the operation. In this case a call to \&\fBSSL_get_error\fR\|(3) with the return value of \fBSSL_write()\fR will yield \fB\s-1SSL_ERROR_WANT_READ\s0\fR or \&\fB\s-1SSL_ERROR_WANT_WRITE\s0\fR. As at any time a re-negotiation is possible, a call to \fBSSL_write()\fR can also cause read operations! The calling process then must repeat the call after taking appropriate action to satisfy the needs of \fBSSL_write()\fR. The action depends on the underlying \s-1BIO.\s0 When using a non-blocking socket, nothing is to be done, but \fBselect()\fR can be used to check for the required condition. When using a buffering \s-1BIO,\s0 like a \s-1BIO\s0 pair, data must be written into or retrieved out of the \s-1BIO\s0 before being able to continue. .PP \&\fBSSL_write()\fR will only return with success, when the complete contents of \fBbuf\fR of length \fBnum\fR has been written. This default behaviour can be changed with the \s-1SSL_MODE_ENABLE_PARTIAL_WRITE\s0 option of \&\fBSSL_CTX_set_mode\fR\|(3). When this flag is set, \&\fBSSL_write()\fR will also return with success, when a partial write has been successfully completed. In this case the \fBSSL_write()\fR operation is considered completed. The bytes are sent and a new \fBSSL_write()\fR operation with a new buffer (with the already sent bytes removed) must be started. A partial write is performed with the size of a message block, which is 16kB for SSLv3/TLSv1. .SH "WARNING" .IX Header "WARNING" When an \fBSSL_write()\fR operation has to be repeated because of \&\fB\s-1SSL_ERROR_WANT_READ\s0\fR or \fB\s-1SSL_ERROR_WANT_WRITE\s0\fR, it must be repeated with the same arguments. .PP When calling \fBSSL_write()\fR with num=0 bytes to be sent the behaviour is undefined. .SH "RETURN VALUES" .IX Header "RETURN VALUES" The following return values can occur: .IP "> 0" 4 .IX Item "> 0" The write operation was successful, the return value is the number of bytes actually written to the \s-1TLS/SSL\s0 connection. .IP "<= 0" 4 .IX Item "<= 0" The write operation was not successful, because either the connection was closed, an error occurred or action must be taken by the calling process. Call \fBSSL_get_error()\fR with the return value \fBret\fR to find out the reason. .Sp SSLv2 (deprecated) does not support a shutdown alert protocol, so it can only be detected, whether the underlying connection was closed. It cannot be checked, why the closure happened. .Sp Old documentation indicated a difference between 0 and \-1, and that \-1 was retryable. You should instead call \fBSSL_get_error()\fR to find out if it's retryable. .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBSSL_get_error\fR\|(3), \fBSSL_read\fR\|(3), \&\fBSSL_CTX_set_mode\fR\|(3), \fBSSL_CTX_new\fR\|(3), \&\fBSSL_connect\fR\|(3), \fBSSL_accept\fR\|(3) \&\fBSSL_set_connect_state\fR\|(3), \&\fBssl\fR\|(3), \fBbio\fR\|(3)