Edit File: SSL_write_ex.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_ex, SSL_write \- write bytes to a TLS/SSL connection .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& #include <openssl/ssl.h> \& \& int SSL_write_ex(SSL *s, const void *buf, size_t num, size_t *written); \& int SSL_write(SSL *ssl, const void *buf, int num); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" \&\fBSSL_write_ex()\fR and \fBSSL_write()\fR write \fBnum\fR bytes from the buffer \fBbuf\fR into the specified \fBssl\fR connection. On success \fBSSL_write_ex()\fR will store the number of bytes written in \fB*written\fR. .SH "NOTES" .IX Header "NOTES" In the paragraphs below a \*(L"write function\*(R" is defined as one of either \&\fBSSL_write_ex()\fR, or \fBSSL_write()\fR. .PP If necessary, a write function 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 write function operation. The behaviour of the write functions 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 a write function. .PP If the underlying \s-1BIO\s0 is \fBblocking\fR, the write functions will only return, once the write operation has been finished or an error occurred. .PP If the underlying \s-1BIO\s0 is \fBnonblocking\fR the write functions will also return when the underlying \s-1BIO\s0 could not satisfy the needs of the function to continue the operation. In this case a call to \fBSSL_get_error\fR\|(3) with the return value of the write function 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 a write function can also cause read operations! The calling process then must repeat the call after taking appropriate action to satisfy the needs of the write function. The action depends on the underlying \s-1BIO.\s0 When using a nonblocking 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 The write functions 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 the write functions will also return with success when a partial write has been successfully completed. In this case the write function operation is considered completed. The bytes are sent and a new write call 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. .SH "WARNINGS" .IX Header "WARNINGS" When a write function call has to be repeated because \fBSSL_get_error\fR\|(3) returned \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. The data that was passed might have been partially processed. When \fB\s-1SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER\s0\fR was set using \fBSSL_CTX_set_mode\fR\|(3) the pointer can be different, but the data and length should still be the same. .PP You should not call \fBSSL_write()\fR with num=0, it will return an error. \&\fBSSL_write_ex()\fR can be called with num=0, but will not send application data to the peer. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fBSSL_write_ex()\fR will return 1 for success or 0 for failure. Success means that all requested application data bytes have been written to the \s-1SSL\s0 connection or, if \s-1SSL_MODE_ENABLE_PARTIAL_WRITE\s0 is in use, at least 1 application data byte has been written to the \s-1SSL\s0 connection. Failure means that not all the requested bytes have been written yet (if \s-1SSL_MODE_ENABLE_PARTIAL_WRITE\s0 is not in use) or no bytes could be written to the \s-1SSL\s0 connection (if \&\s-1SSL_MODE_ENABLE_PARTIAL_WRITE\s0 is in use). Failures can be retryable (e.g. the network write buffer has temporarily filled up) or non-retryable (e.g. a fatal network error). In the event of a failure call \fBSSL_get_error\fR\|(3) to find out the reason which indicates whether the call is retryable or not. .PP For \fBSSL_write()\fR 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 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_ex\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\|(7), \fBbio\fR\|(7) .SH "HISTORY" .IX Header "HISTORY" The \fBSSL_write_ex()\fR function was added in OpenSSL 1.1.1. .SH "COPYRIGHT" .IX Header "COPYRIGHT" Copyright 2000\-2020 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>.