1=pod 2 3=head1 NAME 4 5SSL_write_ex, SSL_write, SSL_sendfile - write bytes to a TLS/SSL connection 6 7=head1 SYNOPSIS 8 9 #include <openssl/ssl.h> 10 11 ossl_ssize_t SSL_sendfile(SSL *s, int fd, off_t offset, size_t size, int flags); 12 int SSL_write_ex(SSL *s, const void *buf, size_t num, size_t *written); 13 int SSL_write(SSL *ssl, const void *buf, int num); 14 15=head1 DESCRIPTION 16 17SSL_write_ex() and SSL_write() write B<num> bytes from the buffer B<buf> into 18the specified B<ssl> connection. On success SSL_write_ex() will store the number 19of bytes written in B<*written>. 20 21SSL_sendfile() writes B<size> bytes from offset B<offset> in the file 22descriptor B<fd> to the specified SSL connection B<s>. This function provides 23efficient zero-copy semantics. SSL_sendfile() is available only when 24Kernel TLS is enabled, which can be checked by calling BIO_get_ktls_send(). 25It is provided here to allow users to maintain the same interface. 26The meaning of B<flags> is platform dependent. 27Currently, under Linux it is ignored. 28 29=head1 NOTES 30 31In the paragraphs below a "write function" is defined as one of either 32SSL_write_ex(), or SSL_write(). 33 34If necessary, a write function will negotiate a TLS/SSL session, if not already 35explicitly performed by L<SSL_connect(3)> or L<SSL_accept(3)>. If the peer 36requests a re-negotiation, it will be performed transparently during 37the write function operation. The behaviour of the write functions depends on the 38underlying BIO. 39 40For the transparent negotiation to succeed, the B<ssl> must have been 41initialized to client or server mode. This is being done by calling 42L<SSL_set_connect_state(3)> or SSL_set_accept_state() 43before the first call to a write function. 44 45If the underlying BIO is B<blocking>, the write functions will only return, once 46the write operation has been finished or an error occurred. 47 48If the underlying BIO is B<nonblocking> the write functions will also return 49when the underlying BIO could not satisfy the needs of the function to continue 50the operation. In this case a call to L<SSL_get_error(3)> with the 51return value of the write function will yield B<SSL_ERROR_WANT_READ> 52or B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a 53call to a write function can also cause read operations! The calling process 54then must repeat the call after taking appropriate action to satisfy the needs 55of the write function. The action depends on the underlying BIO. When using a 56nonblocking socket, nothing is to be done, but select() can be used to check 57for the required condition. When using a buffering BIO, like a BIO pair, data 58must be written into or retrieved out of the BIO before being able to continue. 59 60The write functions will only return with success when the complete contents of 61B<buf> of length B<num> has been written. This default behaviour can be changed 62with the SSL_MODE_ENABLE_PARTIAL_WRITE option of L<SSL_CTX_set_mode(3)>. When 63this flag is set the write functions will also return with success when a 64partial write has been successfully completed. In this case the write function 65operation is considered completed. The bytes are sent and a new write call with 66a new buffer (with the already sent bytes removed) must be started. A partial 67write is performed with the size of a message block, which is 16kB. 68 69=head1 WARNINGS 70 71When a write function call has to be repeated because L<SSL_get_error(3)> 72returned B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated 73with the same arguments. 74The data that was passed might have been partially processed. 75When B<SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER> was set using L<SSL_CTX_set_mode(3)> 76the pointer can be different, but the data and length should still be the same. 77 78You should not call SSL_write() with num=0, it will return an error. 79SSL_write_ex() can be called with num=0, but will not send application data to 80the peer. 81 82=head1 RETURN VALUES 83 84SSL_write_ex() will return 1 for success or 0 for failure. Success means that 85all requested application data bytes have been written to the SSL connection or, 86if SSL_MODE_ENABLE_PARTIAL_WRITE is in use, at least 1 application data byte has 87been written to the SSL connection. Failure means that not all the requested 88bytes have been written yet (if SSL_MODE_ENABLE_PARTIAL_WRITE is not in use) or 89no bytes could be written to the SSL connection (if 90SSL_MODE_ENABLE_PARTIAL_WRITE is in use). Failures can be retryable (e.g. the 91network write buffer has temporarily filled up) or non-retryable (e.g. a fatal 92network error). In the event of a failure call L<SSL_get_error(3)> to find out 93the reason which indicates whether the call is retryable or not. 94 95For SSL_write() the following return values can occur: 96 97=over 4 98 99=item E<gt> 0 100 101The write operation was successful, the return value is the number of 102bytes actually written to the TLS/SSL connection. 103 104=item Z<><= 0 105 106The write operation was not successful, because either the connection was 107closed, an error occurred or action must be taken by the calling process. 108Call SSL_get_error() with the return value B<ret> to find out the reason. 109 110Old documentation indicated a difference between 0 and -1, and that -1 was 111retryable. 112You should instead call SSL_get_error() to find out if it's retryable. 113 114=back 115 116For SSL_sendfile(), the following return values can occur: 117 118=over 4 119 120=item Z<>>= 0 121 122The write operation was successful, the return value is the number 123of bytes of the file written to the TLS/SSL connection. The return 124value can be less than B<size> for a partial write. 125 126=item E<lt> 0 127 128The write operation was not successful, because either the connection was 129closed, an error occurred or action must be taken by the calling process. 130Call SSL_get_error() with the return value to find out the reason. 131 132=back 133 134=head1 SEE ALSO 135 136L<SSL_get_error(3)>, L<SSL_read_ex(3)>, L<SSL_read(3)> 137L<SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)>, 138L<SSL_connect(3)>, L<SSL_accept(3)> 139L<SSL_set_connect_state(3)>, L<BIO_ctrl(3)>, 140L<ssl(7)>, L<bio(7)> 141 142=head1 HISTORY 143 144The SSL_write_ex() function was added in OpenSSL 1.1.1. 145The SSL_sendfile() function was added in OpenSSL 3.0. 146 147=head1 COPYRIGHT 148 149Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved. 150 151Licensed under the Apache License 2.0 (the "License"). You may not use 152this file except in compliance with the License. You can obtain a copy 153in the file LICENSE in the source distribution or at 154L<https://www.openssl.org/source/license.html>. 155 156=cut 157