165 lines
6.8 KiB
Plaintext
165 lines
6.8 KiB
Plaintext
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=pod
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=head1 NAME
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SSL_write_ex, SSL_write, SSL_sendfile - write bytes to a TLS/SSL connection
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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ossl_ssize_t SSL_sendfile(SSL *s, int fd, off_t offset, size_t size, int flags);
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int SSL_write_ex(SSL *s, const void *buf, size_t num, size_t *written);
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int SSL_write(SSL *ssl, const void *buf, int num);
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=head1 DESCRIPTION
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SSL_write_ex() and SSL_write() write B<num> bytes from the buffer B<buf> into
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the specified B<ssl> connection. On success SSL_write_ex() will store the number
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of bytes written in B<*written>.
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SSL_sendfile() writes B<size> bytes from offset B<offset> in the file
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descriptor B<fd> to the specified SSL connection B<s>. This function provides
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efficient zero-copy semantics. SSL_sendfile() is available only when
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Kernel TLS is enabled, which can be checked by calling BIO_get_ktls_send().
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It is provided here to allow users to maintain the same interface.
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The meaning of B<flags> is platform dependent.
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Currently, under Linux it is ignored.
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=head1 NOTES
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In the paragraphs below a "write function" is defined as one of either
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SSL_write_ex(), or SSL_write().
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If necessary, a write function will negotiate a TLS/SSL session, if not already
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explicitly performed by L<SSL_connect(3)> or L<SSL_accept(3)>. If the peer
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requests a re-negotiation, it will be performed transparently during
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the write function operation. The behaviour of the write functions depends on the
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underlying BIO.
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For the transparent negotiation to succeed, the B<ssl> must have been
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initialized to client or server mode. This is being done by calling
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L<SSL_set_connect_state(3)> or SSL_set_accept_state()
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before the first call to a write function.
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If the underlying BIO is B<blocking>, the write functions will only return, once
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the write operation has been finished or an error occurred.
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If the underlying BIO is B<nonblocking> the write functions will also return
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when the underlying BIO could not satisfy the needs of the function to continue
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the operation. In this case a call to L<SSL_get_error(3)> with the
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return value of the write function will yield B<SSL_ERROR_WANT_READ>
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or B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a
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call to a write function can also cause read operations! The calling process
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then must repeat the call after taking appropriate action to satisfy the needs
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of the write function. The action depends on the underlying BIO. When using a
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nonblocking socket, nothing is to be done, but select() can be used to check
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for the required condition. When using a buffering BIO, like a BIO pair, data
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must be written into or retrieved out of the BIO before being able to continue.
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The write functions will only return with success when the complete contents of
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B<buf> of length B<num> has been written. This default behaviour can be changed
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with the SSL_MODE_ENABLE_PARTIAL_WRITE option of L<SSL_CTX_set_mode(3)>. When
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this flag is set the write functions will also return with success when a
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partial write has been successfully completed. In this case the write function
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operation is considered completed. The bytes are sent and a new write call with
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a new buffer (with the already sent bytes removed) must be started. A partial
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write is performed with the size of a message block, which is 16kB.
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When used with a QUIC SSL object, calling an I/O function such as SSL_write()
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allows internal network event processing to be performed. It is important that
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this processing is performed regularly. If an application is not using thread
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assisted mode, an application should ensure that an I/O function such as
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SSL_write() is called regularly, or alternatively ensure that SSL_handle_events()
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is called regularly. See L<openssl-quic(7)> and L<SSL_handle_events(3)> for more
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information.
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=head1 WARNINGS
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When a write function call has to be repeated because L<SSL_get_error(3)>
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returned B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated
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with the same arguments.
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The data that was passed might have been partially processed.
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When B<SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER> was set using L<SSL_CTX_set_mode(3)>
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the pointer can be different, but the data and length should still be the same.
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You should not call SSL_write() with num=0, it will return an error.
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SSL_write_ex() can be called with num=0, but will not send application data to
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the peer.
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=head1 RETURN VALUES
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SSL_write_ex() will return 1 for success or 0 for failure. Success means that
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all requested application data bytes have been written to the SSL connection or,
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if SSL_MODE_ENABLE_PARTIAL_WRITE is in use, at least 1 application data byte has
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been written to the SSL connection. Failure means that not all the requested
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bytes have been written yet (if SSL_MODE_ENABLE_PARTIAL_WRITE is not in use) or
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no bytes could be written to the SSL connection (if
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SSL_MODE_ENABLE_PARTIAL_WRITE is in use). Failures can be retryable (e.g. the
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network write buffer has temporarily filled up) or non-retryable (e.g. a fatal
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network error). In the event of a failure call L<SSL_get_error(3)> to find out
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the reason which indicates whether the call is retryable or not.
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For SSL_write() the following return values can occur:
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=over 4
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=item E<gt> 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 TLS/SSL connection.
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=item Z<><= 0
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The write operation was not successful, because either the connection was
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closed, an error occurred or action must be taken by the calling process.
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Call SSL_get_error() with the return value B<ret> to find out the reason.
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Old documentation indicated a difference between 0 and -1, and that -1 was
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retryable.
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You should instead call SSL_get_error() to find out if it's retryable.
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=back
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For SSL_sendfile(), the following return values can occur:
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=over 4
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=item Z<>>= 0
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The write operation was successful, the return value is the number
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of bytes of the file written to the TLS/SSL connection. The return
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value can be less than B<size> for a partial write.
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=item E<lt> 0
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The write operation was not successful, because either the connection was
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closed, an error occurred or action must be taken by the calling process.
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Call SSL_get_error() with the return value to find out the reason.
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=back
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=head1 SEE ALSO
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L<SSL_get_error(3)>, L<SSL_read_ex(3)>, L<SSL_read(3)>
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L<SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)>,
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L<SSL_connect(3)>, L<SSL_accept(3)>
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L<SSL_set_connect_state(3)>, L<BIO_ctrl(3)>,
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L<ssl(7)>, L<bio(7)>
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=head1 HISTORY
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The SSL_write_ex() function was added in OpenSSL 1.1.1.
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The SSL_sendfile() function was added in OpenSSL 3.0.
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=head1 COPYRIGHT
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Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). 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 LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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