mirror of https://github.com/openssl/openssl.git
210 lines
8.7 KiB
Plaintext
210 lines
8.7 KiB
Plaintext
=pod
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=head1 NAME
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SSL_write_ex2, SSL_write_ex, SSL_write, SSL_sendfile, SSL_WRITE_FLAG_CONCLUDE -
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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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#define SSL_WRITE_FLAG_CONCLUDE
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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_ex2(SSL *s, const void *buf, size_t num,
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uint64_t flags,
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size_t *written);
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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_write_ex2() functions similarly to SSL_write_ex() but can also accept
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optional flags which modify its behaviour. Calling SSL_write_ex2() with a
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I<flags> argument of 0 is exactly equivalent to calling SSL_write_ex().
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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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The I<flags> argument to SSL_write_ex2() can accept zero or more of the
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following flags. Note that which flags are supported will depend on the kind of
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SSL object and underlying protocol being used:
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=over 4
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=item B<SSL_WRITE_FLAG_CONCLUDE>
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This flag is only supported on QUIC stream SSL objects (or QUIC connection SSL
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objects with a default stream attached).
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If this flag is set, and the call to SSL_write_ex2() succeeds, and all of the
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data passed to the call is written (meaning that C<*written == num>), the
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relevant QUIC stream's send part is concluded automatically as though
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L<SSL_stream_conclude(3)> was called (causing transmission of a FIN for the
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stream).
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While using this flag is semantically equivalent to calling
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L<SSL_stream_conclude(3)> after a successful call to this function, using this
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flag enables greater efficiency than making these two API calls separately, as
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it enables the written stream data and the FIN flag indicating the end of the
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stream to be scheduled as part of the same QUIC STREAM frame and QUIC packet.
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Setting this flag does not cause a stream's send part to be concluded if not all
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of the data passed to the call was consumed.
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=back
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A call to SSL_write_ex2() fails if a flag is passed which is not supported or
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understood by the given SSL object. An application should determine if a flag is
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supported (for example, for B<SSL_WRITE_FLAG_CONCLUDE>, that a QUIC stream SSL
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object is being used) before attempting to use it.
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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() and SSL_write_ex2() return 1 for success or 0 for failure.
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Success means that all requested application data bytes have been written to the
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SSL connection or, if SSL_MODE_ENABLE_PARTIAL_WRITE is in use, at least 1
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application data byte has been written to the SSL connection. Failure means that
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not all the requested bytes have been written yet (if
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SSL_MODE_ENABLE_PARTIAL_WRITE is not in use) or no bytes could be written to the
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SSL connection (if SSL_MODE_ENABLE_PARTIAL_WRITE is in use). Failures can be
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retryable (e.g. the network write buffer has temporarily filled up) or
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non-retryable (e.g. a fatal network error). In the event of a failure call
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L<SSL_get_error(3)> to find out the reason which indicates whether the call is
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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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The SSL_write_ex2() function was added in OpenSSL 3.3.
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=head1 COPYRIGHT
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Copyright 2000-2024 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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