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119 lines
4.5 KiB
Plaintext
119 lines
4.5 KiB
Plaintext
=pod
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=head1 NAME
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SSL_write_ex, SSL_write - 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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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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=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 functio 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, except when a
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renegotiation take place, in which case a SSL_ERROR_WANT_READ may occur.
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This behaviour can be controlled with the SSL_MODE_AUTO_RETRY flag of the
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L<SSL_CTX_set_mode(3)> call.
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If the underlying BIO is B<non-blocking> 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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non-blocking 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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=head1 WARNING
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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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When calling the write functions with num=0 bytes to be sent the behaviour is
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undefined.
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=head1 RETURN VALUES
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SSL_write_ex() will return 1 for success or 0 for failure. In the event of a
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failure call SSL_get_error() to find out the reason.
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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. Probably the underlying connection
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was closed. Call SSL_get_error() with the return value B<ret> to find out,
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whether an error occurred or the connection was shut down cleanly
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(SSL_ERROR_ZERO_RETURN).
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=item E<lt>0
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The write operation was not successful, because either an error occurred
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or action must be taken by the calling process. Call SSL_get_error() with the
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return value B<ret> 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)>,
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L<ssl(3)>, L<bio(3)>
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=head1 COPYRIGHT
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Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (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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