107 lines
4.0 KiB
Plaintext
107 lines
4.0 KiB
Plaintext
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=pod
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=head1 NAME
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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(SSL *ssl, const void *buf, int num);
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=head1 DESCRIPTION
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SSL_write() writes B<num> bytes from the buffer B<buf> into the specified
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B<ssl> connection.
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=head1 NOTES
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If necessary, SSL_write() will negotiate a TLS/SSL session, if
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not already explicitly performed by L<SSL_connect(3)|SSL_connect(3)> or
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L<SSL_accept(3)|SSL_accept(3)>. If the
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peer requests a re-negotiation, it will be performed transparently during
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the SSL_write() operation. The behaviour of SSL_write() 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)|SSL_set_connect_state(3)> or SSL_set_accept_state()
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before the first call to an L<SSL_read(3)|SSL_read(3)> or SSL_write() function.
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If the underlying BIO is B<blocking>, SSL_write() will only return, once the
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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)|SSL_CTX_set_mode(3)> call.
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If the underlying BIO is B<non-blocking>, SSL_write() will also return,
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when the underlying BIO could not satisfy the needs of SSL_write()
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to continue the operation. In this case a call to
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L<SSL_get_error(3)|SSL_get_error(3)> with the
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return value of SSL_write() will yield B<SSL_ERROR_WANT_READ> or
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B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a
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call to SSL_write() can also cause read operations! The calling process
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then must repeat the call after taking appropriate action to satisfy the
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needs of SSL_write(). 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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SSL_write() will only return with success, when the complete contents
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of B<buf> of length B<num> has been written. This default behaviour
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can be changed with the SSL_MODE_ENABLE_PARTIAL_WRITE option of
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L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>. When this flag is set,
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SSL_write() will also return with success, when a partial write has been
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successfully completed. In this case the SSL_write() operation is considered
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completed. The bytes are sent and a new SSL_write() operation with a new
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buffer (with the already sent bytes removed) must be started.
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A partial write is performed with the size of a message block, which is
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16kB for SSLv3/TLSv1.
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=head1 WARNING
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When an SSL_write() operation has to be repeated because of
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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 SSL_write() 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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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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SSLv2 (deprecated) does not support a shutdown alert protocol, so it can
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only be detected, whether the underlying connection was closed. It cannot
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be checked, why the closure happened.
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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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=head1 SEE ALSO
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L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_read(3)|SSL_read(3)>,
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L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)|SSL_CTX_new(3)>,
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L<SSL_connect(3)|SSL_connect(3)>, L<SSL_accept(3)|SSL_accept(3)>
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L<SSL_set_connect_state(3)|SSL_set_connect_state(3)>,
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L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)>
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=cut
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