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=pod
=head1 NAME
SSL_read - read bytes from a TLS/SSL connection.
=head1 SYNOPSIS
#include <openssl/ssl.h>
int SSL_read(SSL *ssl, char *buf, int num);
=head1 DESCRIPTION
SSL_read() tries to read B<num> bytes from the specified B<ssl> into the
buffer B<buf>.
=head1 NOTES
If necessary, SSL_read() will negotiate a TLS/SSL session, if
not already explicitly performed by SSL_connect() or SSL_accept(). If the
peer requests a re-negotiation, it will be performed transparently during
the SSL_read() operation. The behaviour of SSL_read() depends on the
underlying BIO.
If the underlying BIO is B<blocking>, SSL_read() will only return, once the
read operation has been finished or an error occurred.
If the underlying BIO is B<non-blocking>, SSL_read() will also return
when the underlying BIO could not satisfy the needs of SSL_read()
to continue the operation. In this case a call to SSL_get_error() with the
return value of SSL_read() will yield B<SSL_ERROR_WANT_READ> or
B<SSL_ERROR_WANT_WRITE>. As at any time a re-negotiation is possible, a
call to SSL_read() can also cause write operations! The calling process
then must repeat the call after taking appropriate action to satisfy the
needs of SSL_read(). The action depends on the underlying BIO. When using a
non-blocking socket, nothing is to be done, but select() can be used to check
for the required condition. When using a buffering BIO, like a BIO pair, data
must be written into or retrieved out of the BIO before being able to continue.
=head1 WARNING
When an SSL_read() operation has to be repeated because of
B<SSL_ERROR_WANT_READ> or B<SSL_ERROR_WANT_WRITE>, it must be repeated
with the same arguments.
=head1 RETURN VALUES
The following return values can occur:
=over 4
=item E<gt>0
The read operation was successful; the return value is the number of
bytes actually read from the TLS/SSL connection.
=item 0
The read operation was not successful, probably because no data was
available. Call SSL_get_error() with the return value B<ret> to find out,
whether an error occurred.
=item -1
The read operation was not successful, because either an error occurred
or action must be taken by the calling process. Call SSL_get_error() with the
return value B<ret> to find out the reason.
=back
=head1 SEE ALSO
L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_write(3)|SSL_write(3)>,
L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)>
=cut
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