=head1 NAME
-SSL_read - Read bytes from a TLS connection.
+SSL_read - read bytes from a TLS/SSL connection.
=head1 SYNOPSIS
#include <openssl/ssl.h>
- int SSL_read(SSL *ssl, char *buf, int num);
+ int SSL_read(SSL *ssl, void *buf, int num);
=head1 DESCRIPTION
SSL_read() tries to read B<num> bytes from the specified B<ssl> into the
-buffer B<buf>. If necessary, SSL_read() will negotiate a TLS session, if
-not already explicitely performed by SSL_connect() or SSL_accept(). If the
+buffer B<buf>.
+
+=head1 NOTES
+
+If necessary, SSL_read() will negotiate a TLS/SSL session, if
+not already explicitly performed by L<SSL_connect(3)|SSL_connect(3)> or
+L<SSL_accept(3)|SSL_accept(3)>. 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.
+For the transparent negotiation to succeed, the B<ssl> must have been
+initialized to client or server mode. This is not the case if a generic
+method is being used (see L<SSL_CTX_new(3)|SSL_CTX_new(3)>, so that
+L<SSL_set_connect_state(3)|SSL_set_connect_state(3)> or SSL_set_accept_state()
+must be used before the first call to an SSL_read() or
+L<SSL_write(3)|SSL_write(3)> function.
+
+SSL_read() works based on the SSL/TLS records. The data are received in
+records (with a maximum record size of 16kB for SSLv3/TLSv1). Only when a
+record has been completely received, it can be processed (decryption and
+check of integrity). Therefore data that was not retrieved at the last
+call of SSL_read() can still be buffered inside the SSL layer and will be
+retrieved on the next call to SSL_read(). If B<num> is higher than the
+number of bytes buffered, SSL_read() will return with the bytes buffered.
+If no more bytes are in the buffer, SSL_read() will trigger the processing
+of the next record. Only when the record has been received and processed
+completely, SSL_read() will return reporting success. At most the contents
+of the record will be returned.
+
If the underlying BIO is B<blocking>, SSL_read() will only return, once the
-read operation has been finished or an error occured.
+read operation has been finished or an error occurred, except when a
+renegotiation take place, in which case a SSL_ERROR_WANT_READ may occur.
+This behaviour can be controlled with the SSL_MODE_AUTO_RETRY flag of the
+L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)> call.
-If the underlying BIO is B<non-blocking>, SSL_read() will also return,
+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 SSL_ERROR_WANT_READ or
-SSL_ERROR_WANT_WRITE. As at any time a re-negotiation is possible, a
+to continue the operation. In this case a call to
+L<SSL_get_error(3)|SSL_get_error(3)> 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
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:
=item E<gt>0
-The read operation was successfull, the return value is the number of
-bytes actually read from the TLS connection.
+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 successfull, probably because no data was
+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 occured.
+whether an error occurred.
-=item -1
+=item E<lt>0
-The read operation was not successfull, because either an error occured
+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.
=head1 SEE ALSO
L<SSL_get_error(3)|SSL_get_error(3)>, L<SSL_write(3)|SSL_write(3)>,
+L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)>, L<SSL_CTX_new(3)|SSL_CTX_new(3)>,
+L<SSL_connect(3)|SSL_connect(3)>, L<SSL_accept(3)|SSL_accept(3)>
+L<SSL_set_connect_state(3)|SSL_set_connect_state(3)>,
L<ssl(3)|ssl(3)>, L<bio(3)|bio(3)>
=cut
projects / openssl.git / blobdiff