=head1 NAME
-BIO_s_bio, BIO_make_bio_pair, BIO_destroy_bio_pair, BIO_set_write_buf_size,
-BIO_get_write_buf_size, BIO_new_bio_pair, BIO_get_write_guarantee,
-BIO_ctrl_get_write_guarantee, BIO_get_read_request, BIO_ctrl_get_read_request,
-BIO_ctrl_reset_read_request - BIO pair BIO
+BIO_s_bio, BIO_make_bio_pair, BIO_destroy_bio_pair, BIO_shutdown_wr,
+BIO_set_write_buf_size, BIO_get_write_buf_size, BIO_new_bio_pair,
+BIO_get_write_guarantee, BIO_ctrl_get_write_guarantee, BIO_get_read_request,
+BIO_ctrl_get_read_request, BIO_ctrl_reset_read_request - BIO pair BIO
=head1 SYNOPSIS
#define BIO_make_bio_pair(b1,b2) (int)BIO_ctrl(b1,BIO_C_MAKE_BIO_PAIR,0,b2)
#define BIO_destroy_bio_pair(b) (int)BIO_ctrl(b,BIO_C_DESTROY_BIO_PAIR,0,NULL)
+ #define BIO_shutdown_wr(b) (int)BIO_ctrl(b, BIO_C_SHUTDOWN_WR, 0, NULL)
+
#define BIO_set_write_buf_size(b,size) (int)BIO_ctrl(b,BIO_C_SET_WRITE_BUF_SIZE,size,NULL)
#define BIO_get_write_buf_size(b,size) (size_t)BIO_ctrl(b,BIO_C_GET_WRITE_BUF_SIZE,size,NULL)
BIO_destroy_pair() destroys the association between two connected BIOs. Freeing
up any half of the pair will automatically destroy the association.
+BIO_shutdown_wr() is used to close down a BIO B<b>. After this call no further
+writes on BIO B<b> are allowed (they will return an error). Reads on the other
+half of the pair will return any pending data or EOF when all pending data has
+been read.
+
BIO_set_write_buf_size() sets the write buffer size of BIO B<b> to B<size>.
If the size is not initialized a default value is used. This is currently
17K, sufficient for a maximum size TLS record.
BIO_new_bio_pair() combines the calls to BIO_new(), BIO_make_bio_pair() and
BIO_set_write_buf_size() to create a connected pair of BIOs B<bio1>, B<bio2>
with write buffer sizes B<writebuf1> and B<writebuf2>. If either size is
-zero then the default size is used.
+zero then the default size is used. BIO_new_bio_pair() does not check whether
+B<bio1> or B<bio2> do point to some other BIO, the values are overwritten,
+BIO_free() is not called.
BIO_get_write_guarantee() and BIO_ctrl_get_write_guarantee() return the maximum
length of data that can be currently written to the BIO. Writes larger than this
before flushing the write buffer it will never succeed because the request was
never sent!
+=head1 RETURN VALUES
+
+BIO_new_bio_pair() returns 1 on success, with the new BIOs available in
+B<bio1> and B<bio2>, or 0 on failure, with NULL pointers stored into the
+locations for B<bio1> and B<bio2>. Check the error stack for more information.
+
+[XXXXX: More return values need to be added here]
+
=head1 EXAMPLE
-TBA
+The BIO pair can be used to have full control over the network access of an
+application. The application can call select() on the socket as required
+without having to go through the SSL-interface.
+
+ BIO *internal_bio, *network_bio;
+ ...
+ BIO_new_bio_pair(internal_bio, 0, network_bio, 0);
+ SSL_set_bio(ssl, internal_bio, internal_bio);
+ SSL_operations();
+ ...
+
+ application | TLS-engine
+ | |
+ +----------> SSL_operations()
+ | /\ ||
+ | || \/
+ | BIO-pair (internal_bio)
+ +----------< BIO-pair (network_bio)
+ | |
+ socket |
+
+ ...
+ SSL_free(ssl); /* implicitly frees internal_bio */
+ BIO_free(network_bio);
+ ...
+
+As the BIO pair will only buffer the data and never directly access the
+connection, it behaves non-blocking and will return as soon as the write
+buffer is full or the read buffer is drained. Then the application has to
+flush the write buffer and/or fill the read buffer.
+
+Use the BIO_ctrl_pending(), to find out whether data is buffered in the BIO
+and must be transfered to the network. Use BIO_ctrl_get_read_request() to
+find out, how many bytes must be written into the buffer before the
+SSL_operation() can successfully be continued.
+
+=head1 WARNING
+
+As the data is buffered, SSL_operation() may return with a ERROR_SSL_WANT_READ
+condition, but there is still data in the write buffer. An application must
+not rely on the error value of SSL_operation() but must assure that the
+write buffer is always flushed first. Otherwise a deadlock may occur as
+the peer might be waiting for the data before being able to continue.
=head1 SEE ALSO