=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_s_bio() returns the method for a BIO pair. A BIO pair is a pair of source/sink
BIOs where data written to either half of the pair is buffered and can be read from
-the other half.
+the other half. Both halves must usually by handled by the same application thread
+since no locking is done on the internal data structures.
Since BIO chains typically end in a source/sink BIO it is possible to make this
one half of a BIO pair and have all the data processed by the chain under application
control.
-One typical use of BIO pairs is to place SSL I/O under application control, this
-can be used when the application wishes to use a non standard trasport for
-SSL or the normal socket routines are inappropriate.
+One typical use of BIO pairs is to place TLS/SSL I/O under application control, this
+can be used when the application wishes to use a non standard transport for
+TLS/SSL or the normal socket routines are inappropriate.
Calls to BIO_read() will read data from the buffer or request a retry if no
data is available.
BIO_make_bio_pair() joins two separate BIOs into a connected pair.
BIO_destroy_pair() destroys the association between two connected BIOs. Freeing
-up both halves of the pair will automatically destroy the association.
+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 initialised a default value is used. This is currently
+If the size is not initialized a default value is used. This is currently
17K, sufficient for a maximum size TLS record.
BIO_get_write_buf_size() returns the size of the write buffer.
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_guarentee() return the maximum
+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
value will return a value from BIO_write() less than the amount requested or if the
buffer is full request a retry. BIO_ctrl_get_write_guarantee() is a function
whereas BIO_get_write_guarantee() is a macro.
-BIO_get_read_request() and BIO_ctrl_get_read_request() return the amount of data
-requested (or the buffer size if it is less) if the last read failed due to an
-empty buffer. This can be used to determine how much data should be written to the
-other half of the pair so the next read will succeed: this is most useful in SSL
-applications where the amount of data read is usually meaningful rather than just
-a buffer size. After a successful read this call will return zero.
+BIO_get_read_request() and BIO_ctrl_get_read_request() return the
+amount of data requested, or the buffer size if it is less, if the
+last read attempt at the other half of the BIO pair failed due to an
+empty buffer. This can be used to determine how much data should be
+written to the BIO so the next read will succeed: this is most useful
+in TLS/SSL applications where the amount of data read is usually
+meaningful rather than just a buffer size. After a successful read
+this call will return zero. It also will return zero once new data
+has been written satisfying the read request or part of it.
+Note that BIO_get_read_request() never returns an amount larger
+than that returned by BIO_get_write_guarantee().
BIO_ctrl_reset_read_request() can also be used to reset the value returned by
BIO_get_read_request() to zero.
=head1 NOTES
-Both halves of a BIO pair should be freed. That is even if one half is implicity
+Both halves of a BIO pair should be freed. That is even if one half is implicit
freed due to a BIO_free_all() or SSL_free() call the other half needs to be freed.
-When used in bidirectional applications (such as SSL) care should be taken to
+When used in bidirectional applications (such as TLS/SSL) care should be taken to
flush any data in the write buffer. This can be done by calling BIO_pending()
on the other half of the pair and, if any data is pending, reading it and sending
it to the underlying transport. This must be done before any normal processing
To see why this is important consider a case where a request is sent using
BIO_write() and a response read with BIO_read(), this can occur during an
-SSL handshake for example. BIO_write() will succeed and place data in the write
+TLS/SSL handshake for example. BIO_write() will succeed and place data in the write
buffer. BIO_read() will initially fail and BIO_should_read() will be true. If
the application then waits for data to be available on the underlying transport
-before flusing the write buffer it will never succeed because the request was
+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 transferred 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
projects / openssl.git / blobdiff