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BIO_new_bio_pair(3)
NAME
  BIO_new_bio_pair - Create a new BIO pair

SYNOPSIS
  #include <openssl/bio.h>

  int BIO_new_bio_pair(
	  BIO **bio1,
	  size_t writebuf1,
	  BIO **bio2,
	  size_t writebuf2 );

DESCRIPTION
  The BIO_new_bio_pair() function creates a buffering BIO pair. It has two
  endpoints between data can be buffered. Its typical use is to connect one
  endpoint as underlying input/output BIO to an SSL and access the other one
  controlled by the program instead of accessing the network connection
  directly.

  The two new BIOs, bio1 and bio2, are symmetric with respect to their
  functionality. The size of their buffers is determined by writebuf1 and
  writebuf2.  If the size given is 0, the default size is used.

  The BIO_new_bio_pair() function does not check whether bio1 or bio2 point
  to another BIO. The values are overwritten, and the BIO_free() function is
  not called.

  The two BIOs, even though forming a BIO pair, must be freed separately,
  using the BIO_free() function. This is important because some SSL
  functions, such as SSL_set_bio() and SSL_free(), call BIO_free()
  implicitly, so that the peer-BIO is left untouched and also must be freed
  using BIO_free().

NOTES
  As the data is buffered, the SSL_operation() function might return an
  ERROR_SSL_WANT_READ condition, but there is still data in the write buffer.
  An application must not rely on the error value of the SSL_operation()
  function, 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.

RETURN VALUES
  The following return values can occur:

    ·  1

       The BIO pair was created successfully. The new BIOs are available in
       bio1 and bio2.

    ·  0

       The operation failed. The NULL pointer is stored into the locations
       for bio1 and bio2. Check the error stack for more information.

EXAMPLE
  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);
	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() function to find out whether data is buffered in
  the BIO and must be transfered to the network. Use the
  BIO_ctrl_get_read_request() function to find out how many bytes must be
  written into the buffer before the SSL_operation() can continue.

SEE ALSO
  Functions: SSL_set_bio(3), ssl(3), bio(3), BIO_ctrl_pending(3),
  BIO_ctrl_get_read_request(3)

Index for Section 3

Alphabetical listing for B

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