BIOsbio(3) OpenSSL BIOsbio(3)

NAME
       BIOsbio, BIOmakebiopair, BIOdestroybiopair, BIOshutdownwr,
       BIOsetwritebufsize, BIOgetwritebufsize, BIOnewbiopair,
       BIOgetwriteguarantee, BIOctrlgetwriteguarantee,
       BIOgetreadrequest, BIOctrlgetreadrequest,
       BIOctrlresetreadrequest - BIO pair BIO

SYNOPSIS
        #include 

        BIOMETHOD *BIOsbio(void);

        #define BIOmakebiopair(b1,b2)   (int)BIOctrl(b1,BIOCMAKEBIOPAIR,0,b2)
        #define BIOdestroybiopair(b)    (int)BIOctrl(b,BIOCDESTROYBIOPAIR,0,NULL)

        #define BIOshutdownwr(b) (int)BIOctrl(b, BIOCSHUTDOWNWR, 0, NULL)

        #define BIOsetwritebufsize(b,size) (int)BIOctrl(b,BIOCSETWRITEBUFSIZE,size,NULL)
        #define BIOgetwritebufsize(b,size) (sizet)BIOctrl(b,BIOCGETWRITEBUFSIZE,size,NULL)

        int BIOnewbiopair(BIO **bio1, sizet writebuf1, BIO **bio2, sizet writebuf2);

        #define BIOgetwriteguarantee(b) (int)BIOctrl(b,BIOCGETWRITEGUARANTEE,0,NULL)
        sizet BIOctrlgetwriteguarantee(BIO *b);

        #define BIOgetreadrequest(b)    (int)BIOctrl(b,BIOCGETREADREQUEST,0,NULL)
        sizet BIOctrlgetreadrequest(BIO *b);

        int BIOctrlresetreadrequest(BIO *b);

DESCRIPTION
       BIOsbio() 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. 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 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 BIOread() will read data from the buffer or request a retry
       if no data is available.

       Calls to BIOwrite() will place data in the buffer or request a retry
       if the buffer is full.

       The standard calls BIOctrlpending() and BIOctrlwpending() can be
       used to determine the amount of pending data in the read or write
       buffer.

       BIOreset() clears any data in the write buffer.

       BIOmakebiopair() joins two separate BIOs into a connected pair.

       BIOdestroypair() destroys the association between two connected BIOs.
       Freeing up any half of the pair will automatically destroy the
       association.

       BIOshutdownwr() is used to close down a BIO bb. After this call no
       further writes on BIO bb 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.

       BIOsetwritebufsize() sets the write buffer size of BIO bb to ssiizzee.
       If the size is not initialized a default value is used. This is
       currently 17K, sufficient for a maximum size TLS record.

       BIOgetwritebufsize() returns the size of the write buffer.

       BIOnewbiopair() combines the calls to BIOnew(), BIOmakebiopair()
       and BIOsetwritebufsize() to create a connected pair of BIOs bbiioo11,
       bbiioo22 with write buffer sizes wwrriitteebbuuff11 and wwrriitteebbuuff22. If either size is
       zero then the default size is used.  BIOnewbiopair() does not check
       whether bbiioo11 or bbiioo22 do point to some other BIO, the values are
       overwritten, BIOfree() is not called.

       BIOgetwriteguarantee() and BIOctrlgetwriteguarantee() return the
       maximum length of data that can be currently written to the BIO. Writes
       larger than this value will return a value from BIOwrite() less than
       the amount requested or if the buffer is full request a retry.
       BIOctrlgetwriteguarantee() is a function whereas
       BIOgetwriteguarantee() is a macro.

       BIOgetreadrequest() and BIOctrlgetreadrequest() 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
       BIOgetreadrequest() never returns an amount larger than that
       returned by BIOgetwriteguarantee().

       BIOctrlresetreadrequest() can also be used to reset the value
       returned by BIOgetreadrequest() to zero.

NNOOTTEESS
       Both halves of a BIO pair should be freed. That is even if one half is
       implicit freed due to a BIOfreeall() or SSLfree() call the other
       half needs to be freed.

       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 BIOpending() 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 (such as calling select() )
       due to a request and BIOshouldread() being true.

       To see why this is important consider a case where a request is sent
       using BIOwrite() and a response read with BIOread(), this can occur
       during an TLS/SSL handshake for example. BIOwrite() will succeed and
       place data in the write buffer. BIOread() will initially fail and
       BIOshouldread() will be true. If the application then waits for data
       to be available on the underlying transport before flushing the write
       buffer it will never succeed because the request was never sent!

RETURN VALUES
       BIOnewbiopair() returns 1 on success, with the new BIOs available in
       bbiioo11 and bbiioo22, or 0 on failure, with NULL pointers stored into the
       locations for bbiioo11 and bbiioo22. Check the error stack for more
       information.

       [XXXXX: More return values need to be added here]

EEXXAAMMPPLLEE
       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 *internalbio, *networkbio;
        ...
        BIOnewbiopair(internalbio, 0, networkbio, 0);
        SSLsetbio(ssl, internalbio, internalbio);
        SSLoperations();
        ...

        application |   TLS-engine
           |        |
           +-----> SSLoperations()
                    |     /\    ||
                    |     ||    \/
                    |   BIO-pair (internalbio)
           +-----< BIO-pair (networkbio)
           |        |
         socket     |

         ...
         SSLfree(ssl);                /* implicitly frees internalbio */
         BIOfree(networkbio);
         ...

       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 BIOctrlpending(), to find out whether data is buffered in the
       BIO and must be transfered to the network. Use
       BIOctrlgetreadrequest() to find out, how many bytes must be written
       into the buffer before the SSLoperation() can successfully be
       continued.

WWAARRNNIINNGG
       As the data is buffered, SSLoperation() may return with a
       ERRORSSLWANTREAD condition, but there is still data in the write
       buffer. An application must not rely on the error value of
       SSLoperation() 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.

SEE ALSO
       SSLsetbio(3), ssl(3), bio(3), BIOshouldretry(3), BIOread(3)



0.9.7l                            2002-12-12                      BIOsbio(3)