1*2175Sjp161948=pod 2*2175Sjp161948 3*2175Sjp161948=head1 NAME 4*2175Sjp161948 5*2175Sjp161948BIO_push, BIO_pop - add and remove BIOs from a chain. 6*2175Sjp161948 7*2175Sjp161948=head1 SYNOPSIS 8*2175Sjp161948 9*2175Sjp161948 #include <openssl/bio.h> 10*2175Sjp161948 11*2175Sjp161948 BIO * BIO_push(BIO *b,BIO *append); 12*2175Sjp161948 BIO * BIO_pop(BIO *b); 13*2175Sjp161948 14*2175Sjp161948=head1 DESCRIPTION 15*2175Sjp161948 16*2175Sjp161948The BIO_push() function appends the BIO B<append> to B<b>, it returns 17*2175Sjp161948B<b>. 18*2175Sjp161948 19*2175Sjp161948BIO_pop() removes the BIO B<b> from a chain and returns the next BIO 20*2175Sjp161948in the chain, or NULL if there is no next BIO. The removed BIO then 21*2175Sjp161948becomes a single BIO with no association with the original chain, 22*2175Sjp161948it can thus be freed or attached to a different chain. 23*2175Sjp161948 24*2175Sjp161948=head1 NOTES 25*2175Sjp161948 26*2175Sjp161948The names of these functions are perhaps a little misleading. BIO_push() 27*2175Sjp161948joins two BIO chains whereas BIO_pop() deletes a single BIO from a chain, 28*2175Sjp161948the deleted BIO does not need to be at the end of a chain. 29*2175Sjp161948 30*2175Sjp161948The process of calling BIO_push() and BIO_pop() on a BIO may have additional 31*2175Sjp161948consequences (a control call is made to the affected BIOs) any effects will 32*2175Sjp161948be noted in the descriptions of individual BIOs. 33*2175Sjp161948 34*2175Sjp161948=head1 EXAMPLES 35*2175Sjp161948 36*2175Sjp161948For these examples suppose B<md1> and B<md2> are digest BIOs, B<b64> is 37*2175Sjp161948a base64 BIO and B<f> is a file BIO. 38*2175Sjp161948 39*2175Sjp161948If the call: 40*2175Sjp161948 41*2175Sjp161948 BIO_push(b64, f); 42*2175Sjp161948 43*2175Sjp161948is made then the new chain will be B<b64-chain>. After making the calls 44*2175Sjp161948 45*2175Sjp161948 BIO_push(md2, b64); 46*2175Sjp161948 BIO_push(md1, md2); 47*2175Sjp161948 48*2175Sjp161948the new chain is B<md1-md2-b64-f>. Data written to B<md1> will be digested 49*2175Sjp161948by B<md1> and B<md2>, B<base64> encoded and written to B<f>. 50*2175Sjp161948 51*2175Sjp161948It should be noted that reading causes data to pass in the reverse 52*2175Sjp161948direction, that is data is read from B<f>, base64 B<decoded> and digested 53*2175Sjp161948by B<md1> and B<md2>. If the call: 54*2175Sjp161948 55*2175Sjp161948 BIO_pop(md2); 56*2175Sjp161948 57*2175Sjp161948The call will return B<b64> and the new chain will be B<md1-b64-f> data can 58*2175Sjp161948be written to B<md1> as before. 59*2175Sjp161948 60*2175Sjp161948=head1 RETURN VALUES 61*2175Sjp161948 62*2175Sjp161948BIO_push() returns the end of the chain, B<b>. 63*2175Sjp161948 64*2175Sjp161948BIO_pop() returns the next BIO in the chain, or NULL if there is no next 65*2175Sjp161948BIO. 66*2175Sjp161948 67*2175Sjp161948=head1 SEE ALSO 68*2175Sjp161948 69*2175Sjp161948TBA 70