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