BIO_push.pod revision 279265 
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:
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41 BIO_push(b64, f);
42
43is made then the new chain will be B<b64-f>. After making the calls
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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);
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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