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authorschwarze <>2015-02-16 16:42:14 +0000
committerschwarze <>2015-02-16 16:42:14 +0000
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third batch of perlpod(1) to mdoc(7) conversion
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1.Dd $Mdocdate: February 16 2015 $
2.Dt BIO_SET_CALLBACK 3
3.Os
4.Sh NAME
5.Nm BIO_set_callback ,
6.Nm BIO_get_callback ,
7.Nm BIO_set_callback_arg ,
8.Nm BIO_get_callback_arg ,
9.Nm BIO_debug_callback
10.Nd BIO callback functions
11.Sh SYNOPSIS
12.In openssl/bio.h
13.Fd #define BIO_set_callback(b,cb) ((b)->callback=(cb))
14.Fd #define BIO_get_callback(b) ((b)->callback)
15.Fd #define BIO_set_callback_arg(b,arg) ((b)->cb_arg=(char *)(arg))
16.Fd #define BIO_get_callback_arg(b) ((b)->cb_arg)
17.Ft long
18.Fo BIO_debug_callback
19.Fa "BIO *bio"
20.Fa "int cmd"
21.Fa "const char *argp"
22.Fa "int argi"
23.Fa "long argl"
24.Fa "long ret"
25.Fc
26.Ft typedef long *
27.Fo callback
28.Fa "BIO *b"
29.Fa "int oper"
30.Fa "const char *argp"
31.Fa "int argi"
32.Fa "long argl"
33.Fa "long retvalue"
34.Fc
35.Sh DESCRIPTION
36.Fn BIO_set_callback
37and
38.Fn BIO_get_callback
39set and retrieve the BIO callback, they are both macros.
40The callback is called during most high level BIO operations.
41It can be used for debugging purposes to trace operations on a BIO
42or to modify its operation.
43.Pp
44.Fn BIO_set_callback_arg
45and
46.Fn BIO_get_callback_arg
47are macros which can be used to set and retrieve an argument
48for use in the callback.
49.Pp
50.Fn BIO_debug_callback
51is a standard debugging callback which prints
52out information relating to each BIO operation.
53If the callback argument is set, it is interpreted as a BIO
54to send the information to, otherwise stderr is used.
55.Pp
56.Fn callback
57is the callback function itself.
58The meaning of each argument is described below.
59.Pp
60The BIO the callback is attached to is passed in
61.Fa b .
62.Pp
63.Fa oper
64is set to the operation being performed.
65For some operations the callback is called twice,
66once before and once after the actual operation.
67The latter case has
68.Fa oper
69or'ed with
70.Dv BIO_CB_RETURN .
71.Pp
72The meaning of the arguments
73.Fa argp ,
74.Fa argi
75and
76.Fa argl
77depends on the value of
78.Fa oper ,
79that is the operation being performed.
80.Pp
81.Fa retvalue
82is the return value that would be returned to the application
83if no callback were present.
84The actual value returned is the return value of the callback itself.
85In the case of callbacks called before the actual BIO operation,
861 is placed in retvalue.
87If the return value is not positive, it will be immediately returned to
88the application and the BIO operation will not be performed.
89.Pp
90The callback should normally simply return
91.Fa retvalue
92when it has finished processing, unless it specifically wishes
93to modify the value returned to the application.
94.Ss Callback operations
95.Bl -tag -width Ds
96.It Fn BIO_free b
97.Fn callback b BIO_CB_FREE NULL 0L 0L 1L
98is called before the free operation.
99.It Fn BIO_read b out outl
100.Fn callback b BIO_CB_READ out outl 0L 1L
101is called before the read and
102.Fn callback b BIO_CB_READ|BIO_CB_RETURN out outl 0L retvalue
103after.
104.It Fn BIO_write b in inl
105.Fn callback b BIO_CB_WRITE in inl 0L 1L
106is called before the write and
107.Fn callback b BIO_CB_WRITE|BIO_CB_RETURN in inl 0L retvalue
108after.
109.It Fn BIO_gets b out outl
110.Fn callback b BIO_CB_GETS out outl 0L 1L
111is called before the operation and
112.Fn callback b BIO_CB_GETS|BIO_CB_RETURN out outl 0L retvalue
113after.
114.It Fn BIO_puts b in
115.Fn callback b BIO_CB_WRITE in 0 0L 1L
116is called before the operation and
117.Fn callback b BIO_CB_WRITE|BIO_CB_RETURN in 0 0L retvalue
118after.
119.It Fn BIO_ctrl b cmd larg parg
120.Fn callback b BIO_CB_CTRL parg cmd larg 1L
121is called before the call and
122.Fn callback b BIO_CB_CTRL|BIO_CB_RETURN parg cmd larg ret
123after.
124.El
125.Sh EXAMPLES
126The
127.Fn BIO_debug_callback
128function is a good example, its source is in the file
129.Pa crypto/bio/bio_cb.c .