1=pod
2
3=head1 NAME
4
5BIO_ctrl, BIO_callback_ctrl, BIO_ptr_ctrl, BIO_int_ctrl, BIO_reset,
6BIO_seek, BIO_tell, BIO_flush, BIO_eof, BIO_set_close, BIO_get_close,
7BIO_pending, BIO_wpending, BIO_ctrl_pending, BIO_ctrl_wpending,
8BIO_get_info_callback, BIO_set_info_callback - BIO control operations
9
10=head1 SYNOPSIS
11
12 #include <openssl/bio.h>
13
14 long BIO_ctrl(BIO *bp,int cmd,long larg,void *parg);
15 long BIO_callback_ctrl(BIO *b, int cmd, void (*fp)(struct bio_st *, int, const char *, int, long, long));
16 char *	BIO_ptr_ctrl(BIO *bp,int cmd,long larg);
17 long BIO_int_ctrl(BIO *bp,int cmd,long larg,int iarg);
18
19 int BIO_reset(BIO *b);
20 int BIO_seek(BIO *b, int ofs);
21 int BIO_tell(BIO *b);
22 int BIO_flush(BIO *b);
23 int BIO_eof(BIO *b);
24 int BIO_set_close(BIO *b,long flag);
25 int BIO_get_close(BIO *b);
26 int BIO_pending(BIO *b);
27 int BIO_wpending(BIO *b);
28 size_t BIO_ctrl_pending(BIO *b);
29 size_t BIO_ctrl_wpending(BIO *b);
30
31 int BIO_get_info_callback(BIO *b,bio_info_cb **cbp);
32 int BIO_set_info_callback(BIO *b,bio_info_cb *cb);
33
34 typedef void bio_info_cb(BIO *b, int oper, const char *ptr, int arg1, long arg2, long arg3);
35
36=head1 DESCRIPTION
37
38BIO_ctrl(), BIO_callback_ctrl(), BIO_ptr_ctrl() and BIO_int_ctrl()
39are BIO "control" operations taking arguments of various types.
40These functions are not normally called directly, various macros
41are used instead. The standard macros are described below, macros
42specific to a particular type of BIO are described in the specific
43BIOs manual page as well as any special features of the standard
44calls.
45
46BIO_reset() typically resets a BIO to some initial state, in the case
47of file related BIOs for example it rewinds the file pointer to the
48start of the file.
49
50BIO_seek() resets a file related BIO's (that is file descriptor and
51FILE BIOs) file position pointer to B<ofs> bytes from start of file.
52
53BIO_tell() returns the current file position of a file related BIO.
54
55BIO_flush() normally writes out any internally buffered data, in some
56cases it is used to signal EOF and that no more data will be written.
57
58BIO_eof() returns 1 if the BIO has read EOF, the precise meaning of
59"EOF" varies according to the BIO type.
60
61BIO_set_close() sets the BIO B<b> close flag to B<flag>. B<flag> can
62take the value BIO_CLOSE or BIO_NOCLOSE. Typically BIO_CLOSE is used
63in a source/sink BIO to indicate that the underlying I/O stream should
64be closed when the BIO is freed.
65
66BIO_get_close() returns the BIOs close flag.
67
68BIO_pending(), BIO_ctrl_pending(), BIO_wpending() and BIO_ctrl_wpending()
69return the number of pending characters in the BIOs read and write buffers.
70Not all BIOs support these calls. BIO_ctrl_pending() and BIO_ctrl_wpending()
71return a size_t type and are functions, BIO_pending() and BIO_wpending() are
72macros which call BIO_ctrl().
73
74=head1 RETURN VALUES
75
76BIO_reset() normally returns 1 for success and 0 or -1 for failure. File
77BIOs are an exception, they return 0 for success and -1 for failure.
78
79BIO_seek() and BIO_tell() both return the current file position on success
80and -1 for failure, except file BIOs which for BIO_seek() always return 0
81for success and -1 for failure.
82
83BIO_flush() returns 1 for success and 0 or -1 for failure.
84
85BIO_eof() returns 1 if EOF has been reached 0 otherwise.
86
87BIO_set_close() always returns 1.
88
89BIO_get_close() returns the close flag value: BIO_CLOSE or BIO_NOCLOSE.
90
91BIO_pending(), BIO_ctrl_pending(), BIO_wpending() and BIO_ctrl_wpending()
92return the amount of pending data.
93
94=head1 NOTES
95
96BIO_flush(), because it can write data may return 0 or -1 indicating
97that the call should be retried later in a similar manner to BIO_write(). 
98The BIO_should_retry() call should be used and appropriate action taken
99is the call fails.
100
101The return values of BIO_pending() and BIO_wpending() may not reliably
102determine the amount of pending data in all cases. For example in the
103case of a file BIO some data may be available in the FILE structures
104internal buffers but it is not possible to determine this in a
105portably way. For other types of BIO they may not be supported.
106
107Filter BIOs if they do not internally handle a particular BIO_ctrl()
108operation usually pass the operation to the next BIO in the chain.
109This often means there is no need to locate the required BIO for
110a particular operation, it can be called on a chain and it will
111be automatically passed to the relevant BIO. However this can cause
112unexpected results: for example no current filter BIOs implement
113BIO_seek(), but this may still succeed if the chain ends in a FILE
114or file descriptor BIO.
115
116Source/sink BIOs return an 0 if they do not recognize the BIO_ctrl()
117operation.
118
119=head1 BUGS
120
121Some of the return values are ambiguous and care should be taken. In
122particular a return value of 0 can be returned if an operation is not
123supported, if an error occurred, if EOF has not been reached and in
124the case of BIO_seek() on a file BIO for a successful operation. 
125
126=head1 SEE ALSO
127
128TBA
129