BIO_s_mem.pod revision 331638 
1=pod
2
3=head1 NAME
4
5BIO_s_mem, BIO_set_mem_eof_return, BIO_get_mem_data, BIO_set_mem_buf,
6BIO_get_mem_ptr, BIO_new_mem_buf - memory BIO
7
8=head1 SYNOPSIS
9
10 #include <openssl/bio.h>
11
12 BIO_METHOD *	BIO_s_mem(void);
13
14 BIO_set_mem_eof_return(BIO *b,int v)
15 long BIO_get_mem_data(BIO *b, char **pp)
16 BIO_set_mem_buf(BIO *b,BUF_MEM *bm,int c)
17 BIO_get_mem_ptr(BIO *b,BUF_MEM **pp)
18
19 BIO *BIO_new_mem_buf(const void *buf, int len);
20
21=head1 DESCRIPTION
22
23BIO_s_mem() return the memory BIO method function. 
24
25A memory BIO is a source/sink BIO which uses memory for its I/O. Data
26written to a memory BIO is stored in a BUF_MEM structure which is extended
27as appropriate to accommodate the stored data.
28
29Any data written to a memory BIO can be recalled by reading from it.
30Unless the memory BIO is read only any data read from it is deleted from
31the BIO.
32
33Memory BIOs support BIO_gets() and BIO_puts().
34
35If the BIO_CLOSE flag is set when a memory BIO is freed then the underlying
36BUF_MEM structure is also freed.
37
38Calling BIO_reset() on a read write memory BIO clears any data in it. On a
39read only BIO it restores the BIO to its original state and the read only
40data can be read again.
41
42BIO_eof() is true if no data is in the BIO.
43
44BIO_ctrl_pending() returns the number of bytes currently stored.
45
46BIO_set_mem_eof_return() sets the behaviour of memory BIO B<b> when it is
47empty. If the B<v> is zero then an empty memory BIO will return EOF (that is
48it will return zero and BIO_should_retry(b) will be false. If B<v> is non
49zero then it will return B<v> when it is empty and it will set the read retry
50flag (that is BIO_read_retry(b) is true). To avoid ambiguity with a normal
51positive return value B<v> should be set to a negative value, typically -1.
52
53BIO_get_mem_data() sets *B<pp> to a pointer to the start of the memory BIOs data
54and returns the total amount of data available. It is implemented as a macro.
55
56BIO_set_mem_buf() sets the internal BUF_MEM structure to B<bm> and sets the
57close flag to B<c>, that is B<c> should be either BIO_CLOSE or BIO_NOCLOSE.
58It is a macro.
59
60BIO_get_mem_ptr() places the underlying BUF_MEM structure in *B<pp>. It is
61a macro.
62
63BIO_new_mem_buf() creates a memory BIO using B<len> bytes of data at B<buf>,
64if B<len> is -1 then the B<buf> is assumed to be nul terminated and its
65length is determined by B<strlen>. The BIO is set to a read only state and
66as a result cannot be written to. This is useful when some data needs to be
67made available from a static area of memory in the form of a BIO. The
68supplied data is read directly from the supplied buffer: it is B<not> copied
69first, so the supplied area of memory must be unchanged until the BIO is freed.
70
71=head1 NOTES
72
73Writes to memory BIOs will always succeed if memory is available: that is
74their size can grow indefinitely.
75
76Every read from a read write memory BIO will remove the data just read with
77an internal copy operation, if a BIO contains a lot of data and it is
78read in small chunks the operation can be very slow. The use of a read only
79memory BIO avoids this problem. If the BIO must be read write then adding
80a buffering BIO to the chain will speed up the process.
81
82=head1 BUGS
83
84There should be an option to set the maximum size of a memory BIO.
85
86There should be a way to "rewind" a read write BIO without destroying
87its contents.
88
89The copying operation should not occur after every small read of a large BIO
90to improve efficiency.
91
92=head1 EXAMPLE
93
94Create a memory BIO and write some data to it:
95
96 BIO *mem = BIO_new(BIO_s_mem());
97 BIO_puts(mem, "Hello World\n"); 
98
99Create a read only memory BIO:
100
101 char data[] = "Hello World";
102 BIO *mem;
103 mem = BIO_new_mem_buf(data, -1);
104
105Extract the BUF_MEM structure from a memory BIO and then free up the BIO:
106
107 BUF_MEM *bptr;
108 BIO_get_mem_ptr(mem, &bptr);
109 BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free() leaves BUF_MEM alone */
110 BIO_free(mem);
111 
112
113=head1 SEE ALSO
114
115TBA
116