1=pod
2
3=head1 NAME
4
5BIO_s_secmem,
6BIO_s_mem, BIO_set_mem_eof_return, BIO_get_mem_data, BIO_set_mem_buf,
7BIO_get_mem_ptr, BIO_new_mem_buf - memory BIO
8
9=head1 SYNOPSIS
10
11 #include <openssl/bio.h>
12
13 const BIO_METHOD *BIO_s_mem(void);
14 const BIO_METHOD *BIO_s_secmem(void);
15
16 BIO_set_mem_eof_return(BIO *b, int v);
17 long BIO_get_mem_data(BIO *b, char **pp);
18 BIO_set_mem_buf(BIO *b, BUF_MEM *bm, int c);
19 BIO_get_mem_ptr(BIO *b, BUF_MEM **pp);
20
21 BIO *BIO_new_mem_buf(const void *buf, int len);
22
23=head1 DESCRIPTION
24
25BIO_s_mem() returns the memory BIO method function.
26
27A memory BIO is a source/sink BIO which uses memory for its I/O. Data
28written to a memory BIO is stored in a BUF_MEM structure which is extended
29as appropriate to accommodate the stored data.
30
31BIO_s_secmem() is like BIO_s_mem() except that the secure heap is used
32for buffer storage.
33
34Any data written to a memory BIO can be recalled by reading from it.
35Unless the memory BIO is read only any data read from it is deleted from
36the BIO.
37
38Memory BIOs support BIO_gets() and BIO_puts().
39
40If the BIO_CLOSE flag is set when a memory BIO is freed then the underlying
41BUF_MEM structure is also freed.
42
43Calling BIO_reset() on a read write memory BIO clears any data in it if the
44flag BIO_FLAGS_NONCLEAR_RST is not set, otherwise it just restores the read
45pointer to the state it was just after the last write was performed and the
46data can be read again. On a read only BIO it similarly restores the BIO to
47its original state and the read only data can be read again.
48
49BIO_eof() is true if no data is in the BIO.
50
51BIO_ctrl_pending() returns the number of bytes currently stored.
52
53BIO_set_mem_eof_return() sets the behaviour of memory BIO B<b> when it is
54empty. If the B<v> is zero then an empty memory BIO will return EOF (that is
55it will return zero and BIO_should_retry(b) will be false. If B<v> is non
56zero then it will return B<v> when it is empty and it will set the read retry
57flag (that is BIO_read_retry(b) is true). To avoid ambiguity with a normal
58positive return value B<v> should be set to a negative value, typically -1.
59
60BIO_get_mem_data() sets *B<pp> to a pointer to the start of the memory BIOs data
61and returns the total amount of data available. It is implemented as a macro.
62
63BIO_set_mem_buf() sets the internal BUF_MEM structure to B<bm> and sets the
64close flag to B<c>, that is B<c> should be either BIO_CLOSE or BIO_NOCLOSE.
65It is a macro.
66
67BIO_get_mem_ptr() places the underlying BUF_MEM structure in *B<pp>. It is
68a macro.
69
70BIO_new_mem_buf() creates a memory BIO using B<len> bytes of data at B<buf>,
71if B<len> is -1 then the B<buf> is assumed to be nul terminated and its
72length is determined by B<strlen>. The BIO is set to a read only state and
73as a result cannot be written to. This is useful when some data needs to be
74made available from a static area of memory in the form of a BIO. The
75supplied data is read directly from the supplied buffer: it is B<not> copied
76first, so the supplied area of memory must be unchanged until the BIO is freed.
77
78=head1 NOTES
79
80Writes to memory BIOs will always succeed if memory is available: that is
81their size can grow indefinitely.
82
83Every write after partial read (not all data in the memory buffer was read)
84to a read write memory BIO will have to move the unread data with an internal
85copy operation, if a BIO contains a lot of data and it is read in small
86chunks intertwined with writes the operation can be very slow. Adding
87a buffering BIO to the chain can speed up the process.
88
89Calling BIO_set_mem_buf() on a BIO created with BIO_new_secmem() will
90give undefined results, including perhaps a program crash.
91
92Switching the memory BIO from read write to read only is not supported and
93can give undefined results including a program crash. There are two notable
94exceptions to the rule. The first one is to assign a static memory buffer
95immediately after BIO creation and set the BIO as read only.
96
97The other supported sequence is to start with read write BIO then temporarily
98switch it to read only and call BIO_reset() on the read only BIO immediately
99before switching it back to read write. Before the BIO is freed it must be
100switched back to the read write mode.
101
102Calling BIO_get_mem_ptr() on read only BIO will return a BUF_MEM that
103contains only the remaining data to be read. If the close status of the
104BIO is set to BIO_NOCLOSE, before freeing the BUF_MEM the data pointer
105in it must be set to NULL as the data pointer does not point to an
106allocated memory.
107
108Calling BIO_reset() on a read write memory BIO with BIO_FLAGS_NONCLEAR_RST
109flag set can have unexpected outcome when the reads and writes to the
110BIO are intertwined. As documented above the BIO will be reset to the
111state after the last completed write operation. The effects of reads
112preceding that write operation cannot be undone.
113
114Calling BIO_get_mem_ptr() prior to a BIO_reset() call with
115BIO_FLAGS_NONCLEAR_RST set has the same effect as a write operation.
116
117=head1 BUGS
118
119There should be an option to set the maximum size of a memory BIO.
120
121=head1 RETURN VALUES
122
123BIO_s_mem() and BIO_s_secmem() return a valid memory B<BIO_METHOD> structure.
124
125BIO_set_mem_eof_return(), BIO_set_mem_buf() and BIO_get_mem_ptr()
126return 1 on success or a value which is less than or equal to 0 if an error occurred.
127
128BIO_get_mem_data() returns the total number of bytes available on success,
1290 if b is NULL, or a negative value in case of other errors.
130
131BIO_new_mem_buf() returns a valid B<BIO> structure on success or NULL on error.
132
133=head1 EXAMPLES
134
135Create a memory BIO and write some data to it:
136
137 BIO *mem = BIO_new(BIO_s_mem());
138
139 BIO_puts(mem, "Hello World\n");
140
141Create a read only memory BIO:
142
143 char data[] = "Hello World";
144 BIO *mem = BIO_new_mem_buf(data, -1);
145
146Extract the BUF_MEM structure from a memory BIO and then free up the BIO:
147
148 BUF_MEM *bptr;
149
150 BIO_get_mem_ptr(mem, &bptr);
151 BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free() leaves BUF_MEM alone */
152 BIO_free(mem);
153
154
155=head1 COPYRIGHT
156
157Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
158
159Licensed under the Apache License 2.0 (the "License").  You may not use
160this file except in compliance with the License.  You can obtain a copy
161in the file LICENSE in the source distribution or at
162L<https://www.openssl.org/source/license.html>.
163
164=cut
165