1BIO_S_MEM(3)                        OpenSSL                       BIO_S_MEM(3)
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NAME

6       BIO_s_secmem, BIO_s_mem, BIO_set_mem_eof_return, BIO_get_mem_data,
7       BIO_set_mem_buf, BIO_get_mem_ptr, BIO_new_mem_buf - memory BIO
8

SYNOPSIS

10        #include <openssl/bio.h>
11
12        const BIO_METHOD *BIO_s_mem(void);
13        const BIO_METHOD *BIO_s_secmem(void);
14
15        BIO_set_mem_eof_return(BIO *b, int v)
16        long BIO_get_mem_data(BIO *b, char **pp)
17        BIO_set_mem_buf(BIO *b, BUF_MEM *bm, int c)
18        BIO_get_mem_ptr(BIO *b, BUF_MEM **pp)
19
20        BIO *BIO_new_mem_buf(const void *buf, int len);
21

DESCRIPTION

23       BIO_s_mem() returns the memory BIO method function.
24
25       A memory BIO is a source/sink BIO which uses memory for its I/O. Data
26       written to a memory BIO is stored in a BUF_MEM structure which is
27       extended as appropriate to accommodate the stored data.
28
29       BIO_s_secmem() is like BIO_s_mem() except that the secure heap is used
30       for buffer storage.
31
32       Any data written to a memory BIO can be recalled by reading from it.
33       Unless the memory BIO is read only any data read from it is deleted
34       from the BIO.
35
36       Memory BIOs support BIO_gets() and BIO_puts().
37
38       If the BIO_CLOSE flag is set when a memory BIO is freed then the
39       underlying BUF_MEM structure is also freed.
40
41       Calling BIO_reset() on a read write memory BIO clears any data in it if
42       the flag BIO_FLAGS_NONCLEAR_RST is not set, otherwise it just restores
43       the read pointer to the state it was just after the last write was
44       performed and the data can be read again. On a read only BIO it
45       similarly restores the BIO to its original state and the read only data
46       can be read again.
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48       BIO_eof() is true if no data is in the BIO.
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50       BIO_ctrl_pending() returns the number of bytes currently stored.
51
52       BIO_set_mem_eof_return() sets the behaviour of memory BIO b when it is
53       empty. If the v is zero then an empty memory BIO will return EOF (that
54       is it will return zero and BIO_should_retry(b) will be false. If v is
55       non zero then it will return v when it is empty and it will set the
56       read retry flag (that is BIO_read_retry(b) is true). To avoid ambiguity
57       with a normal positive return value v should be set to a negative
58       value, typically -1.
59
60       BIO_get_mem_data() sets *pp to a pointer to the start of the memory
61       BIOs data and returns the total amount of data available. It is
62       implemented as a macro.
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64       BIO_set_mem_buf() sets the internal BUF_MEM structure to bm and sets
65       the close flag to c, that is c should be either BIO_CLOSE or
66       BIO_NOCLOSE.  It is a macro.
67
68       BIO_get_mem_ptr() places the underlying BUF_MEM structure in *pp. It is
69       a macro.
70
71       BIO_new_mem_buf() creates a memory BIO using len bytes of data at buf,
72       if len is -1 then the buf is assumed to be nul terminated and its
73       length is determined by strlen. The BIO is set to a read only state and
74       as a result cannot be written to. This is useful when some data needs
75       to be made available from a static area of memory in the form of a BIO.
76       The supplied data is read directly from the supplied buffer: it is not
77       copied first, so the supplied area of memory must be unchanged until
78       the BIO is freed.
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NOTES

81       Writes to memory BIOs will always succeed if memory is available: that
82       is their size can grow indefinitely.
83
84       Every write after partial read (not all data in the memory buffer was
85       read) to a read write memory BIO will have to move the unread data with
86       an internal copy operation, if a BIO contains a lot of data and it is
87       read in small chunks intertwined with writes the operation can be very
88       slow. Adding a buffering BIO to the chain can speed up the process.
89
90       Calling BIO_set_mem_buf() on a BIO created with BIO_new_secmem() will
91       give undefined results, including perhaps a program crash.
92
93       Switching the memory BIO from read write to read only is not supported
94       and can give undefined results including a program crash. There are two
95       notable exceptions to the rule. The first one is to assign a static
96       memory buffer immediately after BIO creation and set the BIO as read
97       only.
98
99       The other supported sequence is to start with read write BIO then
100       temporarily switch it to read only and call BIO_reset() on the read
101       only BIO immediately before switching it back to read write. Before the
102       BIO is freed it must be switched back to the read write mode.
103
104       Calling BIO_get_mem_ptr() on read only BIO will return a BUF_MEM that
105       contains only the remaining data to be read. If the close status of the
106       BIO is set to BIO_NOCLOSE, before freeing the BUF_MEM the data pointer
107       in it must be set to NULL as the data pointer does not point to an
108       allocated memory.
109
110       Calling BIO_reset() on a read write memory BIO with
111       BIO_FLAGS_NONCLEAR_RST flag set can have unexpected outcome when the
112       reads and writes to the BIO are intertwined. As documented above the
113       BIO will be reset to the state after the last completed write
114       operation. The effects of reads preceding that write operation cannot
115       be undone.
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117       Calling BIO_get_mem_ptr() prior to a BIO_reset() call with
118       BIO_FLAGS_NONCLEAR_RST set has the same effect as a write operation.
119

BUGS

121       There should be an option to set the maximum size of a memory BIO.
122

RETURN VALUES

124       BIO_s_mem() and BIO_s_secmem() return a valid memory BIO_METHOD
125       structure.
126
127       BIO_set_mem_eof_return(), BIO_set_mem_buf() and BIO_get_mem_ptr()
128       return 1 on success or a value which is less than or equal to 0 if an
129       error occurred.
130
131       BIO_get_mem_data() returns the total number of bytes available on
132       success, 0 if b is NULL, or a negative value in case of other errors.
133
134       BIO_new_mem_buf() returns a valid BIO structure on success or NULL on
135       error.
136

EXAMPLES

138       Create a memory BIO and write some data to it:
139
140        BIO *mem = BIO_new(BIO_s_mem());
141
142        BIO_puts(mem, "Hello World\n");
143
144       Create a read only memory BIO:
145
146        char data[] = "Hello World";
147        BIO *mem = BIO_new_mem_buf(data, -1);
148
149       Extract the BUF_MEM structure from a memory BIO and then free up the
150       BIO:
151
152        BUF_MEM *bptr;
153
154        BIO_get_mem_ptr(mem, &bptr);
155        BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free() leaves BUF_MEM alone */
156        BIO_free(mem);
157
159       Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
160
161       Licensed under the OpenSSL license (the "License").  You may not use
162       this file except in compliance with the License.  You can obtain a copy
163       in the file LICENSE in the source distribution or at
164       <https://www.openssl.org/source/license.html>.
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1681.1.1q                            2023-02-06                      BIO_S_MEM(3)
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