1BIO_s_mem(3)                        OpenSSL                       BIO_s_mem(3)
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NAME

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

10        #include <openssl/bio.h>
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12        BIO_METHOD *   BIO_s_mem(void);
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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)
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19        BIO *BIO_new_mem_buf(const void *buf, int len);
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DESCRIPTION

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

74       Writes to memory BIOs will always succeed if memory is available: that
75       is their size can grow indefinitely.
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77       Every read from a read write memory BIO will remove the data just read
78       with an internal copy operation, if a BIO contains a lot of data and it
79       is read in small chunks the operation can be very slow. The use of a
80       read only memory BIO avoids this problem. If the BIO must be read write
81       then adding a buffering BIO to the chain will speed up the process.
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BUGS

84       There should be an option to set the maximum size of a memory BIO.
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86       There should be a way to "rewind" a read write BIO without destroying
87       its contents.
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89       The copying operation should not occur after every small read of a
90       large BIO to improve efficiency.
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EXAMPLE

93       Create a memory BIO and write some data to it:
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95        BIO *mem = BIO_new(BIO_s_mem());
96        BIO_puts(mem, "Hello World\n");
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98       Create a read only memory BIO:
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100        char data[] = "Hello World";
101        BIO *mem;
102        mem = BIO_new_mem_buf(data, -1);
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104       Extract the BUF_MEM structure from a memory BIO and then free up the
105       BIO:
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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);
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SEE ALSO

113       TBA
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1171.0.2o                            2019-09-10                      BIO_s_mem(3)
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