BIO_s_mem(3) OpenSSL BIO_s_mem(3)NAME
BIO_s_mem, BIO_set_mem_eof_return, BIO_get_mem_data,
BIO_set_mem_buf, BIO_get_mem_ptr, BIO_new_mem_buf - memory
BIO
SYNOPSIS
#include <openssl/bio.h>
BIO_METHOD * BIO_s_mem(void);
BIO_set_mem_eof_return(BIO *b,int v)
long BIO_get_mem_data(BIO *b, char **pp)
BIO_set_mem_buf(BIO *b,BUF_MEM *bm,int c)
BIO_get_mem_ptr(BIO *b,BUF_MEM **pp)
BIO *BIO_new_mem_buf(void *buf, int len);
DESCRIPTIONBIO_s_mem() return the memory BIO method function.
A memory BIO is a source/sink BIO which uses memory for
its I/O. Data written to a memory BIO is stored in a
BUF_MEM structure which is extended as appropriate to
accommodate the stored data.
Any data written to a memory BIO can be recalled by
reading from it. Unless the memory BIO is read only any
data read from it is deleted from the BIO.
Memory BIOs support BIO_gets() and BIO_puts().
If the BIO_CLOSE flag is set when a memory BIO is freed
then the underlying BUF_MEM structure is also freed.
Calling BIO_reset() on a read write memory BIO clears any
data in it. On a read only BIO it restores the BIO to its
original state and the read only data can be read again.
BIO_eof() is true if no data is in the BIO.
BIO_ctrl_pending() returns the number of bytes currently
stored.
BIO_set_mem_eof_return() sets the behaviour of memory BIO
b when it is empty. If the v is zero then an empty memory
BIO will return EOF (that is it will return zero and
BIO_should_retry(b) will be false. If v is non zero then
it will return v when it is empty and it will set the read
retry flag (that is BIO_read_retry(b) is true). To avoid
ambiguity with a normal positive return value v should be
set to a negative value, typically -1.
BIO_get_mem_data() sets pp to a pointer to the start of
the memory BIOs data and returns the total amount of data
available. It is implemented as a macro.
BIO_set_mem_buf() sets the internal BUF_MEM structure to
bm and sets the close flag to c, that is c should be
either BIO_CLOSE or BIO_NOCLOSE. It is a macro.
BIO_get_mem_ptr() places the underlying BUF_MEM structure
in pp. It is a macro.
BIO_new_mem_buf() creates a memory BIO using len bytes of
data at buf, if len is -1 then the buf is assumed to be
null terminated and its length is determined by strlen.
The BIO is set to a read only state and as a result cannot
be written to. This is useful when some data needs to be
made available from a static area of memory in the form of
a BIO. The supplied data is read directly from the
supplied buffer: it is not copied first, so the supplied
area of memory must be unchanged until the BIO is freed.
NOTES
Writes to memory BIOs will always succeed if memory is
available: that is their size can grow indefinitely.
Every read from a read write memory BIO will remove the
data just read with an internal copy operation, if a BIO
contains a lots of data and it is read in small chunks the
operation can be very slow. The use of a read only memory
BIO avoids this problem. If the BIO must be read write
then adding a buffering BIO to the chain will speed up the
process.
BUGS
There should be an option to set the maximum size of a
memory BIO.
There should be a way to "rewind" a read write BIO without
destroying its contents.
The copying operation should not occur after every small
read of a large BIO to improve efficiency.
EXAMPLE
Create a memory BIO and write some data to it:
BIO *mem = BIO_new(BIO_s_mem());
BIO_puts(mem, "Hello World\n");
Create a read only memory BIO:
char data[] = "Hello World";
BIO *mem;
mem = BIO_new_mem_buf(data, -1);
Extract the BUF_MEM structure from a memory BIO and then
free up the BIO:
BUF_MEM *bptr;
BIO_get_mem_ptr(mem, &bptr);
BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free() leaves BUF_MEM alone */
BIO_free(mem);
SEE ALSO
TBA
16/Sep/2000 0.9.6j BIO_s_mem(3)
