BIO_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
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
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.
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";
mem = BIO_new_mem_buf(data, -1);
Extract the BUF_MEM structure from a memory BIO and then free up the BIO:
BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free() leaves BUF_MEM alone */