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
BIO_set_mem_eof_return(BIO *b,int v)
BIO_get_mem_data(BIO *b, char **pp)
*b,BUF_MEM *bm,int c)
BIO_get_mem_ptr(BIO *b,BUF_MEM **pp)
*BIO_new_mem_buf(void *buf, int len);
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 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.
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.
There should be an option to set the maximum size of a memory
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.
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 */