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_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)
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
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. 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 much 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
There should be an option to set the maximum size of a
There should be a way to rewind a read-write BIO without
destroying its contents.
To improve efficiency, the copying operation should not
occur after every small read of a large BIO.
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);
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