BIO_s_mem(3)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 under‐
lying 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. 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
process.
RESTRICTIONS
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.
To improve efficiency, the copying operation should not occur after
every small read of a large BIO.
EXAMPLES
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
BIO_s_mem(3)