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);
DESCRIPTION
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.
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
0.9.7l 2000-09-16 BIO_s_mem(3)
|