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);
long
BIO_set_mem_eof_return(BIO *b,
int v);
long
BIO_get_mem_data(BIO *b,
char **pp);
long
BIO_set_mem_buf(BIO *b,
BUF_MEM *bm, int c);
long
BIO_get_mem_ptr(BIO *b,
BUF_MEM **pp);
BIO *
BIO_new_mem_buf(void *buf,
int len);
DESCRIPTION
BIO_s_mem()
returns 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(3) and BIO_puts(3).
If the BIO_CLOSE flag is set when a memory
BIO is freed, the underlying BUF_MEM structure is
also freed.
Calling BIO_reset(3) 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(3) is true if no data is in the BIO.
BIO_ctrl_pending(3) returns the number of bytes currently stored.
BIO_set_mem_eof_return(3) sets the behaviour of memory BIO
b when it is empty. If v is
zero, then an empty memory BIO will return EOF: It will return zero and
BIO_should_retry()
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:
BIO_read_retry()
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 BIO's
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.
BIO_set_mem_buf() 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
buf is assumed to be NUL terminated and its length is
determined by strlen(3). 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 a lot 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.
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); /* Make sure BIO_free() leaves BUF_MEM alone. */ BIO_set_close(mem, BIO_NOCLOSE); BIO_free(mem);
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.