DragonFly On-Line Manual Pages
BIO(3) DragonFly Library Functions Manual BIO(3)
BIO -- I/O abstraction
A BIO is an I/O abstraction, it hides many of the underlying I/O details
from an application. If an application uses a BIO for its I/O, it can
transparently handle SSL connections, unencrypted network connections and
There are two types of BIO, a source/sink BIO and a filter BIO.
As its name implies, a source/sink BIO is a source and/or sink of data,
examples include a socket BIO and a file BIO.
A filter BIO takes data from one BIO and passes it through to another, or
to the application. The data may be left unmodified (for example a mes-
sage digest BIO) or translated (for example an encryption BIO). The
effect of a filter BIO may change according to the I/O operation it is
performing: for example an encryption BIO will encrypt data if it is
being written to and decrypt data if it is being read from.
BIOs can be joined together to form a chain (a single BIO is a chain with
one component). A chain normally consist of one source/sink BIO and one
or more filter BIOs. Data read from or written to the first BIO then
traverses the chain to the end (normally a source/sink BIO).
BIO_ctrl(3), BIO_f_base64(3), BIO_f_buffer(3), BIO_f_cipher(3),
BIO_f_md(3), BIO_f_null(3), BIO_f_ssl(3), BIO_find_type(3), BIO_new(3),
BIO_new_bio_pair(3), BIO_push(3), BIO_read(3), BIO_s_accept(3),
BIO_s_bio(3), BIO_s_connect(3), BIO_s_fd(3), BIO_s_file(3), BIO_s_mem(3),
BIO_s_null(3), BIO_s_socket(3), BIO_set_callback(3), BIO_should_retry(3)
DragonFly 4.7 July 17, 2014 DragonFly 4.7
BIO_s_mem(3) OpenSSL BIO_s_mem(3)
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_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(const 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
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 nul 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 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.
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
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_set_close(mem, BIO_NOCLOSE); /* So BIO_free() leaves BUF_MEM alone */
1.0.2h 2016-05-03 BIO_s_mem(3)