[thirdparty/openssl.git] / doc / crypto / BIO_s_mem.pod

=pod

=head1 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

=head1 SYNOPSIS

 #include <openssl/bio.h>

 const BIO_METHOD *     BIO_s_mem(void);
 const BIO_METHOD *     BIO_s_secmem(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);

=head1 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.

BIO_s_secmem() is like BIO_s_mem() except that the secure heap is used
for buffer storage.

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 if the
flag BIO_FLAGS_NONCLEAR_RST is not set. On a read only BIO or if the flag
BIO_FLAGS_NONCLEAR_RST is set it restores the BIO to its original state and
the 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<b> when it is
empty. If the B<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 B<v> is non
zero then it will return B<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 B<v> should be set to a negative value, typically -1.

BIO_get_mem_data() sets B<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 B<bm> and sets the
close flag to B<c>, that is B<c> should be either BIO_CLOSE or BIO_NOCLOSE.
It is a macro.

BIO_get_mem_ptr() places the underlying BUF_MEM structure in B<pp>. It is
a macro.

BIO_new_mem_buf() creates a memory BIO using B<len> bytes of data at B<buf>,
if B<len> is -1 then the B<buf> is assumed to be nul terminated and its
length is determined by B<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 B<not> copied
first, so the supplied area of memory must be unchanged until the BIO is freed.

=head1 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 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.

Calling BIO_set_mem_buf() on a BIO created with BIO_new_secmem() will
give undefined results, including perhaps a program crash.

=head1 BUGS

There should be an option to set the maximum size of a memory BIO.

=head1 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);

=head1 COPYRIGHT

Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

=cut
Commit	Line	Data
d7b9c76c DSH	1	=pod
	2
	3	=head1 NAME
	4
8eec1389 RL	5	BIO_s_mem, BIO_set_mem_eof_return, BIO_get_mem_data, BIO_set_mem_buf,
8eec1389 RL	6	BIO_get_mem_ptr, BIO_new_mem_buf - memory BIO
d7b9c76c DSH	7
	8	=head1 SYNOPSIS
	9
	10	#include <openssl/bio.h>
	11
1bc74519 RS	12	const BIO_METHOD * BIO_s_mem(void);
1bc74519 RS	13	const BIO_METHOD * BIO_s_secmem(void);
d7b9c76c DSH	14
	15	BIO_set_mem_eof_return(BIO *b,int v)
	16	long BIO_get_mem_data(BIO b, char *pp)
	17	BIO_set_mem_buf(BIO b,BUF_MEM bm,int c)
	18	BIO_get_mem_ptr(BIO b,BUF_MEM *pp)
	19
8ab31975	20	BIO BIO_new_mem_buf(const void buf, int len);
d7b9c76c DSH	21
	22	=head1 DESCRIPTION
	23
1bc74519	24	BIO_s_mem() return the memory BIO method function.
d7b9c76c DSH	25
	26	A memory BIO is a source/sink BIO which uses memory for its I/O. Data
	27	written to a memory BIO is stored in a BUF_MEM structure which is extended
	28	as appropriate to accommodate the stored data.
	29
74924dcb RS	30	BIO_s_secmem() is like BIO_s_mem() except that the secure heap is used
	31	for buffer storage.
	32
d7b9c76c DSH	33	Any data written to a memory BIO can be recalled by reading from it.
	34	Unless the memory BIO is read only any data read from it is deleted from
	35	the BIO.
	36
	37	Memory BIOs support BIO_gets() and BIO_puts().
	38
	39	If the BIO_CLOSE flag is set when a memory BIO is freed then the underlying
	40	BUF_MEM structure is also freed.
	41
9fe9d046 KM	42	Calling BIO_reset() on a read write memory BIO clears any data in it if the
9fe9d046 KM	43	flag BIO_FLAGS_NONCLEAR_RST is not set. On a read only BIO or if the flag
1bc74519	44	BIO_FLAGS_NONCLEAR_RST is set it restores the BIO to its original state and
9fe9d046	45	the data can be read again.
d7b9c76c DSH	46
	47	BIO_eof() is true if no data is in the BIO.
	48
	49	BIO_ctrl_pending() returns the number of bytes currently stored.
	50
acb5b343	51	BIO_set_mem_eof_return() sets the behaviour of memory BIO B<b> when it is
d7b9c76c DSH	52	empty. If the B<v> is zero then an empty memory BIO will return EOF (that is
	53	it will return zero and BIO_should_retry(b) will be false. If B<v> is non
	54	zero then it will return B<v> when it is empty and it will set the read retry
	55	flag (that is BIO_read_retry(b) is true). To avoid ambiguity with a normal
	56	positive return value B<v> should be set to a negative value, typically -1.
	57
	58	BIO_get_mem_data() sets B<pp> to a pointer to the start of the memory BIOs data
	59	and returns the total amount of data available. It is implemented as a macro.
	60
	61	BIO_set_mem_buf() sets the internal BUF_MEM structure to B<bm> and sets the
	62	close flag to B<c>, that is B<c> should be either BIO_CLOSE or BIO_NOCLOSE.
	63	It is a macro.
	64
	65	BIO_get_mem_ptr() places the underlying BUF_MEM structure in B<pp>. It is
	66	a macro.
	67
	68	BIO_new_mem_buf() creates a memory BIO using B<len> bytes of data at B<buf>,
8ab31975	69	if B<len> is -1 then the B<buf> is assumed to be nul terminated and its
d7b9c76c DSH	70	length is determined by B<strlen>. The BIO is set to a read only state and
	71	as a result cannot be written to. This is useful when some data needs to be
	72	made available from a static area of memory in the form of a BIO. The
	73	supplied data is read directly from the supplied buffer: it is B<not> copied
	74	first, so the supplied area of memory must be unchanged until the BIO is freed.
	75
	76	=head1 NOTES
	77
	78	Writes to memory BIOs will always succeed if memory is available: that is
	79	their size can grow indefinitely.
	80
	81	Every read from a read write memory BIO will remove the data just read with
8711efb4	82	an internal copy operation, if a BIO contains a lot of data and it is
d7b9c76c DSH	83	read in small chunks the operation can be very slow. The use of a read only
	84	memory BIO avoids this problem. If the BIO must be read write then adding
	85	a buffering BIO to the chain will speed up the process.
	86
74924dcb RS	87	Calling BIO_set_mem_buf() on a BIO created with BIO_new_secmem() will
	88	give undefined results, including perhaps a program crash.
	89
d7b9c76c DSH	90	=head1 BUGS
	91
	92	There should be an option to set the maximum size of a memory BIO.
	93
d7b9c76c DSH	94	=head1 EXAMPLE
	95
	96	Create a memory BIO and write some data to it:
	97
	98	BIO *mem = BIO_new(BIO_s_mem());
1bc74519	99	BIO_puts(mem, "Hello World\n");
d7b9c76c DSH	100
	101	Create a read only memory BIO:
	102
	103	char data[] = "Hello World";
	104	BIO *mem;
	105	mem = BIO_new_mem_buf(data, -1);
	106
	107	Extract the BUF_MEM structure from a memory BIO and then free up the BIO:
	108
	109	BUF_MEM *bptr;
	110	BIO_get_mem_ptr(mem, &bptr);
	111	BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free() leaves BUF_MEM alone */
	112	BIO_free(mem);
1bc74519	113
e2f92610 RS	114	=head1 COPYRIGHT
	115
	116	Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
	117
	118	Licensed under the OpenSSL license (the "License"). You may not use
	119	this file except in compliance with the License. You can obtain a copy
	120	in the file LICENSE in the source distribution or at
	121	L<https://www.openssl.org/source/license.html>.
	122
	123	=cut