doc/man3/BIO_s_mem.pod - third_party/openssl - Git at Google

 =pod

 =head1 NAME

 BIO_s_secmem,
 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() 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.

 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, otherwise it just restores the read
 pointer to the state it was just after the last write was performed and the
 data can be read again. On a read only BIO it similarly 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<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 write after partial read (not all data in the memory buffer was read)
 to a read write memory BIO will have to move the unread data with an internal
 copy operation, if a BIO contains a lot of data and it is read in small
 chunks intertwined with writes the operation can be very slow. Adding
 a buffering BIO to the chain can 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.

 Switching the memory BIO from read write to read only is not supported and
 can give undefined results including a program crash. There are two notable
 exceptions to the rule. The first one is to assign a static memory buffer
 immediately after BIO creation and set the BIO as read only.

 The other supported sequence is to start with read write BIO then temporarily
 switch it to read only and call BIO_reset() on the read only BIO immediately
 before switching it back to read write. Before the BIO is freed it must be
 switched back to the read write mode.

 Calling BIO_get_mem_ptr() on read only BIO will return a BUF_MEM that
 contains only the remaining data to be read. If the close status of the
 BIO is set to BIO_NOCLOSE, before freeing the BUF_MEM the data pointer
 in it must be set to NULL as the data pointer does not point to an
 allocated memory.

 Calling BIO_reset() on a read write memory BIO with BIO_FLAGS_NONCLEAR_RST
 flag set can have unexpected outcome when the reads and writes to the
 BIO are intertwined. As documented above the BIO will be reset to the
 state after the last completed write operation. The effects of reads
 preceding that write operation cannot be undone.

 Calling BIO_get_mem_ptr() prior to a BIO_reset() call with
 BIO_FLAGS_NONCLEAR_RST set has the same effect as a write operation.

 =head1 BUGS

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

 =head1 RETURN VALUES

 BIO_s_mem() and BIO_s_secmem() return a valid memory B<BIO_METHOD> structure.

 BIO_set_mem_eof_return(), BIO_set_mem_buf() and BIO_get_mem_ptr()
 return 1 on success or a value which is less than or equal to 0 if an error occurred.

 BIO_get_mem_data() returns the total number of bytes available on success,
 0 if b is NULL, or a negative value in case of other errors.

 BIO_new_mem_buf() returns a valid B<BIO> structure on success or NULL on error.

 =head1 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 = 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 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

 Licensed under the Apache License 2.0 (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
	=pod

	=head1 NAME

	BIO_s_secmem,
	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() 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.

	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, otherwise it just restores the read
	pointer to the state it was just after the last write was performed and the
	data can be read again. On a read only BIO it similarly 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<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 write after partial read (not all data in the memory buffer was read)
	to a read write memory BIO will have to move the unread data with an internal
	copy operation, if a BIO contains a lot of data and it is read in small
	chunks intertwined with writes the operation can be very slow. Adding
	a buffering BIO to the chain can 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.

	Switching the memory BIO from read write to read only is not supported and
	can give undefined results including a program crash. There are two notable
	exceptions to the rule. The first one is to assign a static memory buffer
	immediately after BIO creation and set the BIO as read only.

	The other supported sequence is to start with read write BIO then temporarily
	switch it to read only and call BIO_reset() on the read only BIO immediately
	before switching it back to read write. Before the BIO is freed it must be
	switched back to the read write mode.

	Calling BIO_get_mem_ptr() on read only BIO will return a BUF_MEM that
	contains only the remaining data to be read. If the close status of the
	BIO is set to BIO_NOCLOSE, before freeing the BUF_MEM the data pointer
	in it must be set to NULL as the data pointer does not point to an
	allocated memory.

	Calling BIO_reset() on a read write memory BIO with BIO_FLAGS_NONCLEAR_RST
	flag set can have unexpected outcome when the reads and writes to the
	BIO are intertwined. As documented above the BIO will be reset to the
	state after the last completed write operation. The effects of reads
	preceding that write operation cannot be undone.

	Calling BIO_get_mem_ptr() prior to a BIO_reset() call with
	BIO_FLAGS_NONCLEAR_RST set has the same effect as a write operation.

	=head1 BUGS

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

	=head1 RETURN VALUES

	BIO_s_mem() and BIO_s_secmem() return a valid memory B<BIO_METHOD> structure.

	BIO_set_mem_eof_return(), BIO_set_mem_buf() and BIO_get_mem_ptr()
	return 1 on success or a value which is less than or equal to 0 if an error occurred.

	BIO_get_mem_data() returns the total number of bytes available on success,
	0 if b is NULL, or a negative value in case of other errors.

	BIO_new_mem_buf() returns a valid B<BIO> structure on success or NULL on error.

	=head1 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 = 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 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

	Licensed under the Apache License 2.0 (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