=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 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 2000-2019 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>.

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