openssl/doc/man3/BIO_s_mem.pod

=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. 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 = 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 RETURN VALUES

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

BIO_set_mem_eof_return(), BIO_get_mem_data(), 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_new_mem_buf() returns a valid B<BIO> structure on success or NULL on error.

=head1 COPYRIGHT

Copyright 2000-2018 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>.

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