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
#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);
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
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. Note the pointer returned by this call is informative,
no transfer of ownership of this memory is implied. See notes on
BIO_set_close().
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 a macro.
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 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.
Calling
BIO_set_close() with BIO_NOCLOSE orphans the BUF_MEM internal to
the BIO, _not_ its actual data buffer. See the examples section for the proper
method for claiming ownership of the data pointer for a deferred free
operation.
There should be an option to set the maximum size of a memory BIO.
BIO_s_mem() and
BIO_s_secmem() return a valid memory
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
BIO structure on success or NULL
on error.
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);
Extract the BUF_MEM ptr, claim ownership of the internal data and free the BIO
and BUF_MEM structure:
BUF_MEM *bptr;
char *data;
BIO_get_mem_data(bio, &data);
BIO_get_mem_ptr(bio, &bptr);
BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free orphans BUF_MEM */
BIO_free(bio);
bptr->data = NULL; /* Tell BUF_MEM to orphan data */
BUF_MEM_free(bptr);
...
free(data);
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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
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