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✏️ Editing: BIO_s_mem.3

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.\" ========================================================================
.\"
.IX Title "BIO_S_MEM 3"
.TH BIO_S_MEM 3 "2023-09-11" "1.1.1w" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "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
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #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);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBBIO_s_mem()\fR returns the memory \s-1BIO\s0 method function.
.PP
A memory \s-1BIO\s0 is a source/sink \s-1BIO\s0 which uses memory for its I/O. Data
written to a memory \s-1BIO\s0 is stored in a \s-1BUF_MEM\s0 structure which is extended
as appropriate to accommodate the stored data.
.PP
\&\fBBIO_s_secmem()\fR is like \fBBIO_s_mem()\fR except that the secure heap is used
for buffer storage.
.PP
Any data written to a memory \s-1BIO\s0 can be recalled by reading from it.
Unless the memory \s-1BIO\s0 is read only any data read from it is deleted from
the \s-1BIO.\s0
.PP
Memory BIOs support \fBBIO_gets()\fR and \fBBIO_puts()\fR.
.PP
If the \s-1BIO_CLOSE\s0 flag is set when a memory \s-1BIO\s0 is freed then the underlying
\&\s-1BUF_MEM\s0 structure is also freed.
.PP
Calling \fBBIO_reset()\fR on a read write memory \s-1BIO\s0 clears any data in it if the
flag \s-1BIO_FLAGS_NONCLEAR_RST\s0 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 \s-1BIO\s0 it similarly restores the \s-1BIO\s0 to
its original state and the read only data can be read again.
.PP
\&\fBBIO_eof()\fR is true if no data is in the \s-1BIO.\s0
.PP
\&\fBBIO_ctrl_pending()\fR returns the number of bytes currently stored.
.PP
\&\fBBIO_set_mem_eof_return()\fR sets the behaviour of memory \s-1BIO\s0 \fBb\fR when it is
empty. If the \fBv\fR is zero then an empty memory \s-1BIO\s0 will return \s-1EOF\s0 (that is
it will return zero and BIO_should_retry(b) will be false. If \fBv\fR is non
zero then it will return \fBv\fR 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 \fBv\fR should be set to a negative value, typically \-1.
.PP
\&\fBBIO_get_mem_data()\fR sets *\fBpp\fR 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.
.PP
\&\fBBIO_set_mem_buf()\fR sets the internal \s-1BUF_MEM\s0 structure to \fBbm\fR and sets the
close flag to \fBc\fR, that is \fBc\fR should be either \s-1BIO_CLOSE\s0 or \s-1BIO_NOCLOSE.\s0
It is a macro.
.PP
\&\fBBIO_get_mem_ptr()\fR places the underlying \s-1BUF_MEM\s0 structure in *\fBpp\fR. It is
a macro.
.PP
\&\fBBIO_new_mem_buf()\fR creates a memory \s-1BIO\s0 using \fBlen\fR bytes of data at \fBbuf\fR,
if \fBlen\fR is \-1 then the \fBbuf\fR is assumed to be nul terminated and its
length is determined by \fBstrlen\fR. The \s-1BIO\s0 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 \s-1BIO.\s0 The
supplied data is read directly from the supplied buffer: it is \fBnot\fR copied
first, so the supplied area of memory must be unchanged until the \s-1BIO\s0 is freed.
.SH "NOTES"
.IX Header "NOTES"
Writes to memory BIOs will always succeed if memory is available: that is
their size can grow indefinitely.
.PP
Every write after partial read (not all data in the memory buffer was read)
to a read write memory \s-1BIO\s0 will have to move the unread data with an internal
copy operation, if a \s-1BIO\s0 contains a lot of data and it is read in small
chunks intertwined with writes the operation can be very slow. Adding
a buffering \s-1BIO\s0 to the chain can speed up the process.
.PP
Calling \fBBIO_set_mem_buf()\fR on a \s-1BIO\s0 created with \fBBIO_new_secmem()\fR will
give undefined results, including perhaps a program crash.
.PP
Switching the memory \s-1BIO\s0 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 \s-1BIO\s0 creation and set the \s-1BIO\s0 as read only.
.PP
The other supported sequence is to start with read write \s-1BIO\s0 then temporarily
switch it to read only and call \fBBIO_reset()\fR on the read only \s-1BIO\s0 immediately
before switching it back to read write. Before the \s-1BIO\s0 is freed it must be
switched back to the read write mode.
.PP
Calling \fBBIO_get_mem_ptr()\fR on read only \s-1BIO\s0 will return a \s-1BUF_MEM\s0 that
contains only the remaining data to be read. If the close status of the
\&\s-1BIO\s0 is set to \s-1BIO_NOCLOSE,\s0 before freeing the \s-1BUF_MEM\s0 the data pointer
in it must be set to \s-1NULL\s0 as the data pointer does not point to an
allocated memory.
.PP
Calling \fBBIO_reset()\fR on a read write memory \s-1BIO\s0 with \s-1BIO_FLAGS_NONCLEAR_RST\s0
flag set can have unexpected outcome when the reads and writes to the
\&\s-1BIO\s0 are intertwined. As documented above the \s-1BIO\s0 will be reset to the
state after the last completed write operation. The effects of reads
preceding that write operation cannot be undone.
.PP
Calling \fBBIO_get_mem_ptr()\fR prior to a \fBBIO_reset()\fR call with
\&\s-1BIO_FLAGS_NONCLEAR_RST\s0 set has the same effect as a write operation.
.SH "BUGS"
.IX Header "BUGS"
There should be an option to set the maximum size of a memory \s-1BIO.\s0
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBBIO_s_mem()\fR and \fBBIO_s_secmem()\fR return a valid memory \fB\s-1BIO_METHOD\s0\fR structure.
.PP
\&\fBBIO_set_mem_eof_return()\fR, \fBBIO_set_mem_buf()\fR and \fBBIO_get_mem_ptr()\fR
return 1 on success or a value which is less than or equal to 0 if an error occurred.
.PP
\&\fBBIO_get_mem_data()\fR returns the total number of bytes available on success,
0 if b is \s-1NULL,\s0 or a negative value in case of other errors.
.PP
\&\fBBIO_new_mem_buf()\fR returns a valid \fB\s-1BIO\s0\fR structure on success or \s-1NULL\s0 on error.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Create a memory \s-1BIO\s0 and write some data to it:
.PP
.Vb 1
\& BIO *mem = BIO_new(BIO_s_mem());
\&
\& BIO_puts(mem, "Hello World\en");
.Ve
.PP
Create a read only memory \s-1BIO:\s0
.PP
.Vb 2
\& char data[] = "Hello World";
\& BIO *mem = BIO_new_mem_buf(data, \-1);
.Ve
.PP
Extract the \s-1BUF_MEM\s0 structure from a memory \s-1BIO\s0 and then free up the \s-1BIO:\s0
.PP
.Vb 1
\& 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);
.Ve
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2000\-2019 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the OpenSSL license (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.

MR SKB