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.\" ========================================================================
.\"
.IX Title "BIO_s_mem 3"
.TH BIO_s_mem 3 "2019-12-20" "1.0.2u" "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_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>
\&
\& BIO_METHOD *   BIO_s_mem(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 return 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
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. On a
read only \s-1BIO\s0 it 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 read from a read write memory \s-1BIO\s0 will remove the data just read with
an internal copy operation, if a \s-1BIO\s0 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 \s-1BIO\s0 avoids this problem. If the \s-1BIO\s0 must be read write then adding
a buffering \s-1BIO\s0 to the chain will speed up the process.
.SH "BUGS"
.IX Header "BUGS"
There should be an option to set the maximum size of a memory \s-1BIO.\s0
.PP
There should be a way to \*(L"rewind\*(R" a read write \s-1BIO\s0 without destroying
its contents.
.PP
The copying operation should not occur after every small read of a large \s-1BIO\s0
to improve efficiency.
.SH "EXAMPLE"
.IX Header "EXAMPLE"
Create a memory \s-1BIO\s0 and write some data to it:
.PP
.Vb 2
\& 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 3
\& char data[] = "Hello World";
\& BIO *mem;
\& 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 4
\& 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 "SEE ALSO"
.IX Header "SEE ALSO"
\&\s-1TBA\s0

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✏️ BIO_get_mem_data.3ssl