Android_verify/third_party/android-libs/share/man/man3/BIO_s_mem.3ossl

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.\"
.IX Title "BIO_S_MEM 3ossl"
.TH BIO_S_MEM 3ossl "2024-09-03" "3.3.2" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
BIO_s_secmem, BIO_s_dgram_mem,
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_dgram_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
\&\fBBIO_s_dgram_mem()\fR is a memory \s-1BIO\s0 that respects datagram semantics. A single
call to \fBBIO_write\fR\|(3) will write a single datagram to the memory \s-1BIO. A\s0
subsequent call to \fBBIO_read\fR\|(3) will read the data in that datagram. The
\&\fBBIO_read\fR\|(3) call will never return more data than was written in the original
\&\fBBIO_write\fR\|(3) call even if there were subsequent \fBBIO_write\fR\|(3) calls that
wrote more datagrams. Each successive call to \fBBIO_read\fR\|(3) will read the next
datagram. If a \fBBIO_read\fR\|(3) call supplies a read buffer that is smaller than
the size of the datagram, then the read buffer will be completely filled and the
remaining data from the datagram will be discarded.
.PP
It is not possible to write a zero length datagram. Calling \fBBIO_write\fR\|(3) in
this case will return 0 and no datagrams will be written. Calling \fBBIO_read\fR\|(3)
when there are no datagrams in the \s-1BIO\s0 to read will return a negative result and
the \*(L"retry\*(R" flags will be set (i.e. calling \fBBIO_should_retry\fR\|(3) will return
true). A datagram mem \s-1BIO\s0 will never return true from \fBBIO_eof\fR\|(3).
.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 except \fBBIO_s_dgram_mem()\fR support \fBBIO_gets()\fR and \fBBIO_puts()\fR.
.PP
\&\fBBIO_s_dgram_mem()\fR supports \fBBIO_sendmmsg\fR\|(3) and \fBBIO_recvmmsg\fR\|(3) calls
and calls related to \fB\s-1BIO_ADDR\s0\fR and \s-1MTU\s0 handling similarly to the
\&\fBBIO_s_dgram_pair\fR\|(3).
.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.
Calling this macro will fail for datagram mem BIOs.
.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.
Note the pointer returned by this call is informative, no transfer of ownership
of this memory is implied.  See notes on \fBBIO_set_close()\fR.
.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.
.PP
All of the five functions described above return an error with
\&\fBBIO_s_dgram_mem()\fR.
.SH "NOTES"
.IX Header "NOTES"
Writes to memory BIOs will always succeed if memory is available: that is
their size can grow indefinitely. An exception is \fBBIO_s_dgram_mem()\fR when
\&\fBBIO_set_write_buf_size\fR\|(3) is called on it. In such case the write buffer
size will be fixed and any writes that would overflow the buffer will return
an error.
.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 secmem or dgram \s-1BIO\s0 will give undefined results,
including perhaps a program crash.
.PP
Switching a 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 a 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.
.PP
Calling \fBBIO_set_close()\fR with \s-1BIO_NOCLOSE\s0 orphans the \s-1BUF_MEM\s0 internal to the
\&\s-1BIO,\s0 _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.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBBIO_s_mem()\fR, \fBBIO_s_dgram_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
.PP
Extract the \s-1BUF_MEM\s0 ptr, claim ownership of the internal data and free the \s-1BIO\s0
and \s-1BUF_MEM\s0 structure:
.PP
.Vb 2
\& 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);
.Ve
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2000\-2023 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (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>.