forked from cory/tildefriends
298 lines
11 KiB
Groff
298 lines
11 KiB
Groff
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.\" ========================================================================
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.\"
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.IX Title "BIO_S_MEM 3"
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.TH BIO_S_MEM 3 "2020-04-21" "1.1.1g" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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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
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/bio.h>
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\&
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\& const BIO_METHOD *BIO_s_mem(void);
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\& const BIO_METHOD *BIO_s_secmem(void);
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\&
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\& BIO_set_mem_eof_return(BIO *b, int v)
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\& long BIO_get_mem_data(BIO *b, char **pp)
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\& BIO_set_mem_buf(BIO *b, BUF_MEM *bm, int c)
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\& BIO_get_mem_ptr(BIO *b, BUF_MEM **pp)
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\&
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\& BIO *BIO_new_mem_buf(const void *buf, int len);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fBBIO_s_mem()\fR returns the memory \s-1BIO\s0 method function.
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.PP
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A memory \s-1BIO\s0 is a source/sink \s-1BIO\s0 which uses memory for its I/O. Data
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written to a memory \s-1BIO\s0 is stored in a \s-1BUF_MEM\s0 structure which is extended
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as appropriate to accommodate the stored data.
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.PP
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\&\fBBIO_s_secmem()\fR is like \fBBIO_s_mem()\fR except that the secure heap is used
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for buffer storage.
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.PP
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Any data written to a memory \s-1BIO\s0 can be recalled by reading from it.
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Unless the memory \s-1BIO\s0 is read only any data read from it is deleted from
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the \s-1BIO.\s0
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.PP
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Memory BIOs support \fBBIO_gets()\fR and \fBBIO_puts()\fR.
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.PP
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If the \s-1BIO_CLOSE\s0 flag is set when a memory \s-1BIO\s0 is freed then the underlying
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\&\s-1BUF_MEM\s0 structure is also freed.
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.PP
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Calling \fBBIO_reset()\fR on a read write memory \s-1BIO\s0 clears any data in it if the
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flag \s-1BIO_FLAGS_NONCLEAR_RST\s0 is not set, otherwise it just restores the read
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pointer to the state it was just after the last write was performed and the
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data can be read again. On a read only \s-1BIO\s0 it similarly restores the \s-1BIO\s0 to
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its original state and the read only data can be read again.
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.PP
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\&\fBBIO_eof()\fR is true if no data is in the \s-1BIO.\s0
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.PP
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\&\fBBIO_ctrl_pending()\fR returns the number of bytes currently stored.
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.PP
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\&\fBBIO_set_mem_eof_return()\fR sets the behaviour of memory \s-1BIO\s0 \fBb\fR when it is
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empty. If the \fBv\fR is zero then an empty memory \s-1BIO\s0 will return \s-1EOF\s0 (that is
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it will return zero and BIO_should_retry(b) will be false. If \fBv\fR is non
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zero then it will return \fBv\fR when it is empty and it will set the read retry
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flag (that is BIO_read_retry(b) is true). To avoid ambiguity with a normal
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positive return value \fBv\fR should be set to a negative value, typically \-1.
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.PP
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\&\fBBIO_get_mem_data()\fR sets *\fBpp\fR to a pointer to the start of the memory BIOs data
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and returns the total amount of data available. It is implemented as a macro.
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.PP
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\&\fBBIO_set_mem_buf()\fR sets the internal \s-1BUF_MEM\s0 structure to \fBbm\fR and sets the
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close flag to \fBc\fR, that is \fBc\fR should be either \s-1BIO_CLOSE\s0 or \s-1BIO_NOCLOSE.\s0
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It is a macro.
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.PP
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\&\fBBIO_get_mem_ptr()\fR places the underlying \s-1BUF_MEM\s0 structure in *\fBpp\fR. It is
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a macro.
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.PP
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\&\fBBIO_new_mem_buf()\fR creates a memory \s-1BIO\s0 using \fBlen\fR bytes of data at \fBbuf\fR,
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if \fBlen\fR is \-1 then the \fBbuf\fR is assumed to be nul terminated and its
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length is determined by \fBstrlen\fR. The \s-1BIO\s0 is set to a read only state and
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as a result cannot be written to. This is useful when some data needs to be
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made available from a static area of memory in the form of a \s-1BIO.\s0 The
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supplied data is read directly from the supplied buffer: it is \fBnot\fR copied
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first, so the supplied area of memory must be unchanged until the \s-1BIO\s0 is freed.
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.SH "NOTES"
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.IX Header "NOTES"
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Writes to memory BIOs will always succeed if memory is available: that is
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their size can grow indefinitely.
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.PP
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Every write after partial read (not all data in the memory buffer was read)
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to a read write memory \s-1BIO\s0 will have to move the unread data with an internal
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copy operation, if a \s-1BIO\s0 contains a lot of data and it is read in small
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chunks intertwined with writes the operation can be very slow. Adding
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a buffering \s-1BIO\s0 to the chain can speed up the process.
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.PP
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Calling \fBBIO_set_mem_buf()\fR on a \s-1BIO\s0 created with \fBBIO_new_secmem()\fR will
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give undefined results, including perhaps a program crash.
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.PP
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Switching the memory \s-1BIO\s0 from read write to read only is not supported and
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can give undefined results including a program crash. There are two notable
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exceptions to the rule. The first one is to assign a static memory buffer
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immediately after \s-1BIO\s0 creation and set the \s-1BIO\s0 as read only.
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.PP
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The other supported sequence is to start with read write \s-1BIO\s0 then temporarily
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switch it to read only and call \fBBIO_reset()\fR on the read only \s-1BIO\s0 immediately
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before switching it back to read write. Before the \s-1BIO\s0 is freed it must be
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switched back to the read write mode.
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.PP
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Calling \fBBIO_get_mem_ptr()\fR on read only \s-1BIO\s0 will return a \s-1BUF_MEM\s0 that
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contains only the remaining data to be read. If the close status of the
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\&\s-1BIO\s0 is set to \s-1BIO_NOCLOSE,\s0 before freeing the \s-1BUF_MEM\s0 the data pointer
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in it must be set to \s-1NULL\s0 as the data pointer does not point to an
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allocated memory.
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.PP
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Calling \fBBIO_reset()\fR on a read write memory \s-1BIO\s0 with \s-1BIO_FLAGS_NONCLEAR_RST\s0
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flag set can have unexpected outcome when the reads and writes to the
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\&\s-1BIO\s0 are intertwined. As documented above the \s-1BIO\s0 will be reset to the
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state after the last completed write operation. The effects of reads
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preceding that write operation cannot be undone.
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.PP
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Calling \fBBIO_get_mem_ptr()\fR prior to a \fBBIO_reset()\fR call with
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\&\s-1BIO_FLAGS_NONCLEAR_RST\s0 set has the same effect as a write operation.
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.SH "BUGS"
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.IX Header "BUGS"
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There should be an option to set the maximum size of a memory \s-1BIO.\s0
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fBBIO_s_mem()\fR and \fBBIO_s_secmem()\fR return a valid memory \fB\s-1BIO_METHOD\s0\fR structure.
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.PP
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\&\fBBIO_set_mem_eof_return()\fR, \fBBIO_set_mem_buf()\fR and \fBBIO_get_mem_ptr()\fR
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return 1 on success or a value which is less than or equal to 0 if an error occurred.
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.PP
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\&\fBBIO_get_mem_data()\fR returns the total number of bytes available on success,
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0 if b is \s-1NULL,\s0 or a negative value in case of other errors.
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.PP
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\&\fBBIO_new_mem_buf()\fR returns a valid \fB\s-1BIO\s0\fR structure on success or \s-1NULL\s0 on error.
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.SH "EXAMPLES"
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.IX Header "EXAMPLES"
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Create a memory \s-1BIO\s0 and write some data to it:
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.PP
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.Vb 1
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\& BIO *mem = BIO_new(BIO_s_mem());
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\&
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\& BIO_puts(mem, "Hello World\en");
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.Ve
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.PP
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Create a read only memory \s-1BIO:\s0
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.PP
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.Vb 2
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\& char data[] = "Hello World";
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\& BIO *mem = BIO_new_mem_buf(data, \-1);
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.Ve
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.PP
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Extract the \s-1BUF_MEM\s0 structure from a memory \s-1BIO\s0 and then free up the \s-1BIO:\s0
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.PP
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.Vb 1
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\& BUF_MEM *bptr;
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\&
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\& BIO_get_mem_ptr(mem, &bptr);
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\& BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free() leaves BUF_MEM alone */
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\& BIO_free(mem);
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.Ve
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2000\-2019 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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