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BIO_set_mem_buf.3
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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>.
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