mirror of https://github.com/openssl/openssl
210 lines
8.4 KiB
Plaintext
210 lines
8.4 KiB
Plaintext
=pod
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=head1 NAME
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BIO_s_secmem, BIO_s_dgram_mem,
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BIO_s_mem, BIO_set_mem_eof_return, BIO_get_mem_data, BIO_set_mem_buf,
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BIO_get_mem_ptr, BIO_new_mem_buf - memory BIO
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=head1 SYNOPSIS
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#include <openssl/bio.h>
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const BIO_METHOD *BIO_s_mem(void);
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const BIO_METHOD *BIO_s_dgram_mem(void);
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const BIO_METHOD *BIO_s_secmem(void);
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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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BIO *BIO_new_mem_buf(const void *buf, int len);
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=head1 DESCRIPTION
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BIO_s_mem() returns the memory BIO method function.
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A memory BIO is a source/sink BIO which uses memory for its I/O. Data
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written to a memory BIO is stored in a BUF_MEM structure which is extended
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as appropriate to accommodate the stored data.
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BIO_s_secmem() is like BIO_s_mem() except that the secure heap is used
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for buffer storage.
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BIO_s_dgram_mem() is a memory BIO that respects datagram semantics. A single
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call to L<BIO_write(3)> will write a single datagram to the memory BIO. A
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subsequent call to L<BIO_read(3)> will read the data in that datagram. The
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L<BIO_read(3)> call will never return more data than was written in the original
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L<BIO_write(3)> call even if there were subsequent L<BIO_write(3)> calls that
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wrote more datagrams. Each successive call to L<BIO_read(3)> will read the next
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datagram. If a L<BIO_read(3)> call supplies a read buffer that is smaller than
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the size of the datagram, then the read buffer will be completely filled and the
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remaining data from the datagram will be discarded.
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It is not possible to write a zero length datagram. Calling L<BIO_write(3)> in
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this case will return 0 and no datagrams will be written. Calling L<BIO_read(3)>
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when there are no datagrams in the BIO to read will return a negative result and
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the "retry" flags will be set (i.e. calling L<BIO_should_retry(3)> will return
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true). A datagram mem BIO will never return true from L<BIO_eof(3)>.
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Any data written to a memory BIO can be recalled by reading from it.
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Unless the memory BIO is read only any data read from it is deleted from
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the BIO.
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Memory BIOs except BIO_s_dgram_mem() support BIO_gets() and BIO_puts().
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BIO_s_dgram_mem() supports L<BIO_sendmmsg(3)> and L<BIO_recvmmsg(3)> calls
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and calls related to B<BIO_ADDR> and MTU handling similarly to the
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L<BIO_s_dgram_pair(3)>.
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If the BIO_CLOSE flag is set when a memory BIO is freed then the underlying
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BUF_MEM structure is also freed.
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Calling BIO_reset() on a read write memory BIO clears any data in it if the
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flag BIO_FLAGS_NONCLEAR_RST 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 BIO it similarly restores the BIO to
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its original state and the read only data can be read again.
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BIO_eof() is true if no data is in the BIO.
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BIO_ctrl_pending() returns the number of bytes currently stored.
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BIO_set_mem_eof_return() sets the behaviour of memory BIO B<b> when it is
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empty. If the B<v> is zero then an empty memory BIO will return EOF (that is
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it will return zero and BIO_should_retry(b) will be false. If B<v> is non
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zero then it will return B<v> 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 B<v> should be set to a negative value, typically -1.
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Calling this macro will fail for datagram mem BIOs.
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BIO_get_mem_data() sets *B<pp> 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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Note the pointer returned by this call is informative, no transfer of ownership
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of this memory is implied. See notes on BIO_set_close().
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BIO_set_mem_buf() sets the internal BUF_MEM structure to B<bm> and sets the
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close flag to B<c>, that is B<c> should be either BIO_CLOSE or BIO_NOCLOSE.
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It is a macro.
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BIO_get_mem_ptr() places the underlying BUF_MEM structure in *B<pp>. It is
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a macro.
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BIO_new_mem_buf() creates a memory BIO using B<len> bytes of data at B<buf>,
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if B<len> is -1 then the B<buf> is assumed to be nul terminated and its
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length is determined by B<strlen>. The BIO 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 BIO. The
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supplied data is read directly from the supplied buffer: it is B<not> copied
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first, so the supplied area of memory must be unchanged until the BIO is freed.
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All of the five functions described above return an error with
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BIO_s_dgram_mem().
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=head1 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. An exception is BIO_s_dgram_mem() when
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L<BIO_set_write_buf_size(3)> is called on it. In such case the write buffer
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size will be fixed and any writes that would overflow the buffer will return
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an error.
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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 BIO will have to move the unread data with an internal
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copy operation, if a BIO 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 BIO to the chain can speed up the process.
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Calling BIO_set_mem_buf() on a secmem or dgram BIO will give undefined results,
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including perhaps a program crash.
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Switching a memory BIO 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 BIO creation and set the BIO as read only.
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The other supported sequence is to start with a read write BIO then temporarily
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switch it to read only and call BIO_reset() on the read only BIO immediately
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before switching it back to read write. Before the BIO is freed it must be
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switched back to the read write mode.
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Calling BIO_get_mem_ptr() on read only BIO will return a BUF_MEM that
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contains only the remaining data to be read. If the close status of the
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BIO is set to BIO_NOCLOSE, before freeing the BUF_MEM the data pointer
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in it must be set to NULL as the data pointer does not point to an
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allocated memory.
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Calling BIO_reset() on a read write memory BIO with BIO_FLAGS_NONCLEAR_RST
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flag set can have unexpected outcome when the reads and writes to the
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BIO are intertwined. As documented above the BIO 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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Calling BIO_get_mem_ptr() prior to a BIO_reset() call with
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BIO_FLAGS_NONCLEAR_RST set has the same effect as a write operation.
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Calling BIO_set_close() with BIO_NOCLOSE orphans the BUF_MEM internal to the
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BIO, _not_ its actual data buffer. See the examples section for the proper
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method for claiming ownership of the data pointer for a deferred free operation.
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=head1 RETURN VALUES
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BIO_s_mem(), BIO_s_dgram_mem() and BIO_s_secmem() return a valid memory
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B<BIO_METHOD> structure.
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BIO_set_mem_eof_return(), BIO_set_mem_buf() and BIO_get_mem_ptr()
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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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BIO_get_mem_data() returns the total number of bytes available on success,
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0 if b is NULL, or a negative value in case of other errors.
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BIO_new_mem_buf() returns a valid B<BIO> structure on success or NULL on error.
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=head1 EXAMPLES
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Create a memory BIO and write some data to it:
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BIO *mem = BIO_new(BIO_s_mem());
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BIO_puts(mem, "Hello World\n");
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Create a read only memory BIO:
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char data[] = "Hello World";
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BIO *mem = BIO_new_mem_buf(data, -1);
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Extract the BUF_MEM structure from a memory BIO and then free up the BIO:
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BUF_MEM *bptr;
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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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Extract the BUF_MEM ptr, claim ownership of the internal data and free the BIO
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and BUF_MEM structure:
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BUF_MEM *bptr;
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char *data;
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BIO_get_mem_data(bio, &data);
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BIO_get_mem_ptr(bio, &bptr);
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BIO_set_close(mem, BIO_NOCLOSE); /* So BIO_free orphans BUF_MEM */
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BIO_free(bio);
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bptr->data = NULL; /* Tell BUF_MEM to orphan data */
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BUF_MEM_free(bptr);
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...
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free(data);
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=head1 COPYRIGHT
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Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). 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 LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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