9fe9d0461e
Currently on every BIO mem read operation the remaining data is reallocated. This commit solves the issue. BIO mem structure includes additional pointer to the read position. On every read the pointer moves instead of reallocating the memory for the remaining data. Reallocation accures before write and some ioctl operations, if the read pointer doesn't point on the beginning of the buffer. Also the flag is added to rewind the read pointer without losing the data. Reviewed-by: Richard Levitte <levitte@openssl.org> Reviewed-by: Rich Salz <rsalz@openssl.org>
117 lines
4 KiB
Text
117 lines
4 KiB
Text
=pod
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=head1 NAME
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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_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() return 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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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 support BIO_gets() and BIO_puts().
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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. On a read only BIO or if the flag
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BIO_FLAGS_NONCLEAR_RST is set it restores the BIO to its original state and
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the 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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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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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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=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.
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Every read from a read write memory BIO will remove the data just read with
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an internal copy operation, if a BIO contains a lot of data and it is
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read in small chunks the operation can be very slow. The use of a read only
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memory BIO avoids this problem. If the BIO must be read write then adding
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a buffering BIO to the chain will speed up the process.
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Calling BIO_set_mem_buf() on a BIO created with BIO_new_secmem() will
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give undefined results, including perhaps a program crash.
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=head1 BUGS
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There should be an option to set the maximum size of a memory BIO.
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=head1 EXAMPLE
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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;
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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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=head1 SEE ALSO
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TBA
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