mirror of
https://github.com/openssl/openssl.git
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116 lines
3.8 KiB
Plaintext
116 lines
3.8 KiB
Plaintext
=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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BIO_METHOD * BIO_s_mem(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(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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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. On a
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read only BIO it restores the BIO to its original state and the read only
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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 null 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 lots 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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=head1 BUGS
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There should be an option to set the maximum size of a memory BIO.
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There should be a way to "rewind" a read write BIO without destroying
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its contents.
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The copying operation should not occur after every small read of a large BIO
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to improve efficiency.
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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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