diff options
author | Dr. Stephen Henson <steve@openssl.org> | 2000-09-10 01:52:26 +0000 |
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committer | Dr. Stephen Henson <steve@openssl.org> | 2000-09-10 01:52:26 +0000 |
commit | d7b9c76c72bd6e744db2070d148738941ba38305 (patch) | |
tree | 46480be11f8b6bac37f3f2052d6b262261a85a91 /doc/crypto/BIO_s_mem.pod | |
parent | 0baed24c1b2d9a1e53d9f81cf805ac65d68096b3 (diff) |
More preliminary BIO docs...
Incomplete and possibly inaccurate. Hope somone is
checking these :-)
Diffstat (limited to 'doc/crypto/BIO_s_mem.pod')
-rw-r--r-- | doc/crypto/BIO_s_mem.pod | 116 |
1 files changed, 116 insertions, 0 deletions
diff --git a/doc/crypto/BIO_s_mem.pod b/doc/crypto/BIO_s_mem.pod new file mode 100644 index 0000000000..9eb1fc056a --- /dev/null +++ b/doc/crypto/BIO_s_mem.pod @@ -0,0 +1,116 @@ +=pod + +=head1 NAME + + BIO_s_mem - memory BIO + +=head1 SYNOPSIS + + #include <openssl/bio.h> + + BIO_METHOD * BIO_s_mem(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(void *buf, int len); + +=head1 DESCRIPTION + +BIO_s_mem() return the memory BIO method function. + +A memory BIO is a source/sink BIO which uses memory for its I/O. Data +written to a memory BIO is stored in a BUF_MEM structure which is extended +as appropriate to accommodate the stored data. + +Any data written to a memory BIO can be recalled by reading from it. +Unless the memory BIO is read only any data read from it is deleted from +the BIO. + +Memory BIOs support BIO_gets() and BIO_puts(). + +If the BIO_CLOSE flag is set when a memory BIO is freed then the underlying +BUF_MEM structure is also freed. + +Calling BIO_reset() on a read write memory BIO clears any data in it. On a +read only BIO it restores the BIO to its original state and the read only +data can be read again. + +BIO_eof() is true if no data is in the BIO. + +BIO_ctrl_pending() returns the number of bytes currently stored. + +BIO_set_mem_eof_return() sets the behaviour of memory BIO B<b> when it is +empty. If the B<v> is zero then an empty memory BIO will return EOF (that is +it will return zero and BIO_should_retry(b) will be false. If B<v> is non +zero then it will return B<v> 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 B<v> should be set to a negative value, typically -1. + +BIO_get_mem_data() sets B<pp> 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. + +BIO_set_mem_buf() sets the internal BUF_MEM structure to B<bm> and sets the +close flag to B<c>, that is B<c> should be either BIO_CLOSE or BIO_NOCLOSE. +It is a macro. + +BIO_get_mem_ptr() places the underlying BUF_MEM structure in B<pp>. It is +a macro. + +BIO_new_mem_buf() creates a memory BIO using B<len> bytes of data at B<buf>, +if B<len> is -1 then the B<buf> is assumed to be null terminated and its +length is determined by B<strlen>. The BIO 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 BIO. The +supplied data is read directly from the supplied buffer: it is B<not> copied +first, so the supplied area of memory must be unchanged until the BIO is freed. + +=head1 NOTES + +Writes to memory BIOs will always succeed if memory is available: that is +their size can grow indefinitely. + +Every read from a read write memory BIO will remove the data just read with +an internal copy operation, if a BIO contains a lots of data and it is +read in small chunks the operation can be very slow. The use of a read only +memory BIO avoids this problem. If the BIO must be read write then adding +a buffering BIO to the chain will speed up the process. + +=head1 BUGS + +There should be an option to set the maximum size of a memory BIO. + +There should be a way to "rewind" a read write BIO without destroying +its contents. + +The copying operation should not occur after every small read of a large BIO +to improve efficieny. + +There shoy + +=head1 EXAMPLE + +Create a memory BIO and write some data to it: + + BIO *mem = BIO_new(BIO_s_mem()); + BIO_puts(mem, "Hello World\n"); + +Create a read only memory BIO: + + char data[] = "Hello World"; + BIO *mem; + mem = BIO_new_mem_buf(data, -1); + +Extract the BUF_MEM structure from a memory BIO and then free up the BIO: + + 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); + + +=head1 SEE ALSO + +TBA |