NAME

       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

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);

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 when it is empty. If the 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 v is non zero then it will return 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 v should be set to a negative value,
       typically -1.

       BIO_get_mem_data() sets 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 bm and sets the close flag to c,
       that is c should be either BIO_CLOSE or BIO_NOCLOSE.  It is a macro.

       BIO_get_mem_ptr() places the underlying BUF_MEM structure in pp. It is a macro.

       BIO_new_mem_buf() creates a memory BIO using len bytes of data at buf, if len is -1 then
       the buf is assumed to be null terminated and its length is determined by 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 not copied first, so the
       supplied area of memory must be unchanged until the BIO is freed.

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 lot 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.

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
       efficiency.

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);

SEE ALSO

       TBA