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BIO_s_mem(3)                        OpenSSL                       BIO_s_mem(3)


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(const 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 nul 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

1.0.2h                            2016-05-03                      BIO_s_mem(3)

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