/usr/man/cat.3/BIO_s_mem.3

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.

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BIO_s_mem(3)                 OpenSSL                 BIO_s_mem(3)

     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:

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BIO_s_mem(3)                 OpenSSL                 BIO_s_mem(3)

      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

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See also BIO_get_mem_data(3)
See also BIO_get_mem_ptr(3)
See also BIO_new_mem_buf(3)
See also BIO_set_mem_buf(3)
See also BIO_set_mem_eof_return(3)