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
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);
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
If the BIO_CLOSE flag is set when a memory BIO is freed then the underlying BUF_MEM structure is also freed.
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.
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.
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);