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BIO_S_MEM(3) OpenSSL BIO_S_MEM(3)
 

BIO_s_secmem, 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

 #include <openssl/bio.h>
 const BIO_METHOD *BIO_s_mem(void);
 const BIO_METHOD *BIO_s_secmem(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);

BIO_s_mem() returns 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.
BIO_s_secmem() is like BIO_s_mem() except that the secure heap is used for buffer storage.
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 if the flag BIO_FLAGS_NONCLEAR_RST is not set. On a read only BIO or if the flag BIO_FLAGS_NONCLEAR_RST is set it restores the BIO to its original state and the 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.

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.
Calling BIO_set_mem_buf() on a BIO created with BIO_new_secmem() will give undefined results, including perhaps a program crash.

There should be an option to set the maximum size of a memory BIO.

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 = 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);

BIO_s_mem() and BIO_s_secmem() return a valid memory BIO_METHOD structure.
BIO_set_mem_eof_return(), BIO_get_mem_data(), BIO_set_mem_buf() and BIO_get_mem_ptr() return 1 on success or a value which is less than or equal to 0 if an error occurred.
BIO_new_mem_buf() returns a valid BIO structure on success or NULL on error.

Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.
2018-11-20 1.1.1a

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