first commit, SM2-DSA only

doc/crypto/buffer.pod

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+=pod
+
+=head1 NAME
+
+BUF_MEM_new, BUF_MEM_free, BUF_MEM_grow, BUF_strdup - simple
+character arrays structure
+
+=head1 SYNOPSIS
+
+ #include <openssl/buffer.h>
+
+ BUF_MEM *BUF_MEM_new(void);
+
+ void	BUF_MEM_free(BUF_MEM *a);
+
+ int	BUF_MEM_grow(BUF_MEM *str, int len);
+
+ char *	BUF_strdup(const char *str);
+
+=head1 DESCRIPTION
+
+The buffer library handles simple character arrays. Buffers are used for
+various purposes in the library, most notably memory BIOs.
+
+The library uses the BUF_MEM structure defined in buffer.h:
+
+ typedef struct buf_mem_st
+ {
+        int length;     /* current number of bytes */
+        char *data;
+        int max;        /* size of buffer */
+ } BUF_MEM;
+
+B<length> is the current size of the buffer in bytes, B<max> is the amount of
+memory allocated to the buffer. There are three functions which handle these
+and one "miscellaneous" function.
+
+BUF_MEM_new() allocates a new buffer of zero size.
+
+BUF_MEM_free() frees up an already existing buffer. The data is zeroed
+before freeing up in case the buffer contains sensitive data.
+
+BUF_MEM_grow() changes the size of an already existing buffer to
+B<len>. Any data already in the buffer is preserved if it increases in
+size.
+
+BUF_strdup() copies a null terminated string into a block of allocated
+memory and returns a pointer to the allocated block.
+Unlike the standard C library strdup() this function uses OPENSSL_malloc() and so
+should be used in preference to the standard library strdup() because it can
+be used for memory leak checking or replacing the malloc() function.
+
+The memory allocated from BUF_strdup() should be freed up using the OPENSSL_free()
+function.
+
+=head1 RETURN VALUES
+
+BUF_MEM_new() returns the buffer or NULL on error.
+
+BUF_MEM_free() has no return value.
+
+BUF_MEM_grow() returns zero on error or the new size (i.e. B<len>).
+
+=head1 SEE ALSO
+
+L<bio(3)|bio(3)>
+
+=head1 HISTORY
+
+BUF_MEM_new(), BUF_MEM_free() and BUF_MEM_grow() are available in all
+versions of SSLeay and OpenSSL. BUF_strdup() was added in SSLeay 0.8.
+
+=cut