Add documentation for the BIO_s_mem pecularities

[openssl.git] / doc / man3 / BIO_s_mem.pod

diff --git a/doc/man3/BIO_s_mem.pod b/doc/man3/BIO_s_mem.pod
index b55ecbfef4f65a78fc7131ea812aa85a1ad0dca2..6d9e747b255d0cb21d0a74c65f47ebca16875ab7 100644 (file)
--- a/doc/man3/BIO_s_mem.pod
+++ b/doc/man3/BIO_s_mem.pod
@@ -56,14 +56,14 @@ zero then it will return B<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 B<v> should be set to a negative value, typically -1.
 
-BIO_get_mem_data() sets B<pp> to a pointer to the start of the memory BIOs data
+BIO_get_mem_data() sets *B<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 B<bm> and sets the
 close flag to B<c>, that is B<c> should be either BIO_CLOSE or BIO_NOCLOSE.
 It is a macro.
 
-BIO_get_mem_ptr() places the underlying BUF_MEM structure in B<pp>. It is
+BIO_get_mem_ptr() places the underlying BUF_MEM structure in *B<pp>. It is
 a macro.
 
 BIO_new_mem_buf() creates a memory BIO using B<len> bytes of data at B<buf>,
@@ -88,6 +88,22 @@ 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.
 
+Switching the memory BIO from read write to read only is not supported and
+can give undefined results including a program crash. There are two notable
+exceptions to the rule. The first one is to assign a static memory buffer
+immediately after BIO creation and set the BIO as read only.
+
+The other supported sequence is to start with read write BIO then temporarily
+switch it to read only and call BIO_reset() on the read only BIO immediately
+before switching it back to read write. Before the BIO is freed it must be
+switched back to the read write mode.
+
+Calling BIO_get_mem_ptr() on read only BIO will return a BUF_MEM that
+contains only the remaining data to be read. If the close status of the
+BIO is set to BIO_NOCLOSE, before freeing the BUF_MEM the data pointer
+in it must be set to NULL as the data pointer does not point to an
+allocated memory.
+
 =head1 BUGS
 
 There should be an option to set the maximum size of a memory BIO.
@@ -126,7 +142,7 @@ BIO_new_mem_buf() returns a valid B<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
+Licensed under the Apache License 2.0 (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
 L<https://www.openssl.org/source/license.html>.