[3180] Updated Developer Guide with an info about option parsing callbacks.

doc/devel/mainpage.dox

@@ -53,12 +53,14 @@
  *   - @subpage dhcpv4Session
  *   - @subpage dhcpv4ConfigParser
  *   - @subpage dhcpv4ConfigInherit
+ *   - @subpage dhcpv4OptionsParse
  *   - @subpage dhcpv4Other
  * - @subpage dhcp6
  *   - @subpage dhcpv6Session
  *   - @subpage dhcpv6ConfigParser
  *   - @subpage dhcpv6ConfigInherit
  *   - @subpage dhcpv6DDNSIntegration
+ *   - @subpage dhcpv6OptionsParse
  *   - @subpage dhcpv6Other
  * - @subpage libdhcp
  *   - @subpage libdhcpIntro

src/bin/dhcp4/dhcp4.dox

@@ -1,4 +1,4 @@
-// Copyright (C) 2012  Internet Systems Consortium, Inc. ("ISC")
+// Copyright (C) 2012-2013  Internet Systems Consortium, Inc. ("ISC")
 //
 // Permission to use, copy, modify, and/or distribute this software for any
 // purpose with or without fee is hereby granted, provided that the above
@@ -79,6 +79,11 @@ See \ref dhcpv6ConfigParser.
 Configuration inheritance in DHCPv4 follows exactly the same logic as its DHCPv6
 counterpart. See \ref dhcpv6ConfigInherit.
 
+@section dhcpv4OptionsParse Custom functions to parse message options
+
+The DHCPv4 server uses the same logic to supply custom callback function to
+parse message option as DHCPv6 server implementation. See \ref dhcpv6OptionsParse.
+
 @section dhcpv4Other Other DHCPv4 topics
 
  For hooks API support in DHCPv4, see @ref dhcpv4Hooks.

src/bin/dhcp6/dhcp6.dox

@@ -167,6 +167,29 @@ Once the configuration is implemented, these constants will be removed.
 
  @todo Add section about setting up options and their definitions with bindctl.
 
+@section dhcpv6OptionsParse Custom functions to parse message options
+
+The DHCPv6 server implementation provides a generic support to define option
+formats and set option values. A number of options formats have been defined
+for standard options in libdhcp++. However, the formats for vendor specific
+options are dynamically configured by the server's administrator and thus can't
+be stored in libdhcp++. Such option formats are stored in the
+@c isc::dhcp::CfgMgr. The libdhcp++ provides functions for recursive parsing
+of options which may be encapsulated by other options up to the any level of
+encapsulation but these functions are unaware of the option formats defined
+in the @c isc::dhcp::CfgMgr because they belong to a different library.
+Therefore, the generic functions @c isc::dhcp::LibDHCP::unpackOptions4 and
+@c isc::dhcp::LibDHCP::unpackOptions6 are only useful to parse standard
+options which definitions are provided in the libdhcp++. In order to overcome
+this problem a callback mechanism has been implemented in @c Option and @c Pkt6
+classes. By installing a callback function on the instance of the @c Pkt6 the
+server may provide a custom implementation of the options parsing algorithm.
+This callback function will take precedence over the @c LibDHCP::unpackOptions6
+and @c LibDHCP::unpackOptions4 functions. With this approach, the callback is
+implemented within the context of the server and it has access to all objects
+which define its configuration (including dynamically created option
+definitions).
+
  @section dhcpv6Other Other DHCPv6 topics
 
  For hooks API support in DHCPv6, see @ref dhcpv6Hooks.