Packets: Add SENF_PACKET_PARSER_DEFINE_[FIXED_]FIELDS_OFFSET

Packets/PacketParser.hh

@@ -463,8 +463,37 @@ namespace senf {
         \hideinitializer
      */
 #   define SENF_PACKET_PARSER_DEFINE_FIELDS(fields)                                               \
-    SENF_PACKET_PARSER_I_DEFINE_FIELDS(fields)
+    SENF_PACKET_PARSER_I_DEFINE_FIELDS(0,fields)
         
+    /** \brief Define fields for a dynamically sized parser (with offset)
+
+        Define the fields as specified in \a fields. This macro supports dynamically sized
+        subfields, the resulting parser will be dynamically sized.
+
+        The \a offset argument gives the byte offset at which to start parsing the fields. This
+        helps defining extended parser deriving from a base parser:
+        \code
+           struct ExtendedParser : public BaseParser
+           {
+               SENF_PACKET_PARSER_NO_INIT(ExtendedParser);
+        
+               SENF_PACKET_PARSER_DEFINE_FIELDS_OFFSET(senf::bytes(BaseParser(*this)),
+                 ( ... fields ... ) );
+
+               void init() {
+                   BaseParser::init();
+                   defaultInit();
+                   // other init code
+               }
+           }
+        \endcode
+
+        \ingroup packetparsermacros
+        \hideinitializer
+     */
+#   define SENF_PACKET_PARSER_DEFINE_FIELDS_OFFSET(offset,fields)                                 \
+    SENF_PACKET_PARSER_I_DEFINE_FIELDS(offset,fields)
+
     /** \brief Define fields for a fixed size parser
 
         Define the fields as specified in \a fields. This macro only supports fixed size
@@ -474,7 +503,36 @@ namespace senf {
         \hideinitializer
      */
 #   define SENF_PACKET_PARSER_DEFINE_FIXED_FIELDS(fields)                                         \
-    SENF_PACKET_PARSER_I_DEFINE_FIXED_FIELDS(fields)
+    SENF_PACKET_PARSER_I_DEFINE_FIXED_FIELDS(0,fields)
+
+    /** \brief Define fields for a fixed size parser
+
+        Define the fields as specified in \a fields. This macro only supports fixed size
+        subfields, the resulting parser will also be a fixed size parser.
+
+        The \a offset argument gives the byte offset at which to start parsing the fields. This
+        helps defining extended parser deriving from a base parser:
+        \code
+           struct ExtendedParser : public BaseParser
+           {
+               SENF_PACKET_PARSER_NO_INIT(ExtendedParser);
+
+               SENF_PACKET_PARSER_DEFINE_FIXED_FIELDS_OFFSET(BaseParser::fixed_bytes,
+                 ( ... fields ... ) );
+
+               void init() {
+                   BaseParser::init();
+                   defaultInit();
+                   // other init code
+               }
+           }
+        \endcode
+
+        \ingroup packetparsermacros
+        \hideinitializer
+     */
+#   define SENF_PACKET_PARSER_DEFINE_FIXED_FIELDS_OFFSET(offset,fields)                           \
+    SENF_PACKET_PARSER_I_DEFINE_FIXED_FIELDS(offset,fields)
 
     struct VoidPacketParser 
         : public PacketParserBase

Packets/PacketParser.mpp

@@ -65,8 +65,8 @@
 # define SENF_PACKET_PARSER_I_INITSIZE_C(_0,_1,n,elt)                                             \
      BOOST_PP_IF(n,+,) senf::init_bytes< SENF_PACKET_PARSER_I_GET_TYPE(elt) >::value
 #     
-# define SENF_PACKET_PARSER_I_DEFINE_FIELDS(fields)                                               \
-     size_type offset_0_() const { return 0; }                                                    \
+# define SENF_PACKET_PARSER_I_DEFINE_FIELDS(offset,fields)                                        \
+     size_type offset_0_() const { return offset; }                                               \
      BOOST_PP_SEQ_FOR_EACH_I(SENF_PACKET_PARSER_I_FIELD_C, _, fields)                             \
      size_type bytes() const {                                                                    \
          return BOOST_PP_CAT(offset_,BOOST_PP_CAT(BOOST_PP_SEQ_SIZE(fields),_)) ();               \
@@ -82,8 +82,8 @@
      BOOST_PP_EXPAND(                                                                             \
          SENF_PACKET_PARSER_I_FIXED_FIELD_DISPATCH SENF_PACKET_PARSER_I_UNWRAP(n,elt))
 # 
-# define SENF_PACKET_PARSER_I_DEFINE_FIXED_FIELDS(fields)                                         \
-     static const size_type offset_0_ = 0;                                                        \
+# define SENF_PACKET_PARSER_I_DEFINE_FIXED_FIELDS(offset,fields)                                  \
+     static const size_type offset_0_ = offset;                                                   \
      BOOST_PP_SEQ_FOR_EACH_I(SENF_PACKET_PARSER_I_FIXED_FIELD_C, _, fields)                       \
      static const size_type fixed_bytes =                                                         \
          BOOST_PP_CAT(offset_,BOOST_PP_CAT(BOOST_PP_SEQ_SIZE(fields),_));                         \