From 6df67897441942181bf4a2afcb6bb79c0c5fa08d Mon Sep 17 00:00:00 2001
From: Aditya Sharma <aditya.sharma.met19@itbhu.ac.in>
Date: Fri, 21 Feb 2025 00:24:12 +0530
Subject: [PATCH] Enable Length-Prefixed TLVs through Generator

This change allows adding a length prefix to a serialized TLV. It will
be particularly useful for serializing all 'scb_chan' entries in
the 'emergency.recover' file.

Key Changes:
 - Removed the need to loop in towire_tlv and fromwire_tlv, so the if conditions have been modified accordingly.
 - During serialization, the length of the TLV is calculated before appending it, and it is stored in a temporary variable.
 - For fromwire_tlv, only a simple length adjustment is required, and no loop is needed here either.
---
 tools/gen/header_template |  2 +-
 tools/gen/impl_template   | 15 ++++++++++++---
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/tools/gen/header_template b/tools/gen/header_template
index bbfe0df97..5ceb9df32 100644
--- a/tools/gen/header_template
+++ b/tools/gen/header_template
@@ -70,7 +70,7 @@ struct ${struct.struct_name()} {
         % if bool(f.len_field_of):
 <% continue %>
         % endif
-            % if f.is_varlen() and f.type_obj.is_varsize():
+            % if not f.type_obj.is_tlv() and f.is_varlen() and f.type_obj.is_varsize():
         ${f.type_obj.type_name()} **${f.name};
             % elif f.is_varlen() or f.type_obj.is_varsize():
         ${f.type_obj.type_name()} *${f.name};
diff --git a/tools/gen/impl_template b/tools/gen/impl_template
index 7b9011e1d..c3b97d5f5 100644
--- a/tools/gen/impl_template
+++ b/tools/gen/impl_template
@@ -51,7 +51,7 @@ bool ${enum_set['name']}_is_defined(u16 type)
 ## START PARTIALS
 ## Subtype and TLV-msg towire_
 <%def name="towire_subtype_field(fieldname, f, type_obj, is_single_ptr, ptr)">\
-% if f.is_array() or f.is_varlen():
+% if not f.type_obj.is_tlv() and (f.is_array() or f.is_varlen()):
     % if type_obj.has_array_helper():
 towire_${type_obj.name}_array(${ptr}, ${fieldname}, ${f.size('tal_count(' + fieldname + ')')});
     % else:
@@ -82,7 +82,7 @@ towire_${type_obj.name}(${ptr}, ${'' if type_obj.is_assignable() or type_obj.is_
     if f.type_obj.is_varsize():
 	typename += ' *'
 %>\
-% if f.is_array() or f.is_varlen():
+% if not f.type_obj.is_tlv() and (f.is_array() or f.is_varlen()):
     % if f.type_obj.has_array_helper():
     ## We assume array helpers only deal with things literally transcribed!!
 	% if f.is_varlen():
@@ -116,8 +116,10 @@ ${fieldname} = ${f.size('*plen')} ? tal_arr(${ctx}, ${typename}, 0) : NULL;
     % endif
     % if f.type_obj.is_assignable():
 ${ f.name if f.len_field_of else fieldname} = fromwire_${type_}(cursor, plen);
-    % elif f.type_obj.is_varsize():
+    % elif f.type_obj.is_varsize() and not f.type_obj.is_tlv():
 ${fieldname} = fromwire_${type_}(${ctx}, cursor, plen);
+    % elif f.type_obj.is_tlv() and f.is_varlen():
+${fieldname} = fromwire_${type_}(${ctx}, cursor, &(size_t){(size_t)${f.size()}});
     % else:
 fromwire_${type_}(cursor, plen, &${fieldname});
     % endif
@@ -138,7 +140,14 @@ fromwire_${type_}(cursor, plen, &${fieldname});
 ${static}void towire_${subtype.name}(u8 **p, const ${subtype.type_name()} *${subtype.name})
 {
 	% for f in subtype.get_len_fields():
+	 % if not subtype.find_data_field(f.len_field_of).type_obj.is_tlv():  # Check if this signify length of TLV.
 	${f.type_obj.type_name()} ${f.name} = tal_count(${subtype.name}->${f.len_field_of});
+	 % else:
+	 /* Length of serialized tlv. */
+	u8 *tmp = tal_arr(tmpctx, u8, 0);
+	towire_tlv_${subtype.find_data_field(f.len_field_of).type_obj.name}(&tmp, ${subtype.name}->${f.len_field_of});
+	${f.type_obj.type_name()} ${f.name} = tal_bytelen(tmp);
+   	 % endif
 	% endfor
 
 	% for f in subtype.fields.values():