pyln-proto: write out length of arrays of subtypes to wire

We weren't writing out the length of a nested subtype's
dynamicarraylenght, now we do. The trick is to iterate through the
fields on a subtype (since the length field is added separately)
and to also iterate down through the otherfield values as we 'descend'

contrib/pyln-proto/pyln/proto/message/array_types.py

@@ -48,9 +48,16 @@ wants an array of some type.
 
         return [self.elemtype.val_to_py(i, otherfields) for i in v]
 
-    def write(self, io_out: BufferedIOBase, v: List[Any], otherfields: Dict[str, Any]) -> None:
-        for i in v:
-            self.elemtype.write(io_out, i, otherfields)
+    def write(self, io_out: BufferedIOBase, vals: List[Any], otherfields: Dict[str, Any]) -> None:
+        name = self.name.split('.')[1]
+        if otherfields and name in otherfields:
+            otherfields = otherfields[name]
+        for i, val in enumerate(vals):
+            if isinstance(otherfields, list) and len(otherfields) > i:
+                fields = otherfields[i]
+            else:
+                fields = otherfields
+            self.elemtype.write(io_out, val, fields)
 
     def read_arr(self, io_in: BufferedIOBase, otherfields: Dict[str, Any], arraysize: Optional[int]) -> List[Any]:
         """arraysize None means take rest of io entirely and exactly"""
@@ -179,7 +186,7 @@ they're implied by the length of other fields"""
                 if mylen != len(otherfields[lens.name]):
                     return [fieldname]
             # Field might be missing!
-            if lens.name in otherfields:
+            if otherfields and lens.name in otherfields:
                 mylen = len(otherfields[lens.name])
         return []
 

contrib/pyln-proto/pyln/proto/message/message.py

@@ -297,10 +297,17 @@ other types.  Since 'msgtype' is almost identical, it inherits from this too.
 
     def write(self, io_out: BufferedIOBase, v: Dict[str, Any], otherfields: Dict[str, Any]) -> None:
         self._raise_if_badvals(v)
-        for fname, val in v.items():
-            field = self.find_field(fname)
-            assert field
-            field.fieldtype.write(io_out, val, otherfields)
+        for f in self.fields:
+            if f.name in v:
+                val = v[f.name]
+            else:
+                if f.option is not None:
+                    raise ValueError("Missing field {} {}".format(f.name, otherfields))
+                val = None
+
+            if self.name in otherfields:
+                otherfields = otherfields[self.name]
+            f.fieldtype.write(io_out, val, otherfields)
 
     def read(self, io_in: BufferedIOBase, otherfields: Dict[str, Any]) -> Optional[Dict[str, Any]]:
         vals = {}

contrib/pyln-proto/tests/test_message.py

@@ -90,6 +90,29 @@ def test_subtype():
     assert m.missing_fields()
 
 
+def test_subtype_array():
+    ns = MessageNamespace()
+    ns.load_csv(['msgtype,tx_signatures,1',
+                 'msgdata,tx_signatures,num_witnesses,u16,',
+                 'msgdata,tx_signatures,witness_stack,witness_stack,num_witnesses',
+                 'subtype,witness_stack',
+                 'subtypedata,witness_stack,num_input_witness,u16,',
+                 'subtypedata,witness_stack,witness_element,witness_element,num_input_witness',
+                 'subtype,witness_element',
+                 'subtypedata,witness_element,len,u16,',
+                 'subtypedata,witness_element,witness,byte,len'])
+
+    for test in [["tx_signatures witness_stack="
+                 "[{witness_element=[{witness=3045022100ac0fdee3e157f50be3214288cb7f11b03ce33e13b39dadccfcdb1a174fd3729a02200b69b286ac9f0fc5c51f9f04ae5a9827ac11d384cc203a0eaddff37e8d15c1ac01},{witness=02d6a3c2d0cf7904ab6af54d7c959435a452b24a63194e1c4e7c337d3ebbb3017b}]}]",
+                  bytes.fromhex('00010001000200483045022100ac0fdee3e157f50be3214288cb7f11b03ce33e13b39dadccfcdb1a174fd3729a02200b69b286ac9f0fc5c51f9f04ae5a9827ac11d384cc203a0eaddff37e8d15c1ac01002102d6a3c2d0cf7904ab6af54d7c959435a452b24a63194e1c4e7c337d3ebbb3017b')]]:
+        m = Message.from_str(ns, test[0])
+        assert m.to_str() == test[0]
+        buf = io.BytesIO()
+        m.write(buf)
+        assert buf.getvalue().hex() == test[1].hex()
+        assert Message.read(ns, io.BytesIO(test[1])).to_str() == test[0]
+
+
 def test_tlv():
     ns = MessageNamespace()
     ns.load_csv(['msgtype,test1,1',