Enable checksum setting without verification

ref #240

rflx/pyrflx/typevalue.py

@@ -555,6 +555,7 @@ def __init__(
             self._last_field = INITIAL.name
         else:
             self._preset_fields(INITIAL.name)
+        self.message_last_name = state.last_name if state else Last("Message")
 
     def clone(self) -> "MessageValue":
         return MessageValue(
@@ -949,6 +950,14 @@ def valid_path(value_range: ValueRange) -> bool:
                 return False
         return True
 
+    def update_checksums(self) -> None:
+        # ISSUE: Componolit/RecordFlux#240
+        self._simplified_mapping.update({ValidChecksum(f): TRUE for f in self._checksums})
+        for checksum in self._checksums.values():
+            self._is_checksum_settable(checksum)
+            checksum_value = self._calculate_checksum(checksum)
+            self._fields[checksum.field_name].typeval.assign(checksum_value)
+
     def _set_checksum(self, checksum: "MessageValue.Checksum") -> None:
         self._fields[checksum.field_name].typeval.assign(0)
         checksum.calculated = True
@@ -1077,7 +1086,7 @@ def valid_message(self) -> bool:
             bool(self.valid_fields)
             and self._next_field(self.valid_fields[-1]) == FINAL.name
             and all(
-                self._is_checksum_settable(checksum)
+                (self._is_checksum_settable(checksum) or self._skip_verification)
                 and self._calculate_checksum(checksum) == self.get(checksum.field_name)
                 for checksum in self._checksums.values()
             )
@@ -1090,6 +1099,7 @@ def __update_simplified_mapping(self, field: Optional[Field] = None) -> None:
             self._simplified_mapping[field.name_length] = field.typeval.size
             self._simplified_mapping[field.name_first] = field.first
             self._simplified_mapping[field.name_last] = field.last
+            self._simplified_mapping[self.message_last_name] = field.last
             return
 
         self._simplified_mapping = {}
@@ -1108,7 +1118,7 @@ def __update_simplified_mapping(self, field: Optional[Field] = None) -> None:
 
         pre_final = self._prev_field("Final")
         if pre_final and self._fields[pre_final].set:
-            self._simplified_mapping[Last("Message")] = self._fields[pre_final].last
+            self._simplified_mapping[self.message_last_name] = self._fields[pre_final].last
 
     def __simplified(self, expr: Expr) -> Expr:
         if expr in {TRUE, FALSE}:
@@ -1216,3 +1226,4 @@ class State:
         fields: Optional[Mapping[str, "MessageValue.Field"]] = None
         checksums: Optional[Mapping[str, "MessageValue.Checksum"]] = None
         type_literals: Optional[Mapping[Name, Expr]] = None
+        last_name: Last = Last("Message")

tests/test_pyrflx.py

@@ -1663,6 +1663,7 @@ def test_no_verification_icmp(icmp: MessageValue) -> None:
     icmp_unv.set("Sequence_Number", 1)
     icmp_unv.set("Data", b"\x00")
     assert icmp_unv.bytestring == icmp.bytestring
+    assert icmp_unv.valid_message
 
 
 def test_no_verification_ethernet(frame: MessageValue) -> None:
@@ -1713,3 +1714,49 @@ def test_no_verification_array_nested_messages(
     array_message_unv.set("Bar", foos_unv)
     assert array_message_unv.valid_message
     assert array_message_unv.bytestring == array_message.bytestring
+
+
+def test_no_verification_icmp_checksum(icmp_checksum: MessageValue, icmp_type: Message) -> None:
+    test_data = (
+        b"\x47\xb4\x67\x5e\x00\x00\x00\x00"
+        b"\x4a\xfc\x0d\x00\x00\x00\x00\x00\x10\x11\x12\x13\x14\x15\x16\x17"
+        b"\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f\x20\x21\x22\x23\x24\x25\x26\x27"
+        b"\x28\x29\x2a\x2b\x2c\x2d\x2e\x2f\x30\x31\x32\x33\x34\x35\x36\x37"
+    )
+    icmp_checksum_unv = MessageValue(
+        icmp_type.copy(
+            structure=[
+                Link(l.source, l.target, condition=And(l.condition, ValidChecksum("Checksum")))
+                if l.target == FINAL
+                else l
+                for l in icmp_type.structure
+            ],
+            aspects={
+                ID("Checksum"): {
+                    ID("Checksum"): [
+                        ValueRange(First("Tag"), Sub(First("Checksum"), Number(1))),
+                        Length("Checksum"),
+                        ValueRange(Add(Last("Checksum"), Number(1)), Last("Message")),
+                    ]
+                }
+            },
+        ),
+        skip_verification=True,
+    )
+    icmp_checksum.set_checksum_function({"Checksum": icmp_checksum_function})
+    icmp_checksum.set("Tag", "Echo_Request")
+    icmp_checksum.set("Code_Zero", 0)
+    icmp_checksum.set("Identifier", 5)
+    icmp_checksum.set("Sequence_Number", 1)
+    icmp_checksum.set("Data", test_data)
+    icmp_checksum_unv.set_checksum_function({"Checksum": icmp_checksum_function})
+    icmp_checksum_unv.set("Tag", "Echo_Request")
+    icmp_checksum_unv.set("Code_Zero", 0)
+    icmp_checksum_unv.set("Checksum", 0)
+    icmp_checksum_unv.set("Identifier", 5)
+    icmp_checksum_unv.set("Sequence_Number", 1)
+    icmp_checksum_unv.set("Data", test_data)
+    icmp_checksum_unv.update_checksums()
+    assert icmp_checksum_unv.valid_message
+    assert icmp_checksum_unv.get("Checksum") == icmp_checksum.get("Checksum")
+    assert icmp_checksum_unv.bytestring == icmp_checksum.bytestring