Fix potential frame parsing issue where an empty payload is still valid

Author: puddly

tests/test_commands.py

@@ -531,3 +531,22 @@ def test_command_replace_partial():
 
     assert command1.replace() == command1
     assert command1.replace(SysId=0x13) == command2
+
+
+def test_command_possibly_empty_payload():
+    class TestSubsystem(t.CommandsBase, subsystem=t.Subsystem.SYS):
+        Test = t.CommandDef(
+            t.CommandType.AREQ,
+            0x00,
+            rsp_schema=(t.Param("Data", t.Bytes, "Can be any length"),),
+        )
+
+    Test = TestSubsystem.Test.Callback
+
+    assert Test.from_frame(
+        frames.GeneralFrame(header=Test.header, data=b"test")
+    ) == Test(Data=t.Bytes(b"test"))
+
+    assert Test.from_frame(frames.GeneralFrame(header=Test.header, data=b"")) == Test(
+        Data=t.Bytes(b"")
+    )

zigpy_znp/types/commands.py

@@ -407,16 +407,21 @@ def from_frame(cls, frame, *, ignore_unparsed=False) -> "CommandBase":
         params = {}
 
         for param in cls.schema:
-            if data:
+            try:
                 params[param.name], data = param.type.deserialize(data)
-            elif not param.optional:
-                # If we're out of data but the parameter is required, this is bad
-                raise ValueError(
-                    f"Data has been consumed but required parameters remain: {param}"
-                )
-            else:
-                # If we're out of data and the parameter is optional, we're done
-                break
+            except ValueError:
+                if not data and param.optional:
+                    # If we're out of data and the parameter is optional, we're done
+                    break
+                elif not data and not param.optional:
+                    # If we're out of data but the parameter is required, this is bad
+                    raise ValueError(
+                        f"Frame data is truncated (parsed {params}),"
+                        f" required parameter remains: {param}"
+                    )
+                else:
+                    # Otherwise, let the exception happen
+                    raise
 
         if data:
             msg = (