fix(blocks): attribute values are validated before any write; null/bool/objects refused by tag

block_insert and block_set_attributes applied str() to whatever arrived, so
a JSON null became the text None and a non-mapping failed after the INSERT
was written. validate_attribute_values (backends/block_specs.py) runs first
on both engines: strings pass the one-line rule, ints and finite floats are
written as plain digits, everything else is a TypeError naming the tag.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

backends/block_specs.py

@@ -204,6 +204,38 @@ def validate_attdef_specs(attdefs) -> list[dict]:
     return out
 
 
+def validate_attribute_values(attributes, where: str = "attributes") -> dict[str, str]:
+    """``{TAG: value}`` for ``block_insert`` / ``block_set_attributes`` as the
+    strings that will be written, refused before any write.
+
+    ``str(value)`` used to be applied to whatever arrived, so a JSON ``null``
+    became the text ``None``, ``true`` became ``True`` and an object became its
+    Python repr — silently, on both engines. A string is taken as is (one line,
+    the DXF rule ``_one_line`` enforces); an int or a finite float is written
+    with ``str`` (``101`` → ``"101"``, ``2.5`` → ``"2.5"``); ``bool``, ``None``,
+    lists and objects are refused by tag. ``None`` for the whole mapping means
+    "no attributes".
+    """
+    if attributes is None:
+        return {}
+    if not isinstance(attributes, dict):
+        raise TypeError(f"{where} must be an object of {{TAG: value}} pairs")
+    out: dict[str, str] = {}
+    for tag, value in attributes.items():
+        if not isinstance(tag, str) or not tag.strip():
+            raise TypeError(f"{where}: every tag must be a non-empty string")
+        label = f"{where}[{tag!r}]"
+        if isinstance(value, str):
+            out[tag] = _one_line(value, label)
+        elif isinstance(value, bool) or value is None or not isinstance(value, (int, float)):
+            raise TypeError(f"{label} must be a string or a number, got {type(value).__name__}")
+        else:
+            if isinstance(value, float) and not math.isfinite(value):
+                raise TypeError(f"{label} must be finite")
+            out[tag] = str(value)
+    return out
+
+
 def solid_vertices(points: list[tuple[float, float]]) -> list[tuple[float, float]]:
     """DXF SOLID draws vtx0→vtx1→vtx3→vtx2, so a quad given in polygon order
     (a, b, c, d) is stored as (a, b, d, c). Triangles are stored as given."""

backends/com_backend.py

@@ -3315,6 +3315,10 @@ class ComBackend(AutoCADBackend):
         attributes=None,
         layer=None,
     ) -> EntityInfo:
+        from backends.block_specs import validate_attribute_values
+
+        values = validate_attribute_values(attributes)
+
         def _sync():
             _require_block_defined(_acad_doc(), name)
             mspace = _msp()
@@ -3328,13 +3332,13 @@ class ComBackend(AutoCADBackend):
             )
             if layer:
                 ref.Layer = layer
-            if attributes:
+            if values:
                 try:
                     attrs = ref.GetAttributes()
                     for attr in attrs:
                         tag = attr.TagString
-                        if tag in attributes:
-                            attr.TextString = str(attributes[tag])
+                        if tag in values:
+                            attr.TextString = values[tag]
                 except Exception as exc:
                     log.debug("Block insert: GetAttributes or attribute setting failed: %s", exc)
             return _entity_info(ref)
@@ -3730,6 +3734,10 @@ class ComBackend(AutoCADBackend):
         return await self._run(_sync)
 
     async def block_set_attributes(self, handle, attributes) -> dict:
+        from backends.block_specs import validate_attribute_values
+
+        values = validate_attribute_values(attributes)
+
         def _sync():
             doc = _acad_doc()
             ref = doc.HandleToObject(handle)
@@ -3737,8 +3745,8 @@ class ComBackend(AutoCADBackend):
             updated = []
             for attr in attrs:
                 tag = attr.TagString
-                if tag in attributes:
-                    attr.TextString = str(attributes[tag])
+                if tag in values:
+                    attr.TextString = values[tag]
                     updated.append(tag)
             return {"ok": True, "updated_tags": updated}
 

backends/ezdxf_backend.py

@@ -4520,6 +4520,10 @@ class EzdxfBackend(AutoCADBackend):
         attributes=None,
         layer=None,
     ) -> EntityInfo:
+        from backends.block_specs import validate_attribute_values
+
+        values = validate_attribute_values(attributes)
+
         def _sync():
             msp = self._msp()
             attribs: dict = {
@@ -4531,12 +4535,12 @@ class EzdxfBackend(AutoCADBackend):
                 attribs["layer"] = layer
             self._require_block(name)
             ref = msp.add_blockref(name, (float(x), float(y)), dxfattribs=attribs)
-            if attributes:
+            if values:
                 # `add_auto_blockref` wraps the INSERT in an anonymous *U block,
                 # so the returned handle names `*U1` and carries no ATTRIBs.
                 # `add_auto_attribs` attaches ATTRIBs to this INSERT for every
                 # ATTDEF the definition has; values for tags it lacks are ignored.
-                ref.add_auto_attribs({str(k): str(v) for k, v in attributes.items()})
+                ref.add_auto_attribs(values)
             self._mark_dirty()
             return _entity_info_dxf(ref)
 
@@ -4828,6 +4832,10 @@ class EzdxfBackend(AutoCADBackend):
         return await self._async(_sync)
 
     async def block_set_attributes(self, handle, attributes) -> dict:
+        from backends.block_specs import validate_attribute_values
+
+        values = validate_attribute_values(attributes)
+
         def _sync():
             ent = self._get_entity(handle)
             if ent.dxftype() != "INSERT":
@@ -4835,8 +4843,8 @@ class EzdxfBackend(AutoCADBackend):
             updated = []
             for attrib in ent.attribs:
                 tag = attrib.dxf.tag
-                if tag in attributes:
-                    self._write_attrib_value(attrib, str(attributes[tag]))
+                if tag in values:
+                    self._write_attrib_value(attrib, values[tag])
                     updated.append(tag)
             self._mark_dirty()
             return {"ok": True, "updated_tags": updated}

server.py

@@ -3011,7 +3011,15 @@ async def block_insert(
     layer: Annotated[str | None, "Layer name"] = None,
     ctx: Context = None,
 ) -> dict:
-    """Insert a block and optionally set attribute values."""
+    """Insert a block and optionally set attribute values.
+
+    Refused before any write, on both engines: an undefined or layout block
+    name, and an attribute value that is not text — a string is written as
+    is (one line), an int or finite float as its plain digits (`101` →
+    `"101"`), while `null`, booleans, lists and objects are refused naming
+    the tag (they used to be written as their Python repr). Values for tags
+    the block does not define are ignored.
+    """
     await ctx.info(f"Inserting block '{name}' at ({x},{y})")
     result = await _backend(ctx).block_insert(
         name, x, y, scale_x, scale_y, rotation, attributes, layer
@@ -3085,6 +3093,11 @@ async def block_set_attributes(
 ) -> dict:
     """Update attribute values in a block reference.
 
+    Same value rule as `block_insert`: strings and numbers are written,
+    `null` / booleans / lists / objects are refused naming the tag before
+    anything changes. `updated_tags` lists the tags that exist on the
+    reference and were written; unknown tags are ignored.
+
     A multi-line attribute takes `Line1\\PLine2` and keeps every line; the
     value written is the one `block_get_attributes` reads back and
     `block_explode` bursts, on both engines.

tests/test_track_a_hardening.py

@@ -1504,3 +1504,88 @@ async def test_com_explode_undoes_a_burst_that_fails_after_explode(com):
     assert placeholder.deleted is True
     assert [t.deleted for t in sheet.texts] == [True], "the TEXT written before the failure"
     assert space.calls == []
+
+
+# ── Task 3: attribute values are validated before any write ──────────────────
+
+
+@pytest.mark.parametrize(
+    "value, fragment",
+    [
+        (None, "NoneType"),
+        (True, "bool"),
+        ({"a": 1}, "dict"),
+        ([1, 2], "list"),
+        (float("nan"), "finite"),
+        ("two\nlines", "single line"),
+    ],
+)
+async def test_insert_refuses_a_non_text_attribute_value_by_tag(backend, value, fragment):
+    _define_tagged_block(backend)
+    before = len(list(backend._msp()))
+    with pytest.raises(TypeError, match=r"attributes\['TAG'\]") as exc:
+        await backend.block_insert("TB", 0, 0, attributes={"TAG": value})
+    assert fragment in str(exc.value)
+    assert len(list(backend._msp())) == before, "a refused insert must not write"
+
+
+async def test_insert_refuses_a_non_mapping_before_writing(backend):
+    _define_tagged_block(backend)
+    before = len(list(backend._msp()))
+    with pytest.raises(TypeError, match="attributes must be an object"):
+        await backend.block_insert("TB", 0, 0, attributes=[("TAG", "x")])
+    assert len(list(backend._msp())) == before
+
+
+async def test_insert_writes_numbers_as_plain_text(backend):
+    _define_tagged_block(backend)
+    ref = await backend.block_insert("TB", 0, 0, attributes={"TAG": 101})
+    assert await backend.block_get_attributes(ref.handle) == {"TAG": "101"}
+    ref = await backend.block_insert("TB", 0, 0, attributes={"TAG": 2.5})
+    assert await backend.block_get_attributes(ref.handle) == {"TAG": "2.5"}
+
+
+async def test_set_attributes_refuses_by_tag_and_leaves_the_value_alone(backend):
+    _define_tagged_block(backend)
+    ref = await backend.block_insert("TB", 0, 0, attributes={"TAG": "P-101"})
+    with pytest.raises(TypeError, match=r"attributes\['TAG'\] must be a string or a number"):
+        await backend.block_set_attributes(ref.handle, {"TAG": None})
+    assert await backend.block_get_attributes(ref.handle) == {"TAG": "P-101"}
+    result = await backend.block_set_attributes(ref.handle, {"TAG": 7})
+    assert result == {"ok": True, "updated_tags": ["TAG"]}
+    assert await backend.block_get_attributes(ref.handle) == {"TAG": "7"}
+
+
+async def test_com_insert_refuses_before_insert_block_and_writes_numbers_as_text(com):
+    backend, document, space = com
+    space.attributes = {"TAG": ""}
+    with pytest.raises(TypeError, match=r"attributes\['TAG'\]"):
+        await backend.block_insert("TB", 0, 0, attributes={"TAG": None})
+    assert space.calls == [], "the refusal fires before InsertBlock"
+
+    await backend.block_insert("TB", 0, 0, attributes={"TAG": 101})
+    assert [name for name, _ in space.calls] == ["InsertBlock"]
+    attr = space.inserted[0].GetAttributes()[0]
+    assert attr.TextString == "101" and ("TextString", "101") in attr.writes
+
+
+async def test_com_set_attributes_refuses_before_touching_the_reference(com):
+    backend, document, space = com
+    attr = _FakeObject("AcDbAttribute", "A1", TagString="TAG", TextString="P-101")
+    calls = []
+
+    def get_attributes():
+        calls.append("GetAttributes")
+        return (attr,)
+
+    document.objects["2F"] = _FakeObject(
+        "AcDbBlockReference", "2F", Name="TB", GetAttributes=get_attributes
+    )
+    with pytest.raises(TypeError, match=r"attributes\['TAG'\]"):
+        await backend.block_set_attributes("2F", {"TAG": True})
+    assert calls == [] and attr.TextString == "P-101"
+    assert await backend.block_set_attributes("2F", {"TAG": 2.5}) == {
+        "ok": True,
+        "updated_tags": ["TAG"],
+    }
+    assert attr.TextString == "2.5"