Validate TextIOWrapper chunk size

shAn-kor · shAn-kor · commit dcd75ef495ff · 2026-07-13T00:25:45.000+09:00
Match CPython for non-positive, oversized, and index-compatible values.

Assisted-by: Codex:GPT-5
diff --git a/crates/vm/src/stdlib/_io.rs b/crates/vm/src/stdlib/_io.rs
@@ -3206,19 +3206,27 @@ mod _io {
         }
 
         #[pygetset(setter, name = "_CHUNK_SIZE")]
-        fn set_chunksize(
-            &self,
-            chunk_size: PySetterValue<usize>,
-            vm: &VirtualMachine,
-        ) -> PyResult<()> {
-            let mut textio = self.lock(vm)?;
-            match chunk_size {
-                PySetterValue::Assign(chunk_size) => textio.chunk_size = chunk_size,
+        fn set_chunksize(&self, value: PySetterValue, vm: &VirtualMachine) -> PyResult<()> {
+            let chunk_size: isize = match value {
+                PySetterValue::Assign(object_value) => {
+                    let integer = object_value.try_index(vm)?;
+
+                    integer.try_to_primitive::<isize>(vm).map_err(|_| {
+                        vm.new_value_error("cannot fit 'int' into an index-sized integer")
+                    })?
+                }
                 PySetterValue::Delete => Err(vm.new_attribute_error("cannot delete attribute"))?,
             };
-            // TODO: RUSTPYTHON
-            // Change chunk_size type, validate it manually and throws ValueError if invalid.
-            // https://github.com/python/cpython/blob/2e9da8e3522764d09f1d6054a2be567e91a30812/Modules/_io/textio.c#L3124-L3143
+
+            if chunk_size <= 0 {
+                return Err(vm.new_value_error("a strictly positive integer is required"));
+            }
+
+            let chunk_size = usize::try_from(chunk_size)
+                .map_err(|_| vm.new_value_error("a strictly positive integer is required"))?;
+
+            let mut textio = self.lock(vm)?;
+            textio.chunk_size = chunk_size;
             Ok(())
         }
 
diff --git a/extra_tests/snippets/stdlib_io.py b/extra_tests/snippets/stdlib_io.py
@@ -84,3 +84,30 @@ def write(self, data):
 raw.textio = textio
 with assert_raises(AttributeError):
     textio.writelines(["x"])
+
+textio = TextIOWrapper(BytesIO())
+
+for invalid_chunk_size in (0, -1, 2**100):
+    try:
+        textio._CHUNK_SIZE = invalid_chunk_size
+    except ValueError:
+        pass
+    else:
+        assert False, f"expected ValueError for {invalid_chunk_size!r}"
+
+for invalid_chunk_size in (1.5, "4"):
+    try:
+        textio._CHUNK_SIZE = invalid_chunk_size
+    except TypeError:
+        pass
+    else:
+        assert False, f"expected TypeError for {invalid_chunk_size!r}"
+
+
+class ChunkSize:
+    def __index__(self):
+        return 16
+
+
+textio._CHUNK_SIZE = ChunkSize()
+assert textio._CHUNK_SIZE == 16
