[PATCH v2 05/16] rust/qobject: add Deserialize implementation

Paolo Bonzini
2026-01-08T13:13:03Z

This allows QObject to be created from any serializable format, for
example JSON via serde_json.

This is not too useful, since QObjects are produced by
C code or by serializing structs, but it can be used for testing
and it is part of the full implementation of a serde format.

It is relatively simple and similar to the Serializer, just with
the extra indirection of a Visitor.

Co-authored-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
rust/util/meson.build | 1 +
rust/util/src/qobject/deserialize.rs | 134 +++++++++++++++++++++++++++
rust/util/src/qobject/mod.rs | 1 +
3 files changed, 136 insertions(+)
create mode 100644 rust/util/src/qobject/deserialize.rs

diff --git a/rust/util/meson.build b/rust/util/meson.build
index 7829364c09a..4621932fdcb 100644
--- a/rust/util/meson.build
+++ b/rust/util/meson.build
@@ -40,6 +40,7 @@ _util_rs = static_library(
{'.': _util_bindings_inc_rs,
'qobject': [
'src/qobject/mod.rs',
+ 'src/qobject/deserialize.rs',
'src/qobject/error.rs',
'src/qobject/serializer.rs',
'src/qobject/serialize.rs',
diff --git a/rust/util/src/qobject/deserialize.rs b/rust/util/src/qobject/deserialize.rs
new file mode 100644
index 00000000000..280a577b6be
--- /dev/null
+++ b/rust/util/src/qobject/deserialize.rs
@@ -0,0 +1,134 @@
+//! `QObject` deserialization
+//!
+//! This module implements the [`Deserialize`] trait for `QObject`,
+//! allowing it to be created from any serializable format, for
+//! example JSON.
+
+use core::fmt;
+use std::ffi::CString;
+
+use serde::de::{self, Deserialize, MapAccess, SeqAccess, Visitor};
+
+use super::{to_qobject, QObject};
+
+impl<'de> Deserialize<'de> for QObject {
+ #[inline]
+ fn deserialize<D>(deserializer: D) -> Result<QObject, D::Error>
+ where
+ D: serde::Deserializer<'de>,
+ {
+ struct ValueVisitor;
+
+ impl<'de> Visitor<'de> for ValueVisitor {
+ type Value = QObject;
+
+ fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+ formatter.write_str("any valid JSON value")
+ }
+
+ #[inline]
+ fn visit_bool<E>(self, value: bool) -> Result<QObject, E> {
+ Ok(value.into())
+ }
+
+ #[inline]
+ fn visit_i64<E>(self, value: i64) -> Result<QObject, E> {
+ Ok(value.into())
+ }
+
+ fn visit_i128<E>(self, value: i128) -> Result<QObject, E>
+ where
+ E: serde::de::Error,
+ {
+ to_qobject(value).map_err(|_| de::Error::custom("number out of range"))
+ }
+
+ #[inline]
+ fn visit_u64<E>(self, value: u64) -> Result<QObject, E> {
+ Ok(value.into())
+ }
+
+ fn visit_u128<E>(self, value: u128) -> Result<QObject, E>
+ where
+ E: serde::de::Error,
+ {
+ to_qobject(value).map_err(|_| de::Error::custom("number out of range"))
+ }
+
+ #[inline]
+ fn visit_f64<E>(self, value: f64) -> Result<QObject, E> {
+ Ok(value.into())
+ }
+
+ #[inline]
+ fn visit_str<E>(self, value: &str) -> Result<QObject, E>
+ where
+ E: serde::de::Error,
+ {
+ CString::new(value)
+ .map_err(|_| de::Error::custom("NUL character in string"))
+ .map(QObject::from)
+ }
+
+ #[inline]
+ fn visit_string<E>(self, value: String) -> Result<QObject, E>
+ where
+ E: serde::de::Error,
+ {
+ CString::new(value)
+ .map_err(|_| de::Error::custom("NUL character in string"))
+ .map(QObject::from)
+ }
+
+ #[inline]
+ fn visit_none<E>(self) -> Result<QObject, E> {
+ Ok(().into())
+ }
+
+ #[inline]
+ fn visit_some<D>(self, deserializer: D) -> Result<QObject, D::Error>
+ where
+ D: serde::Deserializer<'de>,
+ {
+ Deserialize::deserialize(deserializer)
+ }
+
+ #[inline]
+ fn visit_unit<E>(self) -> Result<QObject, E> {
+ Ok(().into())
+ }
+
+ #[inline]
+ fn visit_seq<V>(self, mut visitor: V) -> Result<QObject, V::Error>
+ where
+ V: SeqAccess<'de>,
+ {
+ // TODO: insert elements one at a time
+ let mut vec = Vec::<QObject>::new();
+
+ while let Some(elem) = visitor.next_element()? {
+ vec.push(elem);
+ }
+ Ok(QObject::from_iter(vec))
+ }
+
+ fn visit_map<V>(self, mut visitor: V) -> Result<QObject, V::Error>
+ where
+ V: MapAccess<'de>,
+ {
+ // TODO: insert elements one at a time
+ let mut vec = Vec::<(CString, QObject)>::new();
+
+ if let Some(first_key) = visitor.next_key()? {
+ vec.push((first_key, visitor.next_value()?));
+ while let Some((key, value)) = visitor.next_entry()? {
+ vec.push((key, value));
+ }
+ }
+ Ok(QObject::from_iter(vec))
+ }
+ }
+
+ deserializer.deserialize_any(ValueVisitor)
+ }
+}
diff --git a/rust/util/src/qobject/mod.rs b/rust/util/src/qobject/mod.rs
index bfa3e9e34bb..c0c16f28049 100644
--- a/rust/util/src/qobject/mod.rs
+++ b/rust/util/src/qobject/mod.rs
@@ -6,6 +6,7 @@

#![deny(clippy::unwrap_used)]

+mod deserialize;
mod error;
mod serialize;
mod serializer;
--
2.52.0