[PATCH 05/14] rust: add Serializer (to_qobject) implementation for QObject

[Paolo Bonzini <pbonzini@redhat.com>]

This allows creating QObject from any serializable data structure.

Co-authored-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 rust/util/meson.build               |   2 +
 rust/util/src/qobject/error.rs      |  52 +++
 rust/util/src/qobject/mod.rs        |   4 +
 rust/util/src/qobject/serializer.rs | 585 ++++++++++++++++++++++++++++
 4 files changed, 643 insertions(+)
 create mode 100644 rust/util/src/qobject/error.rs
 create mode 100644 rust/util/src/qobject/serializer.rs

diff --git a/rust/util/meson.build b/rust/util/meson.build
index 5b99d38c903..fb152766003 100644
--- a/rust/util/meson.build
+++ b/rust/util/meson.build
@@ -39,6 +39,8 @@ _util_rs = static_library(
     {'.': _util_bindings_inc_rs,
     'qobject': [
       'src/qobject/mod.rs',
+      'src/qobject/error.rs',
+      'src/qobject/serializer.rs',
       'src/qobject/serialize.rs',
     ]}),
   override_options: ['rust_std=2021', 'build.rust_std=2021'],
diff --git a/rust/util/src/qobject/error.rs b/rust/util/src/qobject/error.rs
new file mode 100644
index 00000000000..5212e65c4f7
--- /dev/null
+++ b/rust/util/src/qobject/error.rs
@@ -0,0 +1,52 @@
+//! Error data type for `QObject`'s `serde` integration
+
+use std::{
+    ffi::NulError,
+    fmt::{self, Display},
+    str::Utf8Error,
+};
+
+use serde::ser;
+
+#[derive(Debug)]
+pub enum Error {
+    Custom(String),
+    KeyMustBeAString,
+    InvalidUtf8,
+    NulEncountered,
+    NumberOutOfRange,
+}
+
+impl ser::Error for Error {
+    fn custom<T: Display>(msg: T) -> Self {
+        Error::Custom(msg.to_string())
+    }
+}
+
+impl From<NulError> for Error {
+    fn from(_: NulError) -> Self {
+        Error::NulEncountered
+    }
+}
+
+impl From<Utf8Error> for Error {
+    fn from(_: Utf8Error) -> Self {
+        Error::InvalidUtf8
+    }
+}
+
+impl Display for Error {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Error::Custom(msg) => formatter.write_str(msg),
+            Error::KeyMustBeAString => formatter.write_str("key must be a string"),
+            Error::InvalidUtf8 => formatter.write_str("invalid UTF-8 in string"),
+            Error::NulEncountered => formatter.write_str("NUL character in string"),
+            Error::NumberOutOfRange => formatter.write_str("number out of range"),
+        }
+    }
+}
+
+impl std::error::Error for Error {}
+
+pub type Result<T> = std::result::Result<T, Error>;
diff --git a/rust/util/src/qobject/mod.rs b/rust/util/src/qobject/mod.rs
index 2e3cb247b27..cd034185748 100644
--- a/rust/util/src/qobject/mod.rs
+++ b/rust/util/src/qobject/mod.rs
@@ -6,7 +6,9 @@
 
 #![deny(clippy::unwrap_used)]
 
+mod error;
 mod serialize;
+mod serializer;
 
 use std::{
     cell::UnsafeCell,
@@ -17,6 +19,8 @@
 };
 
 use common::assert_field_type;
+pub use error::{Error, Result};
+pub use serializer::to_qobject;
 
 use crate::bindings;
 
diff --git a/rust/util/src/qobject/serializer.rs b/rust/util/src/qobject/serializer.rs
new file mode 100644
index 00000000000..59200683f5d
--- /dev/null
+++ b/rust/util/src/qobject/serializer.rs
@@ -0,0 +1,585 @@
+//! `QObject` serializer
+//!
+//! This module implements a [`Serializer`](serde::ser::Serializer) that
+//! produces `QObject`s, allowing them to be created from serializable data
+//! structures (such as primitive data types, or structs that implement
+//! `Serialize`).
+
+use std::ffi::CString;
+
+use serde::ser::{Impossible, Serialize};
+
+use super::{
+    error::{Error, Result},
+    QObject,
+};
+
+pub struct SerializeTupleVariant {
+    name: CString,
+    vec: Vec<QObject>,
+}
+
+impl serde::ser::SerializeTupleVariant for SerializeTupleVariant {
+    type Ok = QObject;
+    type Error = Error;
+
+    fn serialize_field<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        self.vec.push(to_qobject(value)?);
+        Ok(())
+    }
+
+    fn end(self) -> Result<QObject> {
+        let SerializeTupleVariant { name, vec, .. } = self;
+
+        // TODO: insert elements one at a time
+        let list = QObject::from_iter(vec);
+
+        // serde by default represents enums as a single-entry object, with
+        // the variant stored in the key ("external tagging").  Internal tagging
+        // is implemented by the struct that requests it, not by the serializer.
+        let map = [(name, list)];
+        Ok(QObject::from_iter(map))
+    }
+}
+
+pub struct SerializeStructVariant {
+    name: CString,
+    vec: Vec<(CString, QObject)>,
+}
+
+impl serde::ser::SerializeStructVariant for SerializeStructVariant {
+    type Ok = QObject;
+    type Error = Error;
+
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        self.vec.push((CString::new(key)?, to_qobject(value)?));
+        Ok(())
+    }
+
+    fn end(self) -> Result<QObject> {
+        // TODO: insert keys one at a time
+        let SerializeStructVariant { name, vec, .. } = self;
+        let list = QObject::from_iter(vec);
+
+        // serde by default represents enums as a single-entry object, with
+        // the variant stored in the key ("external tagging").  Internal tagging
+        // is implemented by the struct that requests it, not by the serializer.
+        let map = [(name, list)];
+        Ok(QObject::from_iter(map))
+    }
+}
+
+pub struct SerializeVec {
+    vec: Vec<QObject>,
+}
+
+impl serde::ser::SerializeSeq for SerializeVec {
+    type Ok = QObject;
+    type Error = Error;
+
+    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        self.vec.push(to_qobject(value)?);
+        Ok(())
+    }
+
+    fn end(self) -> Result<QObject> {
+        // TODO: insert elements one at a time
+        let SerializeVec { vec, .. } = self;
+        let list = QObject::from_iter(vec);
+        Ok(list)
+    }
+}
+
+impl serde::ser::SerializeTuple for SerializeVec {
+    type Ok = QObject;
+    type Error = Error;
+
+    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        serde::ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    fn end(self) -> Result<QObject> {
+        serde::ser::SerializeSeq::end(self)
+    }
+}
+
+impl serde::ser::SerializeTupleStruct for SerializeVec {
+    type Ok = QObject;
+    type Error = Error;
+
+    fn serialize_field<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        serde::ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    fn end(self) -> Result<QObject> {
+        serde::ser::SerializeSeq::end(self)
+    }
+}
+
+struct MapKeySerializer;
+
+impl serde::Serializer for MapKeySerializer {
+    type Ok = CString;
+    type Error = Error;
+
+    type SerializeSeq = Impossible<CString, Error>;
+    type SerializeTuple = Impossible<CString, Error>;
+    type SerializeTupleStruct = Impossible<CString, Error>;
+    type SerializeTupleVariant = Impossible<CString, Error>;
+    type SerializeMap = Impossible<CString, Error>;
+    type SerializeStruct = Impossible<CString, Error>;
+    type SerializeStructVariant = Impossible<CString, Error>;
+
+    #[inline]
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+    ) -> Result<CString> {
+        Ok(CString::new(variant)?)
+    }
+
+    #[inline]
+    fn serialize_newtype_struct<T>(self, _name: &'static str, value: &T) -> Result<CString>
+    where
+        T: ?Sized + Serialize,
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_bool(self, _value: bool) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_i8(self, _value: i8) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_i16(self, _value: i16) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_i32(self, _value: i32) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_i64(self, _value: i64) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_i128(self, _value: i128) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_u8(self, _value: u8) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_u16(self, _value: u16) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_u32(self, _value: u32) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_u64(self, _value: u64) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_u128(self, _value: u128) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_f32(self, _value: f32) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_f64(self, _value: f64) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    #[inline]
+    fn serialize_char(self, _value: char) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    #[inline]
+    fn serialize_str(self, value: &str) -> Result<CString> {
+        Ok(CString::new(value)?)
+    }
+
+    fn serialize_bytes(self, value: &[u8]) -> Result<CString> {
+        Ok(CString::new(value)?)
+    }
+
+    fn serialize_unit(self) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_newtype_variant<T>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _value: &T,
+    ) -> Result<CString>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_none(self) -> Result<CString> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_some<T>(self, _value: &T) -> Result<CString>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleStruct> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleVariant> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_struct(self, _name: &'static str, _len: usize) -> Result<Self::SerializeStruct> {
+        Err(Error::KeyMustBeAString)
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant> {
+        Err(Error::KeyMustBeAString)
+    }
+}
+
+pub struct SerializeMap {
+    vec: Vec<(CString, QObject)>,
+    next_key: Option<CString>,
+}
+
+impl serde::ser::SerializeMap for SerializeMap {
+    type Ok = QObject;
+    type Error = Error;
+
+    fn serialize_key<T>(&mut self, key: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        self.next_key = Some(key.serialize(MapKeySerializer)?);
+        Ok(())
+    }
+
+    fn serialize_value<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        let key = self.next_key.take();
+        // Panic because this indicates a bug in the program rather than an
+        // expected failure.
+        let key = key.expect("serialize_value called before serialize_key");
+        self.vec.push((key, to_qobject(value)?));
+        Ok(())
+    }
+
+    fn end(self) -> Result<QObject> {
+        // TODO: insert keys one at a time
+        let SerializeMap { vec, .. } = self;
+        Ok(QObject::from_iter(vec))
+    }
+}
+
+impl serde::ser::SerializeStruct for SerializeMap {
+    type Ok = QObject;
+    type Error = Error;
+
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        serde::ser::SerializeMap::serialize_entry(self, key, value)
+    }
+
+    fn end(self) -> Result<QObject> {
+        serde::ser::SerializeMap::end(self)
+    }
+}
+
+/// Serializer whose output is a `QObject`.
+///
+/// This is the serializer that backs [`to_qobject`].
+pub struct Serializer;
+
+impl serde::Serializer for Serializer {
+    type Ok = QObject;
+    type Error = Error;
+    type SerializeSeq = SerializeVec;
+    type SerializeTuple = SerializeVec;
+    type SerializeTupleStruct = SerializeVec;
+    type SerializeTupleVariant = SerializeTupleVariant;
+    type SerializeMap = SerializeMap;
+    type SerializeStruct = SerializeMap;
+    type SerializeStructVariant = SerializeStructVariant;
+
+    #[inline]
+    fn serialize_bool(self, value: bool) -> Result<QObject> {
+        Ok(value.into())
+    }
+
+    #[inline]
+    fn serialize_i8(self, value: i8) -> Result<QObject> {
+        self.serialize_i64(i64::from(value))
+    }
+
+    #[inline]
+    fn serialize_i16(self, value: i16) -> Result<QObject> {
+        self.serialize_i64(i64::from(value))
+    }
+
+    #[inline]
+    fn serialize_i32(self, value: i32) -> Result<QObject> {
+        self.serialize_i64(i64::from(value))
+    }
+
+    fn serialize_i64(self, value: i64) -> Result<QObject> {
+        Ok(value.into())
+    }
+
+    fn serialize_i128(self, value: i128) -> Result<QObject> {
+        if let Ok(value) = u64::try_from(value) {
+            Ok(value.into())
+        } else if let Ok(value) = i64::try_from(value) {
+            Ok(value.into())
+        } else {
+            Err(Error::NumberOutOfRange)
+        }
+    }
+
+    #[inline]
+    fn serialize_u8(self, value: u8) -> Result<QObject> {
+        self.serialize_u64(u64::from(value))
+    }
+
+    #[inline]
+    fn serialize_u16(self, value: u16) -> Result<QObject> {
+        self.serialize_u64(u64::from(value))
+    }
+
+    #[inline]
+    fn serialize_u32(self, value: u32) -> Result<QObject> {
+        self.serialize_u64(u64::from(value))
+    }
+
+    #[inline]
+    fn serialize_u64(self, value: u64) -> Result<QObject> {
+        Ok(value.into())
+    }
+
+    fn serialize_u128(self, value: u128) -> Result<QObject> {
+        if let Ok(value) = u64::try_from(value) {
+            Ok(value.into())
+        } else {
+            Err(Error::NumberOutOfRange)
+        }
+    }
+
+    #[inline]
+    fn serialize_f32(self, float: f32) -> Result<QObject> {
+        self.serialize_f64(f64::from(float))
+    }
+
+    #[inline]
+    fn serialize_f64(self, float: f64) -> Result<QObject> {
+        Ok(float.into())
+    }
+
+    #[inline]
+    fn serialize_char(self, value: char) -> Result<QObject> {
+        let mut s = String::new();
+        s.push(value);
+        Ok(CString::new(s)?.into())
+    }
+
+    #[inline]
+    fn serialize_str(self, value: &str) -> Result<QObject> {
+        Ok(CString::new(value)?.into())
+    }
+
+    fn serialize_bytes(self, value: &[u8]) -> Result<QObject> {
+        // Serialize into a vector of numeric QObjects
+        let it = value.iter().map(|&b| u64::from(b));
+        Ok(QObject::from_iter(it))
+    }
+
+    #[inline]
+    fn serialize_unit(self) -> Result<QObject> {
+        Ok(().into())
+    }
+
+    #[inline]
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<QObject> {
+        self.serialize_unit()
+    }
+
+    #[inline]
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+    ) -> Result<QObject> {
+        self.serialize_str(variant)
+    }
+
+    #[inline]
+    fn serialize_newtype_struct<T>(self, _name: &'static str, value: &T) -> Result<QObject>
+    where
+        T: ?Sized + Serialize,
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_newtype_variant<T>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        value: &T,
+    ) -> Result<QObject>
+    where
+        T: ?Sized + Serialize,
+    {
+        // serde by default represents enums as a single-entry object, with
+        // the variant stored in the key ("external tagging").  Internal tagging
+        // is implemented by the struct that requests it, not by the serializer.
+        let map = [(CString::new(variant)?, to_qobject(value)?)];
+        Ok(QObject::from_iter(map))
+    }
+
+    #[inline]
+    fn serialize_none(self) -> Result<QObject> {
+        self.serialize_unit()
+    }
+
+    #[inline]
+    fn serialize_some<T>(self, value: &T) -> Result<QObject>
+    where
+        T: ?Sized + Serialize,
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_seq(self, len: Option<usize>) -> Result<Self::SerializeSeq> {
+        Ok(SerializeVec {
+            vec: Vec::with_capacity(len.unwrap_or(0)),
+        })
+    }
+
+    fn serialize_tuple(self, len: usize) -> Result<Self::SerializeTuple> {
+        self.serialize_seq(Some(len))
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeTupleStruct> {
+        self.serialize_seq(Some(len))
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeTupleVariant> {
+        Ok(SerializeTupleVariant {
+            name: CString::new(variant)?,
+            vec: Vec::with_capacity(len),
+        })
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
+        Ok(SerializeMap {
+            vec: Vec::new(),
+            next_key: None,
+        })
+    }
+    fn serialize_struct(self, _name: &'static str, len: usize) -> Result<Self::SerializeStruct> {
+        self.serialize_map(Some(len))
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant> {
+        Ok(SerializeStructVariant {
+            name: CString::new(variant)?,
+            vec: Vec::new(),
+        })
+    }
+}
+
+pub fn to_qobject<T>(input: T) -> Result<QObject>
+where
+    T: Serialize,
+{
+    input.serialize(Serializer)
+}
-- 
2.51.0