Re: [PATCH 06/19] rust/qobject: add Serialize implementation

[Markus Armbruster <armbru@redhat.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> This allows QObject to be converted to other formats, for example
> JSON via serde_json.
>
> This is not too useful, since QObjects are consumed by
> C code or deserialized into structs, but it can be used for testing
> and it is part of the full implementation of a serde format.
>
> 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/Cargo.lock                    |  1 +
>  rust/util/Cargo.toml               |  1 +
>  rust/util/meson.build              |  3 +-
>  rust/util/src/qobject/mod.rs       |  4 +-
>  rust/util/src/qobject/serialize.rs | 59 ++++++++++++++++++++++++++++++
>  5 files changed, 65 insertions(+), 3 deletions(-)
>  create mode 100644 rust/util/src/qobject/serialize.rs
>
> diff --git a/rust/Cargo.lock b/rust/Cargo.lock
> index 11085133490..7c9f85d5728 100644
> --- a/rust/Cargo.lock
> +++ b/rust/Cargo.lock
> @@ -445,6 +445,7 @@ dependencies = [
>   "foreign",
>   "glib-sys",
>   "libc",
> + "serde",
>  ]
>  
>  [[package]]
> diff --git a/rust/util/Cargo.toml b/rust/util/Cargo.toml
> index 85f91436545..554004816eb 100644
> --- a/rust/util/Cargo.toml
> +++ b/rust/util/Cargo.toml
> @@ -17,6 +17,7 @@ anyhow = { workspace = true }
>  foreign = { workspace = true }
>  glib-sys = { workspace = true }
>  libc = { workspace = true }
> +serde = { workspace = true }
>  common = { path = "../common" }
>  
>  [lints]
> diff --git a/rust/util/meson.build b/rust/util/meson.build
> index ce468ea5227..9fafaf76a37 100644
> --- a/rust/util/meson.build
> +++ b/rust/util/meson.build
> @@ -39,10 +39,11 @@ _util_rs = static_library(
>      {'.': _util_bindings_inc_rs,
>      'qobject': [
>        'src/qobject/mod.rs',
> +      'src/qobject/serialize.rs',
>      ]}),
>    override_options: ['rust_std=2021', 'build.rust_std=2021'],
>    rust_abi: 'rust',
> -  dependencies: [anyhow_rs, libc_rs, foreign_rs, glib_sys_rs, common_rs, qom, qemuutil],
> +  dependencies: [anyhow_rs, libc_rs, foreign_rs, glib_sys_rs, common_rs, serde_rs, qom, qemuutil],
>  )
>  
>  util_rs = declare_dependency(link_with: [_util_rs])
> diff --git a/rust/util/src/qobject/mod.rs b/rust/util/src/qobject/mod.rs
> index 9c6f168d6e1..0913fabc1ee 100644
> --- a/rust/util/src/qobject/mod.rs
> +++ b/rust/util/src/qobject/mod.rs
> @@ -6,6 +6,8 @@
>  
>  #![deny(clippy::unwrap_used)]
>  
> +mod serialize;
> +
>  use std::{
>      cell::UnsafeCell,
>      ffi::{c_char, CString},
> @@ -230,7 +232,6 @@ fn drop(&mut self) {
>      }
>  }
>  
> -#[allow(unused)]
>  macro_rules! match_qobject {
>      (@internal ($qobj:expr) =>
>          $(() => $unit:expr,)?
> @@ -313,5 +314,4 @@ macro_rules! match_qobject {
>                  $($type $(($val))? => $code,)+)
>      };
>  }
> -#[allow(unused_imports)]
>  use match_qobject;
> diff --git a/rust/util/src/qobject/serialize.rs b/rust/util/src/qobject/serialize.rs
> new file mode 100644
> index 00000000000..34ec3847c1d
> --- /dev/null
> +++ b/rust/util/src/qobject/serialize.rs
> @@ -0,0 +1,59 @@
> +//! `QObject` serialization
> +//!
> +//! This module implements the [`Serialize`] trait for `QObject`,
> +//! allowing it to be converted to other formats, for example
> +//! JSON.
> +
> +use std::{ffi::CStr, mem::ManuallyDrop, ptr::addr_of};
> +
> +use serde::ser::{self, Serialize, SerializeMap, SerializeSeq};
> +
> +use super::{match_qobject, QObject};
> +use crate::bindings;
> +
> +impl Serialize for QObject {
> +    #[inline]
> +    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
> +    where
> +        S: ::serde::Serializer,
> +    {
> +        match_qobject! { (self) =>
> +            () => serializer.serialize_unit(),
> +            bool(b) => serializer.serialize_bool(b),
> +            i64(i) => serializer.serialize_i64(i),
> +            u64(u) => serializer.serialize_u64(u),
> +            f64(f) => serializer.serialize_f64(f),
> +            CStr(cstr) => cstr.to_str().map_or_else(
> +                |_| Err(ser::Error::custom("invalid UTF-8 in QString")),

Could this be a programming error?  Like flawed input validation?

> +                |s| serializer.serialize_str(s),
> +            ),
> +            QList(l) => {
> +                let mut node_ptr = unsafe { l.head.tqh_first };
> +                let mut state = serializer.serialize_seq(None)?;
> +                while !node_ptr.is_null() {
> +                    let node = unsafe { &*node_ptr };
> +                    let elem = unsafe { ManuallyDrop::new(QObject::from_raw(addr_of!(*node.value))) };
> +                    state.serialize_element(&*elem)?;
> +                    node_ptr = unsafe { node.next.tqe_next };
> +                }
> +                state.end()
> +            },
> +            QDict(d) => {
> +                let mut state = serializer.serialize_map(Some(d.size))?;
> +                let mut e_ptr = unsafe { bindings::qdict_first(d) };
> +                while !e_ptr.is_null() {
> +                    let e = unsafe { &*e_ptr };
> +                    let key = unsafe { CStr::from_ptr(e.key) };
> +                    key.to_str().map_or_else(
> +                        |_| Err(ser::Error::custom("invalid UTF-8 in key")),
> +                        |k| state.serialize_key(k),
> +                    )?;
> +                    let value = unsafe { ManuallyDrop::new(QObject::from_raw(addr_of!(*e.value))) };
> +                    state.serialize_value(&*value)?;
> +                    e_ptr = unsafe { bindings::qdict_next(d, e) };
> +                }
> +                state.end()
> +            }
> +        }
> +    }
> +}