Re: [PATCH 11/19] rust/qobject: add from/to JSON bindings for QObject

[Paolo Bonzini <pbonzini@redhat.com>]

On 12/5/25 11:04, Markus Armbruster wrote:
> Paolo Bonzini <pbonzini@redhat.com> writes:
> 
>> These are used by tests.  However it could even be an idea to use
>> serde_json + transcoding and get rid of the C version...
> 
> Tell me more!

QEMU's JSON parser produces a QObject.  To obtain the same effect, we 
can take JSON-string-to-serde deserialization (implemented by 
serde_json) and attach it to serde-to-QObject serialization (the thing 
in patch 5).  That results in a JSON-string-to-QObject function.

Doing it in the other direction (QObject deserializer + JSON-string 
serializer) produces a QObject-to-JSON-string function.

For a little more information see https://serde.rs/transcode.html.

Note however that there is no support for push parsing, therefore this 
would not replace the balanced-parentheses machinery in 
qobject/json-streamer.c, and therefore QMP would still need a minimal lexer.

Grr... I just remembered about interpolation :/ so no, we still need a 
parser for libqmp.c.

Paolo

>> 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/wrapper.h          |  1 +
>>   rust/util/src/qobject/mod.rs | 17 +++++++++++++++++
>>   2 files changed, 18 insertions(+)
>>
>> diff --git a/rust/util/wrapper.h b/rust/util/wrapper.h
>> index 0907dd59142..c88820a5e5b 100644
>> --- a/rust/util/wrapper.h
>> +++ b/rust/util/wrapper.h
>> @@ -37,3 +37,4 @@ typedef enum memory_order {
>>   #include "qobject/qobject.h"
>>   #include "qobject/qlist.h"
>>   #include "qobject/qdict.h"
>> +#include "qobject/qjson.h"
>> diff --git a/rust/util/src/qobject/mod.rs b/rust/util/src/qobject/mod.rs
>> index e896aba5f3a..292a3c9c238 100644
>> --- a/rust/util/src/qobject/mod.rs
>> +++ b/rust/util/src/qobject/mod.rs
>> @@ -23,6 +23,7 @@
>>   use common::assert_field_type;
>>   pub use deserializer::from_qobject;
>>   pub use error::{Error, Result};
>> +use foreign::prelude::*;
>>   pub use serializer::to_qobject;
>>   
>>   use crate::bindings;
>> @@ -111,6 +112,22 @@ fn refcnt(&self) -> &AtomicUsize {
>>           let qobj = self.0.get();
>>           unsafe { AtomicUsize::from_ptr(addr_of_mut!((*qobj).base.refcnt)) }
>>       }
>> +
>> +    pub fn to_json(&self) -> String {
>> +        let qobj = self.0.get();
>> +        unsafe {
>> +            let json = bindings::qobject_to_json(qobj);
>> +            glib_sys::g_string_free(json, glib_sys::GFALSE).into_native()
>> +        }
>> +    }
>> +
>> +    pub fn from_json(json: &str) -> std::result::Result<Self, crate::Error> {
>> +        let c_json = std::ffi::CString::new(json)?;
>> +        unsafe {
>> +            crate::Error::with_errp(|errp| bindings::qobject_from_json(c_json.as_ptr(), errp))
>> +                .map(|qobj| QObject::from_raw(qobj))
>> +        }
>> +    }
>>   }
>>   
>>   impl From<()> for QObject {
> 
> 
>