codex-rs/core/src/utils/json.rs

#[derive(Default)]
struct JsonByteCounter(usize);

impl std::io::Write for JsonByteCounter {
    fn write(&mut self, bytes: &[u8]) -> std::io::Result<usize> {
        self.0 = self.0.saturating_add(bytes.len());
        Ok(bytes.len())
    }

    fn flush(&mut self) -> std::io::Result<()> {
        Ok(())
    }
}

/// Counts serialized JSON bytes without retaining the serialized output.
pub(crate) fn serialized_json_bytes<T: serde::Serialize + ?Sized>(
    value: &T,
) -> serde_json::Result<usize> {
    let mut counter = JsonByteCounter::default();
    serde_json::to_writer(&mut counter, value)?;
    Ok(counter.0)
}