bevy/crates/bevy_log/src/android_tracing.rs

use bevy_utils::tracing::{
    field::Field,
    span::{Attributes, Record},
    Event, Id, Level, Subscriber,
};
use std::fmt::{Debug, Write};
use tracing_subscriber::{field::Visit, layer::Context, registry::LookupSpan, Layer};

#[derive(Default)]
pub(crate) struct AndroidLayer;

struct StringRecorder(String, bool);
impl StringRecorder {
    fn new() -> Self {
        StringRecorder(String::new(), false)
    }
}

impl Visit for StringRecorder {
    fn record_debug(&mut self, field: &Field, value: &dyn Debug) {
        if field.name() == "message" {
            if !self.0.is_empty() {
                self.0 = format!("{:?}\n{}", value, self.0)
            } else {
                self.0 = format!("{:?}", value)
            }
        } else {
            if self.1 {
                // following args
                write!(self.0, " ").unwrap();
            } else {
                // first arg
                self.1 = true;
            }
            write!(self.0, "{} = {:?};", field.name(), value).unwrap();
        }
    }
}

impl core::fmt::Display for StringRecorder {
    fn fmt(&self, mut f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        if !self.0.is_empty() {
            write!(&mut f, " {}", self.0)
        } else {
            Ok(())
        }
    }
}

impl core::default::Default for StringRecorder {
    fn default() -> Self {
        StringRecorder::new()
    }
}

impl<S: Subscriber + for<'a> LookupSpan<'a>> Layer<S> for AndroidLayer {
    fn new_span(&self, attrs: &Attributes<'_>, id: &Id, ctx: Context<'_, S>) {
        let mut new_debug_record = StringRecorder::new();
        attrs.record(&mut new_debug_record);

        if let Some(span_ref) = ctx.span(id) {
            span_ref
                .extensions_mut()
                .insert::<StringRecorder>(new_debug_record);
        }
    }

    fn on_record(&self, id: &Id, values: &Record<'_>, ctx: Context<'_, S>) {
        if let Some(span_ref) = ctx.span(id) {
            if let Some(debug_record) = span_ref.extensions_mut().get_mut::<StringRecorder>() {
                values.record(debug_record);
            }
        }
    }

    fn on_event(&self, event: &Event<'_>, _ctx: Context<'_, S>) {
        let mut recorder = StringRecorder::new();
        event.record(&mut recorder);
        let meta = event.metadata();
        let level = meta.level();
        let priority = match *level {
            Level::TRACE => android_log_sys::LogPriority::VERBOSE,
            Level::DEBUG => android_log_sys::LogPriority::DEBUG,
            Level::INFO => android_log_sys::LogPriority::INFO,
            Level::WARN => android_log_sys::LogPriority::WARN,
            Level::ERROR => android_log_sys::LogPriority::ERROR,
        };
        let message = format!("{}\0", recorder);
        let tag = format!("{}\0", meta.name());
        unsafe {
            android_log_sys::__android_log_write(
                priority as android_log_sys::c_int,
                tag.as_ptr() as *const android_log_sys::c_char,
                message.as_ptr() as *const android_log_sys::c_char,
            );
        }
    }
}