aptu_coder/
logging.rs

1// SPDX-FileCopyrightText: 2026 aptu-coder contributors
2// SPDX-License-Identifier: Apache-2.0
3//! MCP logging integration via tracing.
4//!
5//! Provides a custom tracing subscriber that forwards log events to MCP clients.
6
7use serde_json::{Map, Value};
8use std::sync::{Arc, Mutex};
9use tokio::sync::mpsc;
10use tracing::subscriber::Interest;
11use tracing::{Level, Subscriber};
12use tracing_subscriber::Layer;
13use tracing_subscriber::filter::LevelFilter;
14use tracing_subscriber::layer::Context;
15
16/// Lightweight event sent from `McpLoggingLayer` to consumer task via unbounded channel.
17#[derive(Clone, Debug)]
18pub struct LogEvent {
19    pub level: Level,
20    pub logger: String,
21    pub data: Value,
22}
23
24/// Custom tracing Layer that bridges tracing events to `MCP` client via unbounded channel.
25/// Sends lightweight [`LogEvent`] to channel; consumer task in `on_initialized` drains with `recv_many`.
26pub struct McpLoggingLayer {
27    event_tx: mpsc::UnboundedSender<LogEvent>,
28    log_level_filter: Arc<Mutex<LevelFilter>>,
29}
30
31impl McpLoggingLayer {
32    pub fn new(
33        event_tx: mpsc::UnboundedSender<LogEvent>,
34        log_level_filter: Arc<Mutex<LevelFilter>>,
35    ) -> Self {
36        Self {
37            event_tx,
38            log_level_filter,
39        }
40    }
41}
42
43impl<S> Layer<S> for McpLoggingLayer
44where
45    S: Subscriber,
46{
47    fn on_event(&self, event: &tracing::Event<'_>, _ctx: Context<'_, S>) {
48        let metadata = event.metadata();
49        let level = *metadata.level();
50        let target = metadata.target();
51
52        // Check if event level passes the current filter before processing
53        let filter_level = self
54            .log_level_filter
55            .lock()
56            .unwrap_or_else(std::sync::PoisonError::into_inner);
57        if level > *filter_level {
58            return;
59        }
60        drop(filter_level);
61
62        // Extract fields from the event using a visitor that collects into a Map.
63        let mut fields = Map::new();
64        let mut visitor = MessageVisitor(&mut fields);
65        event.record(&mut visitor);
66
67        let logger = target.to_string();
68        let data = Value::Object(fields);
69
70        // Send LogEvent to channel without blocking on_event.
71        let log_event = LogEvent {
72            level,
73            logger,
74            data,
75        };
76
77        // Ignore send error if receiver is dropped (channel closed).
78        let _ = self.event_tx.send(log_event);
79    }
80
81    fn register_callsite(&self, metadata: &'static tracing::Metadata<'static>) -> Interest {
82        let filter_level = self
83            .log_level_filter
84            .lock()
85            .unwrap_or_else(std::sync::PoisonError::into_inner);
86        if *metadata.level() <= *filter_level {
87            Interest::always()
88        } else {
89            Interest::never()
90        }
91    }
92
93    fn enabled(&self, metadata: &tracing::Metadata<'_>, _ctx: Context<'_, S>) -> bool {
94        let filter_level = self
95            .log_level_filter
96            .lock()
97            .unwrap_or_else(std::sync::PoisonError::into_inner);
98        *metadata.level() <= *filter_level
99    }
100}
101
102/// Visitor to extract fields from tracing event into a JSON Map.
103struct MessageVisitor<'a>(&'a mut Map<String, Value>);
104
105impl tracing::field::Visit for MessageVisitor<'_> {
106    fn record_debug(&mut self, field: &tracing::field::Field, value: &dyn std::fmt::Debug) {
107        self.0.insert(
108            field.name().to_string(),
109            Value::String(format!("{value:?}")),
110        );
111    }
112
113    fn record_str(&mut self, field: &tracing::field::Field, value: &str) {
114        self.0
115            .insert(field.name().to_string(), Value::String(value.to_string()));
116    }
117
118    fn record_u64(&mut self, field: &tracing::field::Field, value: u64) {
119        self.0
120            .insert(field.name().to_string(), Value::Number(value.into()));
121    }
122
123    fn record_i64(&mut self, field: &tracing::field::Field, value: i64) {
124        self.0
125            .insert(field.name().to_string(), Value::Number(value.into()));
126    }
127
128    fn record_bool(&mut self, field: &tracing::field::Field, value: bool) {
129        self.0.insert(field.name().to_string(), Value::Bool(value));
130    }
131}
132
133#[cfg(test)]
134mod tests {
135    use super::*;
136    use tracing::Level;
137    #[test]
138    fn test_log_event_level_is_tracing_level() {
139        let event = LogEvent {
140            level: Level::ERROR,
141            logger: "test".to_string(),
142            data: Value::Null,
143        };
144        assert_eq!(event.level, Level::ERROR);
145    }
146}
aptu_coder/logging.rs

aptu_coder/
logging.rs
