fix: FastraceEvent should not hardcode layout

src/append/fastrace.rs

@@ -16,6 +16,7 @@ use jiff::Zoned;
 use log::Record;
 
 use crate::append::Append;
+use crate::layout::collect_kvs;
 use crate::layout::KvDisplay;
 
 /// An appender that adds log records to fastrace as an event associated to the current span.
@@ -24,14 +25,11 @@ pub struct FastraceEvent;
 
 impl Append for FastraceEvent {
     fn append(&self, record: &Record) -> anyhow::Result<()> {
-        let message = format!(
-            "{} {:>5} {}{}",
-            Zoned::now(),
-            record.level(),
-            record.args(),
-            KvDisplay::new(record.key_values()),
-        );
-        fastrace::Event::add_to_local_parent(message, || []);
+        let message = format!("{}", record.args(),);
+        fastrace::Event::add_to_local_parent(message, || {
+            [("level", record.level()), ("timestamp", Zoned::now())]
+                .chain(collect_kvs(record.key_values()))
+        });
         Ok(())
     }
 

src/layout/kv.rs

@@ -45,3 +45,25 @@ impl<'a, 'kvs> log::kv::Visitor<'kvs> for KvWriter<'a, 'kvs> {
         Ok(())
     }
 }
+
+/// A helper to collect log's key-value pairs.
+pub fn collect_kvs(kv: &dyn log::kv::Source) -> Vec<(String, String)> {
+    let mut collector = KvCollector { kv: Vec::new() };
+    kv.visit(&mut collector).ok();
+    collector.kv
+}
+
+struct KvCollector {
+    kv: Vec<(String, String)>,
+}
+
+impl<'kvs> log::kv::Visitor<'kvs> for KvCollector {
+    fn visit_pair(
+        &mut self,
+        key: log::kv::Key<'kvs>,
+        value: log::kv::Value<'kvs>,
+    ) -> Result<(), log::kv::Error> {
+        self.kv.push((key.to_string(), value.to_string()));
+        Ok(())
+    }
+}

src/layout/mod.rs

@@ -18,6 +18,7 @@ pub use custom::CustomLayout;
 pub use identical::IdenticalLayout;
 #[cfg(feature = "json")]
 pub use json::JsonLayout;
+pub use kv::collect_kvs;
 pub use kv::KvDisplay;
 pub use text::LevelColor;
 pub use text::TextLayout;