tracing: allow &[u8] to be recorded as event/span field

tracing-core/src/field.rs

@@ -224,6 +224,11 @@ pub trait Visit {
         self.record_debug(field, &value)
     }
 
+    /// Visit a byte slice.
+    fn record_byte_slice(&mut self, field: &Field, value: &[u8]) {
+        self.record_debug(field, &value)
+    }
+
     /// Records a type implementing `Error`.
     ///
     /// <div class="example-wrap" style="display:inline-block">
@@ -443,6 +448,14 @@ impl Value for str {
     }
 }
 
+impl crate::sealed::Sealed for [u8] {}
+
+impl Value for [u8] {
+    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
+        visitor.record_byte_slice(key, self)
+    }
+}
+
 #[cfg(feature = "std")]
 impl crate::sealed::Sealed for dyn std::error::Error + 'static {}
 

tracing-subscriber/src/fmt/format/json.rs

@@ -488,6 +488,11 @@ impl<'a> field::Visit for JsonVisitor<'a> {
             .insert(field.name(), serde_json::Value::from(value));
     }
 
+    fn record_byte_slice(&mut self, field: &Field, value: &[u8]) {
+        self.values
+            .insert(field.name(), serde_json::Value::from(value));
+    }
+
     fn record_debug(&mut self, field: &Field, value: &dyn fmt::Debug) {
         match field.name() {
             // Skip fields that are actually log metadata that have already been handled
@@ -528,13 +533,13 @@ mod test {
     #[test]
     fn json() {
         let expected =
-        "{\"timestamp\":\"fake time\",\"level\":\"INFO\",\"span\":{\"answer\":42,\"name\":\"json_span\",\"number\":3},\"spans\":[{\"answer\":42,\"name\":\"json_span\",\"number\":3}],\"target\":\"tracing_subscriber::fmt::format::json::test\",\"fields\":{\"message\":\"some json test\"}}\n";
+        "{\"timestamp\":\"fake time\",\"level\":\"INFO\",\"span\":{\"answer\":42,\"name\":\"json_span\",\"number\":3,\"slice\":[97,98,99]},\"spans\":[{\"answer\":42,\"name\":\"json_span\",\"number\":3,\"slice\":[97,98,99]}],\"target\":\"tracing_subscriber::fmt::format::json::test\",\"fields\":{\"message\":\"some json test\"}}\n";
         let collector = collector()
             .flatten_event(false)
             .with_current_span(true)
             .with_span_list(true);
         test_json(expected, collector, || {
-            let span = tracing::span!(tracing::Level::INFO, "json_span", answer = 42, number = 3);
+            let span = tracing::span!(tracing::Level::INFO, "json_span", answer = 42, number = 3, slice = &b"abc"[..]);
             let _guard = span.enter();
             tracing::info!("some json test");
         });

tracing-subscriber/src/fmt/format/pretty.rs

@@ -426,6 +426,17 @@ impl<'a> PrettyVisitor<'a> {
 }
 
 impl<'a> field::Visit for PrettyVisitor<'a> {
+    fn record_byte_slice(&mut self, field: &Field, value: &[u8]) {
+        let hex =
+            value
+                .iter()
+                .fold(String::with_capacity(value.len() * 2), |mut acc, byte| {
+                    acc.push_str(&format!("{byte:02x}"));
+                    acc
+                });
+        self.record_debug(field, &format_args!("{}", hex));
+    }
+
     fn record_str(&mut self, field: &Field, value: &str) {
         if self.result.is_err() {
             return;