Make tracing-aka-logging example more realistic (#1869)

examples/tracing-aka-logging/src/main.rs

@@ -6,6 +6,7 @@
 
 use axum::{
     body::Bytes,
+    extract::MatchedPath,
     http::{HeaderMap, Request},
     response::{Html, Response},
     routing::get,
@@ -13,7 +14,7 @@ use axum::{
 };
 use std::{net::SocketAddr, time::Duration};
 use tower_http::{classify::ServerErrorsFailureClass, trace::TraceLayer};
-use tracing::Span;
+use tracing::{info_span, Span};
 use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};
 
 #[tokio::main]
@@ -33,20 +34,35 @@ async fn main() {
         // It provides good defaults but is also very customizable.
         //
         // See https://docs.rs/tower-http/0.1.1/tower_http/trace/index.html for more details.
-        .layer(TraceLayer::new_for_http())
-        // If you want to customize the behavior using closures here is how
         //
-        // This is just for demonstration, you don't need to add this middleware twice
+        // If you want to customize the behavior using closures here is how.
         .layer(
             TraceLayer::new_for_http()
+                .make_span_with(|request: &Request<_>| {
+                    // Log the matched route's path (with placeholders not filled in).
+                    // Use request.uri() or OriginalUri if you want the real path.
+                    let matched_path = request
+                        .extensions()
+                        .get::<MatchedPath>()
+                        .map(MatchedPath::as_str);
+
+                    info_span!(
+                        "http_request",
+                        method = ?request.method(),
+                        matched_path,
+                        some_other_field = tracing::field::Empty,
+                    )
+                })
                 .on_request(|_request: &Request<_>, _span: &Span| {
-                    // ...
+                    // You can use `_span.record("some_other_field", value)` in one of these
+                    // closures to attach a value to the initially empty field in the info_span
+                    // created above.
                 })
                 .on_response(|_response: &Response, _latency: Duration, _span: &Span| {
                     // ...
                 })
                 .on_body_chunk(|_chunk: &Bytes, _latency: Duration, _span: &Span| {
-                    // ..
+                    // ...
                 })
                 .on_eos(
                     |_trailers: Option<&HeaderMap>, _stream_duration: Duration, _span: &Span| {