From 05d8cf6600613fb2e9fd334f62fcee69171e181a Mon Sep 17 00:00:00 2001
From: Peter Kolloch <peter.kolloch@nexxiot.com>
Date: Wed, 21 Dec 2022 11:08:32 +0100
Subject: [PATCH] [PathPattern] Record and use PathPattern in response

...so metrics correctly report the innermost PathPattern.

https://github.com/poem-web/poem/issues/461
---
 poem/src/middleware/opentelemetry_metrics.rs | 14 +++++---
 poem/src/route/router.rs                     | 37 ++++++++++++++------
 2 files changed, 37 insertions(+), 14 deletions(-)

diff --git a/poem/src/middleware/opentelemetry_metrics.rs b/poem/src/middleware/opentelemetry_metrics.rs
index 87e4b0642a..1e18f56683 100644
--- a/poem/src/middleware/opentelemetry_metrics.rs
+++ b/poem/src/middleware/opentelemetry_metrics.rs
@@ -79,10 +79,6 @@ impl<E: Endpoint> Endpoint for OpenTelemetryMetricsEndpoint<E> {
         let mut labels = Vec::with_capacity(3);
         labels.push(trace::HTTP_METHOD.string(req.method().to_string()));
         labels.push(trace::HTTP_URL.string(req.original_uri().to_string()));
-        if let Some(path_pattern) = req.data::<PathPattern>() {
-            const HTTP_PATH_PATTERN: Key = Key::from_static_str("http.path_pattern");
-            labels.push(HTTP_PATH_PATTERN.string(path_pattern.0.to_string()));
-        }
 
         let s = Instant::now();
         let res = self.inner.call(req).await.map(IntoResponse::into_response);
@@ -90,9 +86,19 @@ impl<E: Endpoint> Endpoint for OpenTelemetryMetricsEndpoint<E> {
 
         match &res {
             Ok(resp) => {
+                if let Some(path_pattern) = resp.data::<PathPattern>() {
+                    const HTTP_PATH_PATTERN: Key = Key::from_static_str("http.path_pattern");
+                    labels.push(HTTP_PATH_PATTERN.string(path_pattern.0.to_string()));
+                }
+
                 labels.push(trace::HTTP_STATUS_CODE.i64(resp.status().as_u16() as i64));
             }
             Err(err) => {
+                if let Some(path_pattern) = err.data::<PathPattern>() {
+                    const HTTP_PATH_PATTERN: Key = Key::from_static_str("http.path_pattern");
+                    labels.push(HTTP_PATH_PATTERN.string(path_pattern.0.to_string()));
+                }
+
                 labels.push(trace::HTTP_STATUS_CODE.i64(err.status().as_u16() as i64));
                 self.error_count.add(&cx, 1, &labels);
                 labels.push(trace::EXCEPTION_MESSAGE.string(err.to_string()));
diff --git a/poem/src/route/router.rs b/poem/src/route/router.rs
index 0b5747c36e..be03861135 100644
--- a/poem/src/route/router.rs
+++ b/poem/src/route/router.rs
@@ -298,7 +298,7 @@ impl Route {
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 #[allow(unreachable_pub)]
 pub struct PathPattern(pub Arc<str>);
 
@@ -316,17 +316,34 @@ impl Endpoint for Route {
                     None => matches.data.pattern.clone(),
                 };
 
-                match (req.data::<PathPattern>(), req.data::<PathPrefix>()) {
-                    (Some(parent), Some(prefix)) => req.set_data(PathPattern(
-                        format!("{}{}", parent.0, &pattern[prefix.0..]).into(),
-                    )),
-                    (None, Some(prefix)) => req.set_data(PathPattern(pattern[prefix.0..].into())),
-                    (None, None) => req.set_data(PathPattern(pattern)),
-                    (Some(parent), None) => {
-                        req.set_data(PathPattern(format!("{}{}", parent.0, pattern).into()))
+                let pattern = match (req.data::<PathPattern>(), req.data::<PathPrefix>()) {
+                    (Some(parent), Some(prefix)) => {
+                        PathPattern(format!("{}{}", parent.0, &pattern[prefix.0..]).into())
+                    }
+                    (None, Some(prefix)) => PathPattern(pattern[prefix.0..].into()),
+                    (None, None) => PathPattern(pattern),
+                    (Some(parent), None) => PathPattern(format!("{}{}", parent.0, pattern).into()),
+                };
+                req.set_data(pattern.clone());
+
+                let result = matches.data.data.call(req).await;
+
+                // Add PathPattern to the innermost response so that metrics instrumentation
+                // can report the innermost matched pattern.
+                match result {
+                    Ok(mut res) => {
+                        if res.data::<PathPattern>().is_none() {
+                            res.set_data(pattern);
+                        }
+                        Ok(res)
+                    }
+                    Err(mut err) => {
+                        if err.data::<PathPattern>().is_none() {
+                            err.set_data(pattern);
+                        }
+                        Err(err)
                     }
                 }
-                matches.data.data.call(req).await
             }
             None => Err(NotFoundError.into()),
         }