feat: metric for method not found

Author: prestwich

src/metrics.rs

@@ -33,6 +33,11 @@ pub(crate) const ROUTER_PARSE_ERRORS: &str = "ajj.router.parse_errors";
 pub(crate) const ROUTER_PARSE_ERRORS_HELP: &str =
     "Number of parse errors encountered by ajj router methods. This implies no response was sent.";
 
+/// Metric for counting method not found errors.
+pub(crate) const ROUTER_METHOD_NOT_FOUND: &str = "ajj.router.method_not_found";
+pub(crate) const ROUTER_METHOD_NOT_FOUND_HELP: &str =
+    "Number of times ajj router methods encountered a method not found error. This implies a response was sent.";
+
 static DESCRIBE: LazyLock<()> = LazyLock::new(|| {
     metrics::describe_counter!(ROUTER_CALLS, metrics::Unit::Count, ROUTER_CALLS_HELP);
     metrics::describe_counter!(ROUTER_ERRORS, metrics::Unit::Count, ROUTER_ERRORS_HELP);
@@ -56,6 +61,11 @@ static DESCRIBE: LazyLock<()> = LazyLock::new(|| {
         metrics::Unit::Count,
         ROUTER_PARSE_ERRORS_HELP
     );
+    metrics::describe_counter!(
+        ROUTER_METHOD_NOT_FOUND,
+        metrics::Unit::Count,
+        ROUTER_METHOD_NOT_FOUND_HELP
+    );
 });
 
 /// Get or register a counter for calls to a specific service and method.
@@ -168,3 +178,20 @@ pub(crate) fn record_parse_error(service_name: &'static str) {
     let counter = parse_errors(service_name);
     counter.increment(1);
 }
+
+/// Get or register a counter for method not found errors.
+pub(crate) fn method_not_found_errors(service_name: &'static str, method: &str) -> Counter {
+    let _ = &DESCRIBE;
+    metrics::counter!(ROUTER_METHOD_NOT_FOUND, "service" => service_name.to_string(), "method" => method.to_string())
+}
+
+/// Record a method not found error.
+pub(crate) fn record_method_not_found(
+    response_sent: bool,
+    service_name: &'static str,
+    method: &str,
+) {
+    let counter = method_not_found_errors(service_name, method);
+    counter.increment(1);
+    record_output(response_sent, service_name, method);
+}

src/routes/ctx.rs

@@ -464,8 +464,18 @@ impl HandlerArgs {
         self.req.id_owned()
     }
 
+    /// Get the method of the JSON-RPC request.
+    pub fn method(&self) -> &str {
+        self.req.method()
+    }
+
     /// Get the OpenTelemetry span name for this handler invocation.
     pub fn otel_span_name(&self) -> String {
         format!("{}/{}", self.ctx.service_name(), self.req.method())
     }
+
+    /// Get the service name for this handler invocation.
+    pub const fn service_name(&self) -> &'static str {
+        self.ctx.service_name()
+    }
 }

src/routes/mod.rs

@@ -52,8 +52,12 @@ impl Route {
     pub(crate) fn default_fallback() -> Self {
         Self::new(tower::service_fn(|args: HandlerArgs| async {
             let id = args.id_owned();
+            crate::metrics::record_method_not_found(
+                id.is_some(),
+                args.service_name(),
+                args.method(),
+            );
             drop(args); // no longer needed
-
             Ok(Response::maybe_method_not_found(id.as_deref()))
         }))
     }