feat: add tracing channels for fetch and middleware handlers

build.config.mjs

@@ -12,6 +12,7 @@ export default defineBuildConfig({
         "src/cli.ts",
         "src/static.ts",
         "src/log.ts",
+        "src/tracing.ts",
         ...[
           "deno",
           "bun",

package.json

@@ -17,6 +17,7 @@
     "./cli": "./dist/cli.mjs",
     "./static": "./dist/static.mjs",
     "./log": "./dist/log.mjs",
+    "./tracing": "./dist/tracing.mjs",
     ".": {
       "types": "./dist/types.d.mts",
       "deno": "./dist/adapters/deno.mjs",

src/_middleware.ts

@@ -1,3 +1,4 @@
+import { traceCall } from "./tracing.ts";
 import type {
   Server,
   ServerRequest,
@@ -8,21 +9,45 @@ import type {
 export function wrapFetch(server: Server): ServerHandler {
   const fetchHandler = server.options.fetch;
   const middleware = server.options.middleware || [];
-  return middleware.length === 0
-    ? fetchHandler
-    : (request) => callMiddleware(request, fetchHandler, middleware, 0);
+
+  if (middleware.length === 0) {
+    return (request) =>
+      traceCall("fetch", async () => await fetchHandler(request), {
+        request,
+        server,
+      });
+  }
+
+  return (request) =>
+    callMiddleware(server, request, fetchHandler, middleware, 0);
 }
 
 function callMiddleware(
+  server: Server,
   request: ServerRequest,
   fetchHandler: ServerHandler,
   middleware: ServerMiddleware[],
   index: number,
 ): Response | Promise<Response> {
   if (index === middleware.length) {
-    return fetchHandler(request);
+    return traceCall("fetch", async () => await fetchHandler(request), {
+      request,
+      server,
+    });
   }
-  return middleware[index](request, () =>
-    callMiddleware(request, fetchHandler, middleware, index + 1),
+
+  const currentMiddleware = middleware[index];
+  const next = () =>
+    callMiddleware(server, request, fetchHandler, middleware, index + 1);
+
+  return traceCall(
+    "middleware",
+    async () => await currentMiddleware(request, next),
+    {
+      request,
+      server,
+      index,
+      name: currentMiddleware?.name,
+    },
   );
 }

src/tracing.ts

@@ -0,0 +1,42 @@
+import { tracingChannel, type TracingChannel } from "node:diagnostics_channel";
+import type { Server, ServerRequest } from "./types.ts";
+
+export type TraceDataMap = {
+  fetch: { request: ServerRequest; server: Server };
+  middleware: {
+    request: ServerRequest;
+    server: Server;
+    index: number;
+    name?: string;
+  };
+};
+
+export type TraceChannelName = keyof TraceDataMap;
+
+const channels: Record<
+  TraceChannelName,
+  TracingChannel<unknown, TraceDataMap[TraceChannelName]>
+> = {
+  fetch: tracingChannel("srvx.fetch"),
+  middleware: tracingChannel("srvx.middleware"),
+};
+
+export function traceCall<
+  TChannel extends TraceChannelName,
+  TReturn,
+  TData extends TraceDataMap[TChannel],
+>(
+  channel: TChannel,
+  exec: () => Promise<TReturn>,
+  data: TData,
+): Promise<TReturn> {
+  return channels[channel].tracePromise(exec, data);
+}
+
+export function traceSync<
+  TChannel extends TraceChannelName,
+  TReturn,
+  TData extends TraceDataMap[TChannel],
+>(channel: TChannel, exec: () => TReturn, data: TData): TReturn {
+  return channels[channel].traceSync(exec, data);
+}