feat: wrap route handlers with tracing at build time

src/build/virtual/routing.ts

@@ -15,10 +15,12 @@ export default function routing(nitro: Nitro) {
         "_importHash"
       );
 
+      const traceH3 = !!nitro.options.tracingChannel?.h3;
+
       return /* js */ `
 import * as __routeRules__ from "#nitro/runtime/route-rules";
 import * as srvxNode from "srvx/node"
-import * as h3 from "h3";
+import * as h3 from "h3";${traceH3 ? `\nimport { wrapHandlerWithTracing } from "h3/tracing";` : ""}
 
 export const findRouteRules = ${nitro.routing.routeRules.compileToString({ serialize: serializeRouteRule, matchAll: true })}
 
@@ -41,7 +43,7 @@ ${allHandlers
   )
   .join("\n")}
 
-export const findRoute = ${nitro.routing.routes.compileToString({ serialize: serializeHandler })}
+export const findRoute = ${nitro.routing.routes.compileToString({ serialize: (h) => serializeHandler(h, { tracing: traceH3 }) })}
 
 export const findRoutedMiddleware = ${nitro.routing.routedMiddleware.compileToString({ serialize: serializeHandler, matchAll: true })};
 
@@ -61,18 +63,20 @@ function uniqueBy<T>(arr: T[], key: keyof T): T[] {
 
 type MaybeArray<T> = T | T[];
 
-function serializeHandler(h: MaybeArray<NitroEventHandler & { _importHash: string }>): string {
+function serializeHandler(
+  h: MaybeArray<NitroEventHandler & { _importHash: string }>,
+  opts: { tracing?: boolean } = {}
+): string {
   const meta = Array.isArray(h) ? h[0] : h;
+  const handler = Array.isArray(h)
+    ? `multiHandler(${h.map((handler) => serializeHandlerFn(handler)).join(",")})`
+    : serializeHandlerFn(h);
 
   return `{${[
     `route:${JSON.stringify(meta.route)}`,
     meta.method && `method:${JSON.stringify(meta.method)}`,
     meta.meta && `meta:${JSON.stringify(meta.meta)}`,
-    `handler:${
-      Array.isArray(h)
-        ? `multiHandler(${h.map((handler) => serializeHandlerFn(handler)).join(",")})`
-        : serializeHandlerFn(h)
-    }`,
+    `handler:${opts.tracing ? `wrapHandlerWithTracing(${handler})` : handler}`,
   ]
     .filter(Boolean)
     .join(",")}}`;

test/unit/virtual-routing.test.ts

@@ -0,0 +1,56 @@
+import { describe, expect, it } from "vitest";
+import type { Nitro, NitroEventHandler } from "nitro/types";
+
+import routing from "../../src/build/virtual/routing.ts";
+
+function createNitroStub(tracingChannel: Nitro["options"]["tracingChannel"]): Nitro {
+  const handler: NitroEventHandler & { _importHash: string } = {
+    route: "/foo",
+    method: "GET",
+    handler: "/path/to/handler.ts",
+    _importHash: "_abc123",
+  };
+
+  return {
+    options: {
+      tracingChannel,
+    },
+    routing: {
+      routes: {
+        routes: [{ route: "/foo", method: "GET", data: handler }],
+        compileToString: ({ serialize }: { serialize: (h: unknown) => string }) =>
+          `{"/foo":${serialize(handler)}}`,
+      },
+      routedMiddleware: {
+        routes: [],
+        compileToString: () => `{}`,
+      },
+      globalMiddleware: [],
+      routeRules: {
+        compileToString: () => `() => []`,
+      },
+    },
+  } as unknown as Nitro;
+}
+
+describe("virtual/routing template", () => {
+  it("does not wrap route handlers when tracingChannel is disabled", () => {
+    const template = routing(createNitroStub(undefined)).template();
+    expect(template).not.toContain("h3/tracing");
+    expect(template).not.toContain("wrapHandlerWithTracing");
+  });
+
+  it("does not wrap route handlers when tracingChannel.h3 is false", () => {
+    const template = routing(
+      createNitroStub({ srvx: true, h3: false, unstorage: true })
+    ).template();
+    expect(template).not.toContain("h3/tracing");
+    expect(template).not.toContain("wrapHandlerWithTracing");
+  });
+
+  it("wraps route handlers with wrapHandlerWithTracing when tracingChannel.h3 is true", () => {
+    const template = routing(createNitroStub({ srvx: true, h3: true, unstorage: true })).template();
+    expect(template).toContain(`import { wrapHandlerWithTracing } from "h3/tracing"`);
+    expect(template).toContain("wrapHandlerWithTracing(h3.toEventHandler(_abc123))");
+  });
+});