1 files changed, 80 insertions, 0 deletions
diff --git a/js/trace.ts b/js/trace.ts
new file mode 100644
index 000000000..42a9fe015
--- /dev/null
+++ b/js/trace.ts
@@ -0,0 +1,80 @@
+// Copyright 2018 the Deno authors. All rights reserved. MIT license.
+import * as fbs from "gen/msg_generated";
+
+export interface TraceInfo {
+  sync: boolean; // is synchronous call
+  name: string; // name of operation
+}
+
+interface TraceStackNode {
+  list: TraceInfo[];
+  prev: TraceStackNode | null;
+}
+
+let current: TraceStackNode | null = null;
+
+// Push a new list to trace stack
+function pushStack(): void {
+  if (current === null) {
+    current = { list: [], prev: null };
+  } else {
+    const newStack = { list: [], prev: current };
+    current = newStack;
+  }
+}
+
+// Pop from trace stack and (if possible) concat to parent trace stack node
+function popStack(): TraceInfo[] {
+  if (current === null) {
+    throw new Error("trace list stack should not be empty");
+  }
+  const resultList = current!.list;
+  if (!!current!.prev) {
+    const prev = current!.prev!;
+    // concat inner results to outer stack
+    prev.list = prev.list.concat(resultList);
+    current = prev;
+  } else {
+    current = null;
+  }
+  return resultList;
+}
+
+// Push to trace stack if we are tracing
+export function maybePushTrace(op: fbs.Any, sync: boolean): void {
+  if (current === null) {
+    return; // no trace requested
+  }
+  // Freeze the object, avoid tampering
+  current!.list.push(
+    Object.freeze({
+      sync,
+      name: fbs.Any[op] // convert to enum names
+    })
+  );
+}
+
+/**
+ * Trace operations executed inside a given function or promise.
+ * Notice: To capture every operation in asynchronous deno.* calls,
+ * you might want to put them in functions instead of directly invoking.
+ *
+ *     import { trace, mkdir } from "deno";
+ *
+ *     const ops = await trace(async () => {
+ *       await mkdir("my_dir");
+ *     });
+ *     // ops becomes [{ sync: false, name: "Mkdir" }]
+ */
+export async function trace(
+  // tslint:disable-next-line:no-any
+  fnOrPromise: Function | Promise<any>
+): Promise<TraceInfo[]> {
+  pushStack();
+  if (typeof fnOrPromise === "function") {
+    await fnOrPromise();
+  } else {
+    await fnOrPromise;
+  }
+  return popStack();
+}