Allow manipulating the generator in Duplex.from()

lib/internal/streams/duplexify.js

@@ -83,15 +83,19 @@ module.exports = function duplexify(body, name) {
   }
 
   if (typeof body === 'function') {
-    const { value, write, final, destroy } = fromAsyncGen(body);
+    let d;
+
+    const { value, write, final, destroy } = fromAsyncGen(body, () => {
+      destroyer(d);
+    });
 
     // Body might be a constructor function instead of an async generator function.
     if (isDuplexNodeStream(value)) {
-      return value;
+      return d = value;
     }
 
     if (isIterable(value)) {
-      return from(Duplexify, value, {
+      return d = from(Duplexify, value, {
         // TODO (ronag): highWaterMark?
         objectMode: true,
         write,
@@ -102,12 +106,16 @@ module.exports = function duplexify(body, name) {
 
     const then = value?.then;
     if (typeof then === 'function') {
-      let d;
+      let finalized = false;
 
       const promise = FunctionPrototypeCall(
         then,
         value,
         (val) => {
+          // The function returned without (fully) consuming the generator.
+          if (!finalized) {
+            destroyer(d);
+          }
           if (val != null) {
             throw new ERR_INVALID_RETURN_VALUE('nully', 'body', val);
           }
@@ -123,6 +131,7 @@ module.exports = function duplexify(body, name) {
         readable: false,
         write,
         final(cb) {
+          finalized = true;
           final(async () => {
             try {
               await promise;
@@ -208,11 +217,12 @@ module.exports = function duplexify(body, name) {
     body);
 };
 
-function fromAsyncGen(fn) {
+function fromAsyncGen(fn, destructor) {
   let { promise, resolve } = createDeferredPromise();
   const ac = new AbortController();
   const signal = ac.signal;
-  const value = fn(async function*() {
+
+  const asyncGenerator = (async function* () {
     while (true) {
       const _promise = promise;
       promise = null;
@@ -222,9 +232,47 @@ function fromAsyncGen(fn) {
       if (signal.aborted)
         throw new AbortError(undefined, { cause: signal.reason });
       ({ promise, resolve } = createDeferredPromise());
+      // Next line will "break" the loop if the generator is returned/thrown.
       yield chunk;
     }
-  }(), { signal });
+  })();
+
+  const originalReturn = asyncGenerator.return;
+  asyncGenerator.return = async function(value) {
+    try {
+      return await originalReturn.call(this, value);
+    } finally {
+      if (promise) {
+        const _promise = promise;
+        promise = null;
+        const { cb } = await _promise;
+        process.nextTick(cb);
+
+        destructor();
+      }
+    }
+  };
+
+  const originalThrow = asyncGenerator.throw;
+  asyncGenerator.throw = async function(err) {
+    try {
+      return await originalThrow.call(this, err);
+    } catch (error) {
+      err ??= error;
+      throw error;
+    } finally {
+      if (promise) {
+        const _promise = promise;
+        promise = null;
+        const { cb } = await _promise;
+
+        // asyncGenerator.throw(undefined) should cause a callback error
+        process.nextTick(cb, err ?? new AbortError());
+      }
+    }
+  };
+
+  const value = fn(asyncGenerator, { signal });
 
   return {
     value,

test/parallel/test-stream-duplex-from.js

@@ -5,6 +5,7 @@ const assert = require('assert');
 const { Duplex, Readable, Writable, pipeline, PassThrough } = require('stream');
 const { ReadableStream, WritableStream } = require('stream/web');
 const { Blob } = require('buffer');
+const sleep = require('util').promisify(setTimeout);
 
 {
   const d = Duplex.from({
@@ -401,3 +402,136 @@ function makeATestWritableStream(writeFunc) {
     assert.strictEqual(d.writable, false);
   }));
 }
+
+{
+  const r = Readable.from(['foo', 'bar', 'baz']);
+  pipeline(
+    r,
+    Duplex.from(async function(asyncGenerator) {
+      const values = await Array.fromAsync(asyncGenerator);
+      assert.deepStrictEqual(values, ['foo', 'bar', 'baz']);
+
+      await asyncGenerator.return();
+      await asyncGenerator.return();
+      await asyncGenerator.return();
+    }),
+    common.mustSucceed(() => {
+      assert.strictEqual(r.destroyed, true);
+    })
+  );
+}
+
+{
+  const r = Readable.from(['foo', 'bar', 'baz']);
+  pipeline(
+    r,
+    Duplex.from(async function(asyncGenerator) {
+      // eslint-disable-next-line no-unused-vars
+      for await (const _ of asyncGenerator) break;
+    }),
+    common.mustSucceed(() => {
+      assert.strictEqual(r.destroyed, true);
+    })
+  );
+}
+
+{
+  const r = Readable.from(['foo', 'bar', 'baz']);
+  pipeline(
+    r,
+    Duplex.from(async function(asyncGenerator) {
+      const a = await asyncGenerator.next();
+      assert.strictEqual(a.done, false);
+      assert.strictEqual(a.value.toString(), 'foo');
+      const b = await asyncGenerator.return();
+      assert.strictEqual(b.done, true);
+    }),
+    common.mustSucceed(() => {
+      assert.strictEqual(r.destroyed, true);
+    })
+  );
+}
+
+{
+  const r = Readable.from(['foo', 'bar', 'baz']);
+  pipeline(
+    r,
+    Duplex.from(async function(asyncGenerator) {
+      // Note: the generator is not even started at this point
+      await asyncGenerator.return();
+    }),
+    common.mustSucceed(() => {
+      assert.strictEqual(r.destroyed, true);
+    })
+  );
+}
+
+{
+  const r = Readable.from(['foo', 'bar', 'baz']);
+  pipeline(
+    r,
+    Duplex.from(async function(asyncGenerator) {
+      // Same as before, with a delay
+      await sleep(100);
+      await asyncGenerator.return();
+    }),
+    common.mustSucceed(() => {
+      assert.strictEqual(r.destroyed, true);
+    })
+  );
+}
+
+{
+  const r = Readable.from(['foo', 'bar', 'baz']);
+  pipeline(
+    r,
+    Duplex.from(async function(asyncGenerator) {}),
+    common.mustCall((err) => {
+      assert.strictEqual(err.code, 'ERR_STREAM_PREMATURE_CLOSE');
+      assert.strictEqual(r.destroyed, true);
+    })
+  );
+}
+
+{
+  const r = Readable.from(['foo', 'bar', 'baz']);
+  pipeline(
+    r,
+    Duplex.from(async function(asyncGenerator) {
+      await sleep(100);
+    }),
+    common.mustCall((err) => {
+      assert.strictEqual(err.code, 'ERR_STREAM_PREMATURE_CLOSE');
+      assert.strictEqual(r.destroyed, true);
+    })
+  );
+}
+
+{
+  const r = Readable.from(['foo']);
+  pipeline(
+    r,
+    Duplex.from(async function(asyncGenerator) {
+      await asyncGenerator.throw(new Error('my error'));
+    }),
+    common.mustCall((err) => {
+      assert.strictEqual(err.message, 'my error');
+      assert.strictEqual(r.destroyed, true);
+    })
+  );
+}
+
+{
+  const r = Readable.from(['foo', 'bar']);
+  pipeline(
+    r,
+    Duplex.from(async function(asyncGenerator) {
+      await asyncGenerator.next();
+      await asyncGenerator.throw(new Error('my error'));
+    }),
+    common.mustCall((err) => {
+      assert.strictEqual(err.message, 'my error');
+      assert.strictEqual(r.destroyed, true);
+    })
+  );
+}