stream: close iterator in Readable.from

Call iterator.return() if not all of its values are consumed.

Fixes: nodejs#32842

lib/internal/streams/from.js

@@ -34,21 +34,49 @@ function from(Readable, iterable, opts) {
     objectMode: true,
     ...opts
   });
+
   // Reading boolean to protect against _read
   // being called before last iteration completion.
   let reading = false;
+
+  // needToClose boolean if iterator needs to be explicitly closed
+  let needToClose = false;
+
   readable._read = function() {
     if (!reading) {
       reading = true;
       next();
     }
   };
+
+  readable._destroy = function(error, cb) {
+    close().then(
+      () => cb(error),
+      (e) => cb(error || e),
+    );
+  };
+
+  async function close() {
+    if (needToClose) {
+      needToClose = false;
+      if (typeof iterator.return === 'function') {
+        const { value } = await iterator.return();
+        await value;
+      }
+    }
+  }
+
   async function next() {
     try {
+      needToClose = false;
       const { value, done } = await iterator.next();
+      needToClose = !done;
+      const resolved = await value;
       if (done) {
         readable.push(null);
-      } else if (readable.push(await value)) {
+      } else if (readable.destroyed) {
+        await close();
+      } else if (readable.push(resolved)) {
         next();
       } else {
         reading = false;

test/parallel/test-readable-from-iterator-closing.js

@@ -0,0 +1,163 @@
+'use strict';
+
+const { mustCall, mustNotCall } = require('../common');
+const { Readable } = require('stream');
+const { strictEqual } = require('assert');
+
+async function asyncSupport() {
+  const finallyMustCall = mustCall();
+  const bodyMustCall = mustCall();
+
+  async function* infiniteGenerate() {
+    try {
+      while (true) yield 'a';
+    } finally {
+      finallyMustCall();
+    }
+  }
+
+  const stream = Readable.from(infiniteGenerate());
+
+  for await (const chunk of stream) {
+    bodyMustCall();
+    strictEqual(chunk, 'a');
+    break;
+  }
+}
+
+async function syncSupport() {
+  const finallyMustCall = mustCall();
+  const bodyMustCall = mustCall();
+
+  function* infiniteGenerate() {
+    try {
+      while (true) yield 'a';
+    } finally {
+      finallyMustCall();
+    }
+  }
+
+  const stream = Readable.from(infiniteGenerate());
+
+  for await (const chunk of stream) {
+    bodyMustCall();
+    strictEqual(chunk, 'a');
+    break;
+  }
+}
+
+async function syncPromiseSupport() {
+  const returnMustBeAwaited = mustCall();
+  const bodyMustCall = mustCall();
+
+  function* infiniteGenerate() {
+    try {
+      while (true) yield Promise.resolve('a');
+    } finally {
+      // eslint-disable-next-line no-unsafe-finally
+      return { then(cb) {
+        returnMustBeAwaited();
+        cb();
+      } };
+    }
+  }
+
+  const stream = Readable.from(infiniteGenerate());
+
+  for await (const chunk of stream) {
+    bodyMustCall();
+    strictEqual(chunk, 'a');
+    break;
+  }
+}
+
+async function syncRejectedSupport() {
+  const returnMustBeAwaited = mustCall();
+  const bodyMustNotCall = mustNotCall();
+  const catchMustCall = mustCall();
+  const secondNextMustNotCall = mustNotCall();
+
+  function* generate() {
+    try {
+      yield Promise.reject('a');
+      secondNextMustNotCall();
+    } finally {
+      // eslint-disable-next-line no-unsafe-finally
+      return { then(cb) {
+        returnMustBeAwaited();
+        cb();
+      } };
+    }
+  }
+
+  const stream = Readable.from(generate());
+
+  try {
+    for await (const chunk of stream) {
+      bodyMustNotCall(chunk);
+    }
+  } catch {
+    catchMustCall();
+  }
+}
+
+async function noReturnAfterThrow() {
+  const returnMustNotCall = mustNotCall();
+  const bodyMustNotCall = mustNotCall();
+  const catchMustCall = mustCall();
+  const nextMustCall = mustCall();
+
+  const stream = Readable.from({
+    [Symbol.asyncIterator]() { return this; },
+    async next() {
+      nextMustCall();
+      throw new Error('a');
+    },
+    async return() {
+      returnMustNotCall();
+      return { done: true };
+    },
+  });
+
+  try {
+    for await (const chunk of stream) {
+      bodyMustNotCall(chunk);
+    }
+  } catch {
+    catchMustCall();
+  }
+}
+
+async function closeStreamWhileNextIsPending() {
+  const finallyMustCall = mustCall();
+  let resolveDestroy;
+  const destroyed = new Promise((resolve) => { resolveDestroy = resolve; });
+
+  async function* infiniteGenerate() {
+    try {
+      while (true) {
+        yield 'a';
+        await destroyed;
+      }
+    } finally {
+      finallyMustCall();
+    }
+  }
+
+  const stream = Readable.from(infiniteGenerate());
+
+  stream.on('data', (data) => {
+    strictEqual(data, 'a');
+    stream.destroy();
+    resolveDestroy();
+  });
+}
+
+Promise.all([
+  asyncSupport(),
+  syncSupport(),
+  syncPromiseSupport(),
+  syncRejectedSupport(),
+  noReturnAfterThrow(),
+  closeStreamWhileNextIsPending()
+]).then(mustCall());