stream: add compose operator

PR-URL: #44937
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Robert Nagy <[email protected]>

doc/api/stream.md

@@ -1679,6 +1679,41 @@ option. In the code example above, data will be in a single chunk if the file
 has less then 64 KiB of data because no `highWaterMark` option is provided to
 [`fs.createReadStream()`][].
 
+##### `readable.compose(stream[, options])`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+* `stream` {Stream|Iterable|AsyncIterable|Function}
+* `options` {Object}
+  * `signal` {AbortSignal} allows destroying the stream if the signal is
+    aborted.
+* Returns: {Duplex} a stream composed with the stream `stream`.
+
+```mjs
+import { Readable } from 'node:stream';
+
+async function* splitToWords(source) {
+  for await (const chunk of source) {
+    const words = String(chunk).split(' ');
+
+    for (const word of words) {
+      yield word;
+    }
+  }
+}
+
+const wordsStream = Readable.from(['this is', 'compose as operator']).compose(splitToWords);
+const words = await wordsStream.toArray();
+
+console.log(words); // prints ['this', 'is', 'compose', 'as', 'operator']
+```
+
+See [`stream.compose`][] for more information.
+
 ##### `readable.iterator([options])`
 
 <!-- YAML
@@ -2698,6 +2733,8 @@ await finished(compose(s1, s2, s3));
 console.log(res); // prints 'HELLOWORLD'
 ```
 
+See [`readable.compose(stream)`][] for `stream.compose` as operator.
+
 ### `stream.Readable.from(iterable[, options])`
 
 <!-- YAML
@@ -4465,11 +4502,13 @@ contain multi-byte characters.
 [`process.stdin`]: process.md#processstdin
 [`process.stdout`]: process.md#processstdout
 [`readable._read()`]: #readable_readsize
+[`readable.compose(stream)`]: #readablecomposestream-options
 [`readable.map`]: #readablemapfn-options
 [`readable.push('')`]: #readablepush
 [`readable.setEncoding()`]: #readablesetencodingencoding
 [`stream.Readable.from()`]: #streamreadablefromiterable-options
 [`stream.addAbortSignal()`]: #streamaddabortsignalsignal-stream
+[`stream.compose`]: #streamcomposestreams
 [`stream.cork()`]: #writablecork
 [`stream.finished()`]: #streamfinishedstream-options-callback
 [`stream.pipe()`]: #readablepipedestination-options

lib/internal/streams/operators.js

@@ -4,6 +4,7 @@ const { AbortController } = require('internal/abort_controller');
 
 const {
   codes: {
+    ERR_INVALID_ARG_VALUE,
     ERR_INVALID_ARG_TYPE,
     ERR_MISSING_ARGS,
     ERR_OUT_OF_RANGE,
@@ -17,6 +18,11 @@ const {
 } = require('internal/validators');
 const { kWeakHandler } = require('internal/event_target');
 const { finished } = require('internal/streams/end-of-stream');
+const staticCompose = require('internal/streams/compose');
+const {
+  addAbortSignalNoValidate,
+} = require('internal/streams/add-abort-signal');
+const { isWritable, isNodeStream } = require('internal/streams/utils');
 
 const {
   ArrayPrototypePush,
@@ -32,6 +38,31 @@ const {
 const kEmpty = Symbol('kEmpty');
 const kEof = Symbol('kEof');
 
+function compose(stream, options) {
+  if (options != null) {
+    validateObject(options, 'options');
+  }
+  if (options?.signal != null) {
+    validateAbortSignal(options.signal, 'options.signal');
+  }
+
+  if (isNodeStream(stream) && !isWritable(stream)) {
+    throw new ERR_INVALID_ARG_VALUE('stream', stream, 'must be writable');
+  }
+
+  const composedStream = staticCompose(this, stream);
+
+  if (options?.signal) {
+    // Not validating as we already validated before
+    addAbortSignalNoValidate(
+      options.signal,
+      composedStream
+    );
+  }
+
+  return composedStream;
+}
+
 function map(fn, options) {
   if (typeof fn !== 'function') {
     throw new ERR_INVALID_ARG_TYPE(
@@ -392,6 +423,7 @@ module.exports.streamReturningOperators = {
   flatMap,
   map,
   take,
+  compose,
 };
 
 module.exports.promiseReturningOperators = {

test/parallel/test-stream-compose-operator.js

@@ -0,0 +1,127 @@
+'use strict';
+
+const common = require('../common');
+const {
+  Readable, Transform,
+} = require('stream');
+const assert = require('assert');
+
+{
+  // with async generator
+  const stream = Readable.from(['a', 'b', 'c', 'd']).compose(async function *(stream) {
+    let str = '';
+    for await (const chunk of stream) {
+      str += chunk;
+
+      if (str.length === 2) {
+        yield str;
+        str = '';
+      }
+    }
+  });
+  const result = ['ab', 'cd'];
+  (async () => {
+    for await (const item of stream) {
+      assert.strictEqual(item, result.shift());
+    }
+  })().then(common.mustCall());
+}
+
+{
+  // With Transformer
+  const stream = Readable.from(['a', 'b', 'c', 'd']).compose(new Transform({
+    objectMode: true,
+    transform: common.mustCall((chunk, encoding, callback) => {
+      callback(null, chunk);
+    }, 4)
+  }));
+  const result = ['a', 'b', 'c', 'd'];
+  (async () => {
+    for await (const item of stream) {
+      assert.strictEqual(item, result.shift());
+    }
+  })().then(common.mustCall());
+}
+
+{
+  // Throwing an error during `compose` (before waiting for data)
+  const stream = Readable.from([1, 2, 3, 4, 5]).compose(async function *(stream) { // eslint-disable-line require-yield
+
+    throw new Error('boom');
+  });
+
+  assert.rejects(async () => {
+    for await (const item of stream) {
+      assert.fail('should not reach here, got ' + item);
+    }
+  }, /boom/).then(common.mustCall());
+}
+
+{
+  // Throwing an error during `compose` (when waiting for data)
+  const stream = Readable.from([1, 2, 3, 4, 5]).compose(async function *(stream) {
+    for await (const chunk of stream) {
+      if (chunk === 3) {
+        throw new Error('boom');
+      }
+      yield chunk;
+    }
+  });
+
+  assert.rejects(
+    stream.toArray(),
+    /boom/,
+  ).then(common.mustCall());
+}
+
+{
+  // Throwing an error during `compose` (after finishing all readable data)
+  const stream = Readable.from([1, 2, 3, 4, 5]).compose(async function *(stream) { // eslint-disable-line require-yield
+
+    // eslint-disable-next-line no-unused-vars,no-empty
+    for await (const chunk of stream) {
+    }
+
+    throw new Error('boom');
+  });
+  assert.rejects(
+    stream.toArray(),
+    /boom/,
+  ).then(common.mustCall());
+}
+
+{
+  // AbortSignal
+  const ac = new AbortController();
+  const stream = Readable.from([1, 2, 3, 4, 5])
+    .compose(async function *(source) {
+      // Should not reach here
+      for await (const chunk of source) {
+        yield chunk;
+      }
+    }, { signal: ac.signal });
+
+  ac.abort();
+
+  assert.rejects(async () => {
+    for await (const item of stream) {
+      assert.fail('should not reach here, got ' + item);
+    }
+  }, {
+    name: 'AbortError',
+  }).then(common.mustCall());
+}
+
+{
+  assert.throws(
+    () => Readable.from(['a']).compose(Readable.from(['b'])),
+    { code: 'ERR_INVALID_ARG_VALUE' }
+  );
+}
+
+{
+  assert.throws(
+    () => Readable.from(['a']).compose(),
+    { code: 'ERR_INVALID_ARG_TYPE' }
+  );
+}

test/parallel/test-stream-compose.js

@@ -358,27 +358,24 @@ const assert = require('assert');
 }
 
 {
-  try {
-    compose();
-  } catch (err) {
-    assert.strictEqual(err.code, 'ERR_MISSING_ARGS');
-  }
+  assert.throws(
+    () => compose(),
+    { code: 'ERR_MISSING_ARGS' }
+  );
 }
 
 {
-  try {
-    compose(new Writable(), new PassThrough());
-  } catch (err) {
-    assert.strictEqual(err.code, 'ERR_INVALID_ARG_VALUE');
-  }
+  assert.throws(
+    () => compose(new Writable(), new PassThrough()),
+    { code: 'ERR_INVALID_ARG_VALUE' }
+  );
 }
 
 {
-  try {
-    compose(new PassThrough(), new Readable({ read() {} }), new PassThrough());
-  } catch (err) {
-    assert.strictEqual(err.code, 'ERR_INVALID_ARG_VALUE');
-  }
+  assert.throws(
+    () => compose(new PassThrough(), new Readable({ read() {} }), new PassThrough()),
+    { code: 'ERR_INVALID_ARG_VALUE' }
+  );
 }
 
 {