[v16.x backport] stream: add stream.compose

doc/api/stream.md

@@ -1918,6 +1918,95 @@ run().catch(console.error);
 after the `callback` has been invoked. In the case of reuse of streams after
 failure, this can cause event listener leaks and swallowed errors.
 
+### `stream.compose(...streams)`
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - `stream.compose` is experimental.
+
+* `streams` {Stream[]|Iterable[]|AsyncIterable[]|Function[]}
+* Returns: {stream.Duplex}
+
+Combines two or more streams into a `Duplex` stream that writes to the
+first stream and reads from the last. Each provided stream is piped into
+the next, using `stream.pipeline`. If any of the streams error then all
+are destroyed, including the outer `Duplex` stream.
+
+Because `stream.compose` returns a new stream that in turn can (and
+should) be piped into other streams, it enables composition. In contrast,
+when passing streams to `stream.pipeline`, typically the first stream is
+a readable stream and the last a writable stream, forming a closed
+circuit.
+
+If passed a `Function` it must be a factory method taking a `source`
+`Iterable`.
+
+```mjs
+import { compose, Transform } from 'stream';
+
+const removeSpaces = new Transform({
+  transform(chunk, encoding, callback) {
+    callback(null, String(chunk).replace(' ', ''));
+  }
+});
+
+async function* toUpper(source) {
+  for await (const chunk of source) {
+    yield String(chunk).toUpperCase();
+  }
+}
+
+let res = '';
+for await (const buf of compose(removeSpaces, toUpper).end('hello world')) {
+  res += buf;
+}
+
+console.log(res); // prints 'HELLOWORLD'
+```
+
+`stream.compose` can be used to convert async iterables, generators and
+functions into streams.
+
+* `AsyncIterable` converts into a readable `Duplex`. Cannot yield
+  `null`.
+* `AsyncGeneratorFunction` converts into a readable/writable transform `Duplex`.
+  Must take a source `AsyncIterable` as first parameter. Cannot yield
+  `null`.
+* `AsyncFunction` converts into a writable `Duplex`. Must return
+  either `null` or `undefined`.
+
+```mjs
+import { compose } from 'stream';
+import { finished } from 'stream/promises';
+
+// Convert AsyncIterable into readable Duplex.
+const s1 = compose(async function*() {
+  yield 'Hello';
+  yield 'World';
+}());
+
+// Convert AsyncGenerator into transform Duplex.
+const s2 = compose(async function*(source) {
+  for await (const chunk of source) {
+    yield String(chunk).toUpperCase();
+  }
+});
+
+let res = '';
+
+// Convert AsyncFunction into writable Duplex.
+const s3 = compose(async function(source) {
+  for await (const chunk of source) {
+    res += chunk;
+  }
+});
+
+await finished(compose(s1, s2, s3));
+
+console.log(res); // prints 'HELLOWORLD'
+```
+
 ### `stream.Readable.from(iterable, [options])`
 <!-- YAML
 added:

lib/internal/streams/compose.js

@@ -0,0 +1,196 @@
+'use strict';
+
+const pipeline = require('internal/streams/pipeline');
+const Duplex = require('internal/streams/duplex');
+const { destroyer } = require('internal/streams/destroy');
+const {
+  isNodeStream,
+  isReadable,
+  isWritable,
+} = require('internal/streams/utils');
+const {
+  AbortError,
+  codes: {
+    ERR_INVALID_ARG_VALUE,
+    ERR_MISSING_ARGS,
+  },
+} = require('internal/errors');
+
+// This is needed for pre node 17.
+class ComposeDuplex extends Duplex {
+  constructor(options) {
+    super(options);
+
+    // https://github.com/nodejs/node/pull/34385
+
+    if (options?.readable === false) {
+      this._readableState.readable = false;
+      this._readableState.ended = true;
+      this._readableState.endEmitted = true;
+    }
+
+    if (options?.writable === false) {
+      this._writableState.writable = false;
+      this._writableState.ending = true;
+      this._writableState.ended = true;
+      this._writableState.finished = true;
+    }
+  }
+}
+
+module.exports = function compose(...streams) {
+  if (streams.length === 0) {
+    throw new ERR_MISSING_ARGS('streams');
+  }
+
+  if (streams.length === 1) {
+    return Duplex.from(streams[0]);
+  }
+
+  const orgStreams = [...streams];
+
+  if (typeof streams[0] === 'function') {
+    streams[0] = Duplex.from(streams[0]);
+  }
+
+  if (typeof streams[streams.length - 1] === 'function') {
+    const idx = streams.length - 1;
+    streams[idx] = Duplex.from(streams[idx]);
+  }
+
+  for (let n = 0; n < streams.length; ++n) {
+    if (!isNodeStream(streams[n])) {
+      // TODO(ronag): Add checks for non streams.
+      continue;
+    }
+    if (n < streams.length - 1 && !isReadable(streams[n])) {
+      throw new ERR_INVALID_ARG_VALUE(
+        `streams[${n}]`,
+        orgStreams[n],
+        'must be readable'
+      );
+    }
+    if (n > 0 && !isWritable(streams[n])) {
+      throw new ERR_INVALID_ARG_VALUE(
+        `streams[${n}]`,
+        orgStreams[n],
+        'must be writable'
+      );
+    }
+  }
+
+  let ondrain;
+  let onfinish;
+  let onreadable;
+  let onclose;
+  let d;
+
+  function onfinished(err) {
+    const cb = onclose;
+    onclose = null;
+
+    if (cb) {
+      cb(err);
+    } else if (err) {
+      d.destroy(err);
+    } else if (!readable && !writable) {
+      d.destroy();
+    }
+  }
+
+  const head = streams[0];
+  const tail = pipeline(streams, onfinished);
+
+  const writable = !!isWritable(head);
+  const readable = !!isReadable(tail);
+
+  // TODO(ronag): Avoid double buffering.
+  // Implement Writable/Readable/Duplex traits.
+  // See, https://github.com/nodejs/node/pull/33515.
+  d = new ComposeDuplex({
+    // TODO (ronag): highWaterMark?
+    writableObjectMode: !!head?.writableObjectMode,
+    readableObjectMode: !!tail?.writableObjectMode,
+    writable,
+    readable,
+  });
+
+  if (writable) {
+    d._write = function(chunk, encoding, callback) {
+      if (head.write(chunk, encoding)) {
+        callback();
+      } else {
+        ondrain = callback;
+      }
+    };
+
+    d._final = function(callback) {
+      head.end();
+      onfinish = callback;
+    };
+
+    head.on('drain', function() {
+      if (ondrain) {
+        const cb = ondrain;
+        ondrain = null;
+        cb();
+      }
+    });
+
+    tail.on('finish', function() {
+      if (onfinish) {
+        const cb = onfinish;
+        onfinish = null;
+        cb();
+      }
+    });
+  }
+
+  if (readable) {
+    tail.on('readable', function() {
+      if (onreadable) {
+        const cb = onreadable;
+        onreadable = null;
+        cb();
+      }
+    });
+
+    tail.on('end', function() {
+      d.push(null);
+    });
+
+    d._read = function() {
+      while (true) {
+        const buf = tail.read();
+
+        if (buf === null) {
+          onreadable = d._read;
+          return;
+        }
+
+        if (!d.push(buf)) {
+          return;
+        }
+      }
+    };
+  }
+
+  d._destroy = function(err, callback) {
+    if (!err && onclose !== null) {
+      err = new AbortError();
+    }
+
+    onreadable = null;
+    ondrain = null;
+    onfinish = null;
+
+    if (onclose === null) {
+      callback(err);
+    } else {
+      onclose = callback;
+      destroyer(tail, err);
+    }
+  };
+
+  return d;
+};

lib/internal/streams/duplexify.js

@@ -3,12 +3,11 @@
 const {
   isIterable,
   isNodeStream,
-  isDestroyed,
+  isReadable,
   isReadableNodeStream,
+  isWritable,
   isWritableNodeStream,
   isDuplexNodeStream,
-  isReadableFinished,
-  isWritableEnded,
 } = require('internal/streams/utils');
 const eos = require('internal/streams/end-of-stream');
 const {
@@ -32,20 +31,6 @@ const {
   FunctionPrototypeCall
 } = primordials;
 
-function isReadable(stream) {
-  const r = isReadableNodeStream(stream);
-  if (r === null || typeof stream?.readable !== 'boolean') return null;
-  if (isDestroyed(stream)) return false;
-  return r && stream.readable && !isReadableFinished(stream);
-}
-
-function isWritable(stream) {
-  const r = isWritableNodeStream(stream);
-  if (r === null || typeof stream?.writable !== 'boolean') return null;
-  if (isDestroyed(stream)) return false;
-  return r && stream.writable && !isWritableEnded(stream);
-}
-
 // This is needed for pre node 17.
 class Duplexify extends Duplex {
   constructor(options) {

lib/internal/streams/end-of-stream.js

@@ -176,6 +176,8 @@ function eos(stream, options, callback) {
     (rState && rState.errorEmitted) ||
     (rState && stream.req && stream.aborted) ||
     (
+      (!wState || !willEmitClose || typeof wState.closed !== 'boolean') &&
+      (!rState || !willEmitClose || typeof rState.closed !== 'boolean') &&
       (!writable || (wState && wState.finished)) &&
       (!readable || (rState && rState.endEmitted))
     )

lib/internal/streams/pipeline.js

@@ -27,8 +27,8 @@ const { validateCallback } = require('internal/validators');
 
 const {
   isIterable,
-  isReadable,
-  isStream,
+  isReadableNodeStream,
+  isNodeStream,
 } = require('internal/streams/utils');
 
 let PassThrough;
@@ -87,7 +87,7 @@ function popCallback(streams) {
 function makeAsyncIterable(val) {
   if (isIterable(val)) {
     return val;
-  } else if (isReadable(val)) {
+  } else if (isReadableNodeStream(val)) {
     // Legacy streams are not Iterable.
     return fromReadable(val);
   }
@@ -204,7 +204,7 @@ function pipeline(...streams) {
     const reading = i < streams.length - 1;
     const writing = i > 0;
 
-    if (isStream(stream)) {
+    if (isNodeStream(stream)) {
       finishCount++;
       destroys.push(destroyer(stream, reading, writing, finish));
     }
@@ -216,7 +216,7 @@ function pipeline(...streams) {
           throw new ERR_INVALID_RETURN_VALUE(
             'Iterable, AsyncIterable or Stream', 'source', ret);
         }
-      } else if (isIterable(stream) || isReadable(stream)) {
+      } else if (isIterable(stream) || isReadableNodeStream(stream)) {
         ret = stream;
       } else {
         ret = Duplex.from(stream);
@@ -269,8 +269,8 @@ function pipeline(...streams) {
         finishCount++;
         destroys.push(destroyer(ret, false, true, finish));
       }
-    } else if (isStream(stream)) {
-      if (isReadable(ret)) {
+    } else if (isNodeStream(stream)) {
+      if (isReadableNodeStream(ret)) {
         ret.pipe(stream);
 
         // Compat. Before node v10.12.0 stdio used to throw an error so
@@ -291,9 +291,6 @@ function pipeline(...streams) {
     }
   }
 
-  // TODO(ronag): Consider returning a Duplex proxy if the first argument
-  // is a writable. Would improve composability.
-  // See, https://github.com/nodejs/node/issues/32020
   return ret;
 }