stream: make sure 'readable' is emitted before ending the stream

Fixes: https://github.com/nodejs/node/issues/25810

PR-URL: https://github.com/nodejs/node/pull/26059
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

lib/_stream_readable.js

@@ -505,20 +505,12 @@ function onEofChunk(stream, state) {
     }
   }
   state.ended = true;
+  state.needReadable = false;
 
-  if (state.sync) {
-    // If we are sync, wait until next tick to emit the data.
-    // Otherwise we risk emitting data in the flow()
-    // the readable code triggers during a read() call
-    emitReadable(stream);
-  } else {
-    // Emit 'readable' now to make sure it gets picked up.
-    state.needReadable = false;
-    if (!state.emittedReadable) {
-      state.emittedReadable = true;
-      emitReadable_(stream);
-    }
-  }
+  // We are not protecting if emittedReadable = true,
+  // so 'readable' gets scheduled anyway.
+  state.emittedReadable = true;
+  process.nextTick(emitReadable_, stream);
 }
 
 // Don't emit readable right away in sync mode, because this can trigger

lib/_stream_transform.js

@@ -116,9 +116,6 @@ function Transform(options) {
     writeencoding: null
   };
 
-  // Start out asking for a readable event once data is transformed.
-  this._readableState.needReadable = true;
-
   // We have implemented the _read method, and done the other things
   // that Readable wants before the first _read call, so unset the
   // sync guard flag.

test/parallel/test-http-readable-data-event.js

@@ -29,7 +29,7 @@ const server = http.createServer((req, res) => {
   };
 
   const expectedData = [helloWorld, helloAgainLater];
-  const expectedRead = [helloWorld, null, helloAgainLater, null];
+  const expectedRead = [helloWorld, null, helloAgainLater, null, null];
 
   const req = http.request(opts, (res) => {
     res.on('error', common.mustNotCall());
@@ -42,7 +42,7 @@ const server = http.createServer((req, res) => {
         assert.strictEqual(data, expectedRead.shift());
         next();
       } while (data !== null);
-    }, 2));
+    }, 3));
 
     res.setEncoding('utf8');
     res.on('data', common.mustCall((data) => {

test/parallel/test-stream-readable-emit-readable-short-stream.js

@@ -0,0 +1,146 @@
+'use strict';
+
+const common = require('../common');
+const stream = require('stream');
+const assert = require('assert');
+
+{
+  const r = new stream.Readable({
+    read: common.mustCall(function() {
+      this.push('content');
+      this.push(null);
+    })
+  });
+
+  const t = new stream.Transform({
+    transform: common.mustCall(function(chunk, encoding, callback) {
+      this.push(chunk);
+      return callback();
+    }),
+    flush: common.mustCall(function(callback) {
+      return callback();
+    })
+  });
+
+  r.pipe(t);
+  t.on('readable', common.mustCall(function() {
+    while (true) {
+      const chunk = t.read();
+      if (!chunk)
+        break;
+
+      assert.strictEqual(chunk.toString(), 'content');
+    }
+  }, 2));
+}
+
+{
+  const t = new stream.Transform({
+    transform: common.mustCall(function(chunk, encoding, callback) {
+      this.push(chunk);
+      return callback();
+    }),
+    flush: common.mustCall(function(callback) {
+      return callback();
+    })
+  });
+
+  t.end('content');
+
+  t.on('readable', common.mustCall(function() {
+    while (true) {
+      const chunk = t.read();
+      if (!chunk)
+        break;
+      assert.strictEqual(chunk.toString(), 'content');
+    }
+  }, 2));
+}
+
+{
+  const t = new stream.Transform({
+    transform: common.mustCall(function(chunk, encoding, callback) {
+      this.push(chunk);
+      return callback();
+    }),
+    flush: common.mustCall(function(callback) {
+      return callback();
+    })
+  });
+
+  t.write('content');
+  t.end();
+
+  t.on('readable', common.mustCall(function() {
+    while (true) {
+      const chunk = t.read();
+      if (!chunk)
+        break;
+      assert.strictEqual(chunk.toString(), 'content');
+    }
+  }, 2));
+}
+
+{
+  const t = new stream.Readable({
+    read() {
+    }
+  });
+
+  t.on('readable', common.mustCall(function() {
+    while (true) {
+      const chunk = t.read();
+      if (!chunk)
+        break;
+      assert.strictEqual(chunk.toString(), 'content');
+    }
+  }, 2));
+
+  t.push('content');
+  t.push(null);
+}
+
+{
+  const t = new stream.Readable({
+    read() {
+    }
+  });
+
+  t.on('readable', common.mustCall(function() {
+    while (true) {
+      const chunk = t.read();
+      if (!chunk)
+        break;
+      assert.strictEqual(chunk.toString(), 'content');
+    }
+  }, 2));
+
+  process.nextTick(() => {
+    t.push('content');
+    t.push(null);
+  });
+}
+
+{
+  const t = new stream.Transform({
+    transform: common.mustCall(function(chunk, encoding, callback) {
+      this.push(chunk);
+      return callback();
+    }),
+    flush: common.mustCall(function(callback) {
+      return callback();
+    })
+  });
+
+  t.on('readable', common.mustCall(function() {
+    while (true) {
+      const chunk = t.read();
+      if (!chunk)
+        break;
+      assert.strictEqual(chunk.toString(), 'content');
+    }
+  }, 2));
+
+  t.write('content');
+  t.end();
+}

test/parallel/test-stream-readable-emittedReadable.js

@@ -43,12 +43,23 @@ const noRead = new Readable({
   read: () => {}
 });
 
-noRead.on('readable', common.mustCall(() => {
+noRead.once('readable', common.mustCall(() => {
   // emittedReadable should be true when the readable event is emitted
   assert.strictEqual(noRead._readableState.emittedReadable, true);
   noRead.read(0);
   // emittedReadable is not reset during read(0)
   assert.strictEqual(noRead._readableState.emittedReadable, true);
+
+  noRead.on('readable', common.mustCall(() => {
+    // The second 'readable' is emitted because we are ending
+
+    // emittedReadable should be true when the readable event is emitted
+    assert.strictEqual(noRead._readableState.emittedReadable, false);
+    noRead.read(0);
+    // emittedReadable is not reset during read(0)
+    assert.strictEqual(noRead._readableState.emittedReadable, false);
+
+  }));
 }));
 
 noRead.push('foo');

test/parallel/test-stream-readable-needReadable.js

@@ -14,7 +14,7 @@ readable.on('readable', common.mustCall(() => {
   // When the readable event fires, needReadable is reset.
   assert.strictEqual(readable._readableState.needReadable, false);
   readable.read();
-}));
+}, 2));
 
 // If a readable listener is attached, then a readable event is needed.
 assert.strictEqual(readable._readableState.needReadable, true);
@@ -74,12 +74,14 @@ const slowProducer = new Readable({
 });
 
 slowProducer.on('readable', common.mustCall(() => {
-  if (slowProducer.read(8) === null) {
+  const chunk = slowProducer.read(8);
+  const state = slowProducer._readableState;
+  if (chunk === null) {
     // The buffer doesn't have enough data, and the stream is not need,
     // we need to notify the reader when data arrives.
-    assert.strictEqual(slowProducer._readableState.needReadable, true);
+    assert.strictEqual(state.needReadable, true);
   } else {
-    assert.strictEqual(slowProducer._readableState.needReadable, false);
+    assert.strictEqual(state.needReadable, false);
   }
 }, 4));
 

test/parallel/test-stream-readable-reading-readingMore.js

@@ -31,7 +31,7 @@ const Readable = require('stream').Readable;
     assert.strictEqual(state.reading, false);
   }
 
-  const expectedReadingMore = [true, false];
+  const expectedReadingMore = [true, false, false];
   readable.on('readable', common.mustCall(() => {
     // There is only one readingMore scheduled from on('data'),
     // after which everything is governed by the .read() call
@@ -40,10 +40,12 @@ const Readable = require('stream').Readable;
     // If the stream has ended, we shouldn't be reading
     assert.strictEqual(state.ended, !state.reading);
 
-    const data = readable.read();
-    if (data === null) // reached end of stream
+    // consume all the data
+    while (readable.read() !== null) {}
+
+    if (expectedReadingMore.length === 0) // reached end of stream
       process.nextTick(common.mustCall(onStreamEnd, 1));
-  }, 2));
+  }, 3));
 
   readable.on('end', common.mustCall(onStreamEnd));
   readable.push('pushed');

test/parallel/test-stream2-httpclient-response-end.js

@@ -11,8 +11,11 @@ const server = http.createServer(function(req, res) {
     let data = '';
     res.on('readable', common.mustCall(function() {
       console.log('readable event');
-      data += res.read();
-    }));
+      let chunk;
+      while ((chunk = res.read()) !== null) {
+        data += chunk;
+      }
+    }, 2));
     res.on('end', common.mustCall(function() {
       console.log('end event');
       assert.strictEqual(msg, data);

test/parallel/test-stream2-transform.js

@@ -321,11 +321,16 @@ const Transform = require('_stream_transform');
 
   pt.end();
 
-  assert.strictEqual(emits, 1);
-  assert.strictEqual(pt.read(5).toString(), 'l');
-  assert.strictEqual(pt.read(5), null);
+  // The next readable is emitted on the next tick.
+  assert.strictEqual(emits, 0);
 
-  assert.strictEqual(emits, 1);
+  process.on('nextTick', function() {
+    assert.strictEqual(emits, 1);
+    assert.strictEqual(pt.read(5).toString(), 'l');
+    assert.strictEqual(pt.read(5), null);
+
+    assert.strictEqual(emits, 1);
+  });
 }
 
 {