stream: fix no data on partial decode

lib/_stream_readable.js

@@ -136,26 +136,33 @@ function readableAddChunk(stream, state, chunk, encoding, addToFront) {
       const e = new Error('stream.unshift() after end event');
       stream.emit('error', e);
     } else {
-      if (state.decoder && !addToFront && !encoding)
+      var skipAdd;
+      if (state.decoder && !addToFront && !encoding) {
         chunk = state.decoder.write(chunk);
+        skipAdd = (!state.objectMode && chunk.length === 0);
+      }
 
       if (!addToFront)
         state.reading = false;
 
-      // if we want the data now, just emit it.
-      if (state.flowing && state.length === 0 && !state.sync) {
-        stream.emit('data', chunk);
-        stream.read(0);
-      } else {
-        // update the buffer info.
-        state.length += state.objectMode ? 1 : chunk.length;
-        if (addToFront)
-          state.buffer.unshift(chunk);
-        else
-          state.buffer.push(chunk);
-
-        if (state.needReadable)
-          emitReadable(stream);
+      // Don't add to the buffer if we've decoded to an empty string chunk and
+      // we're not in object mode
+      if (!skipAdd) {
+        // if we want the data now, just emit it.
+        if (state.flowing && state.length === 0 && !state.sync) {
+          stream.emit('data', chunk);
+          stream.read(0);
+        } else {
+          // update the buffer info.
+          state.length += state.objectMode ? 1 : chunk.length;
+          if (addToFront)
+            state.buffer.unshift(chunk);
+          else
+            state.buffer.push(chunk);
+
+          if (state.needReadable)
+            emitReadable(stream);
+        }
       }
 
       maybeReadMore(stream, state);

test/parallel/test-stream2-decode-partial.js

@@ -0,0 +1,23 @@
+'use strict';
+require('../common');
+const Readable = require('_stream_readable');
+const assert = require('assert');
+
+var buf = '';
+const euro = new Buffer([0xE2, 0x82, 0xAC]);
+const cent = new Buffer([0xC2, 0xA2]);
+const source = Buffer.concat([euro, cent]);
+
+const readable = Readable({ encoding: 'utf8' });
+readable.push(source.slice(0, 2));
+readable.push(source.slice(2, 4));
+readable.push(source.slice(4, 6));
+readable.push(null);
+
+readable.on('data', function(data) {
+  buf += data;
+});
+
+process.on('exit', function() {
+  assert.strictEqual(buf, '€¢');
+});