stream: Return false from push() more properly

There are cases where a push() call would return true, even though
the thing being pushed was in fact way way larger than the high
water mark, simply because the 'needReadable' was already set, and
would not get unset until nextTick.

In some cases, this could lead to an infinite loop of pushing data
into the buffer, never getting to the 'readable' event which would
unset the needReadable flag.

Fix by splitting up the emitReadable function, so that it always
sets the flag on this tick, even if it defers until nextTick to
actually emit the event.

Also, if we're not ending or already in the process of reading, it
now calls read(0) if we're below the high water mark.  Thus, the
highWaterMark value is the intended amount to buffer up to, and it
is smarter about hitting the target.

lib/_stream_readable.js

@@ -327,19 +327,13 @@ function onread(stream, er, chunk) {
     return;
   }
 
-  // Don't emit readable right away in sync mode, because this can trigger
-  // another read() call => stack overflow.  This way, it might trigger
-  // a nextTick recursion warning, but that's not so bad.
-  if (state.needReadable) {
-    if (!sync)
-      emitReadable(stream);
-    else
-      process.nextTick(function() {
-        emitReadable(stream);
-      });
-  }
+  if (state.needReadable)
+    emitReadable(stream);
 }
 
+// Don't emit readable right away in sync mode, because this can trigger
+// another read() call => stack overflow.  This way, it might trigger
+// a nextTick recursion warning, but that's not so bad.
 function emitReadable(stream) {
   var state = stream._readableState;
   state.needReadable = false;
@@ -347,7 +341,28 @@ function emitReadable(stream) {
     return;
 
   state.emittedReadable = true;
+  if (state.sync)
+    process.nextTick(function() {
+      emitReadable_(stream);
+    });
+  else
+    emitReadable_(stream);
+}
+
+function emitReadable_(stream) {
+  var state = stream._readableState;
   stream.emit('readable');
+
+  // at this point, the user has presumably seen the 'readable' event,
+  // and called read() to consume some data.  that may have triggered
+  // in turn another _read(n,cb) call, in which case reading = true if
+  // it's in progress.
+  // However, if we're not ended, or reading, and the length < hwm,
+  // then go ahead and try to read some more right now preemptively.
+  if (!state.reading && !state.ending && !state.ended &&
+      state.length < state.highWaterMark) {
+    stream.read(0);
+  }
 }
 
 // abstract method.  to be overridden in specific implementation classes.

test/simple/test-stream-big-push.js

@@ -0,0 +1,84 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+var stream = require('stream');
+var str = 'asdfasdfasdfasdfasdf';
+
+var r = new stream.Readable({
+  highWaterMark: 5,
+  encoding: 'utf8'
+});
+
+var reads = 0;
+var eofed = false;
+var ended = false;
+
+r._read = function(n, cb) {
+  if (reads === 0) {
+    setTimeout(function() {
+      cb(null, str);
+    });
+    reads++;
+  } else if (reads === 1) {
+    var ret = r.push(str);
+    assert.equal(ret, false);
+    reads++;
+  } else {
+    assert(!eofed);
+    eofed = true;
+    cb(null, null);
+  }
+};
+
+r.on('end', function() {
+  ended = true;
+});
+
+// push some data in to start.
+// we've never gotten any read event at this point.
+var ret = r.push(str);
+// should be false.  > hwm
+assert(!ret);
+var chunk = r.read();
+assert.equal(chunk, str);
+chunk = r.read();
+assert.equal(chunk, null);
+
+r.once('readable', function() {
+  // this time, we'll get *all* the remaining data, because
+  // it's been added synchronously, as the read WOULD take
+  // us below the hwm, and so it triggered a _read() again,
+  // which synchronously added more, which we then return.
+  chunk = r.read();
+  assert.equal(chunk, str + str);
+
+  chunk = r.read();
+  assert.equal(chunk, null);
+});
+
+process.on('exit', function() {
+  assert(eofed);
+  assert(ended);
+  assert.equal(reads, 2);
+  console.log('ok');
+});