stream: Don't signal EOF on '' or Buffer(0)

Those values, if passed to the _read() cb, will not signal an EOF. Only null or undefined will mark the end of data, and trigger the end event. However, great care must be taken if you are returning an empty string or buffer! There must be some other thing somewhere that will trigger a read() call, because there will never be a readable event fired later. This is in preparation for CryptoStreams being ported to streams2, where it is safe to simply stop reading, because the crypto cycle process will cause it to read(0) again at some future date.
nodejs · Jan 31, 2013 · 8916a6c · 8916a6c
1 parent 0168109
commit 8916a6c
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Showing 2 changed files with 99 additions and 7 deletions.
diff --git a/lib/_stream_readable.js b/lib/_stream_readable.js
@@ -271,9 +271,7 @@ function onread(stream, er, chunk) {
   if (er)
     return stream.emit('error', er);
 
-  if (chunk === null ||
-      chunk === undefined ||
-      (!state.objectMode && !chunk.length)) {
+  if (chunk === null || chunk === undefined) {
     // eof
     state.ended = true;
     if (state.decoder) {
@@ -296,11 +294,20 @@ function onread(stream, er, chunk) {
   if (state.decoder)
     chunk = state.decoder.write(chunk);
 
+  // at this point, if we got a zero-length buffer or string,
+  // and we're not in object-mode, then there's really no point
+  // continuing.  it means that there is nothing to read right
+  // now, but as we have not received the EOF-signaling null,
+  // we're not ended.  we've already unset the reading flag,
+  // so just get out of here.
+  if (!state.objectMode &&
+      (chunk || typeof chunk === 'string') &&
+      0 === chunk.length)
+    return;
+
   // update the buffer info.
-  if (chunk || (state.objectMode && chunk !== undefined && chunk !== null)) {
-    state.length += state.objectMode ? 1 : chunk.length;
-    state.buffer.push(chunk);
-  }
+  state.length += state.objectMode ? 1 : chunk.length;
+  state.buffer.push(chunk);
 
   // if we haven't gotten enough to pass the lowWaterMark,
   // and we haven't ended, then don't bother telling the user

diff --git a/test/simple/test-stream2-readable-empty-buffer-no-eof.js b/test/simple/test-stream2-readable-empty-buffer-no-eof.js
@@ -0,0 +1,85 @@
+// 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 Readable = require('stream').Readable;
+
+var r = new Readable();
+
+// should not end when we get a Buffer(0) or '' as the _read result
+// that just means that there is *temporarily* no data, but to go
+// ahead and try again later.
+//
+// note that this is very unusual.  it only works for crypto streams
+// because the other side of the stream will call read(0) to cycle
+// data through openssl.  that's why we set the timeouts to call
+// r.read(0) again later, otherwise there is no more work being done
+// and the process just exits.
+
+var buf = new Buffer(5);
+buf.fill('x');
+var reads = 5;
+r._read = function(n, cb) {
+  switch (reads--) {
+    case 0:
+      return cb(null, null); // EOF
+    case 1:
+      return cb(null, buf);
+    case 2:
+      setTimeout(r.read.bind(r, 0), 10);
+      return cb(null, new Buffer(0)); // Not-EOF!
+    case 3:
+      setTimeout(r.read.bind(r, 0), 10);
+      return process.nextTick(function() {
+        return cb(null, new Buffer(0));
+      });
+    case 4:
+      setTimeout(r.read.bind(r, 0), 10);
+      return setTimeout(function() {
+        return cb(null, new Buffer(0));
+      });
+    case 5:
+      return setTimeout(function() {
+        return cb(null, buf);
+      });
+    default:
+      throw new Error('unreachable');
+  }
+};
+
+var results = [];
+function flow() {
+  var chunk;
+  while (null !== (chunk = r.read()))
+    results.push(chunk + '');
+}
+r.on('readable', flow);
+r.on('end', function() {
+  results.push('EOF');
+});
+flow();
+
+process.on('exit', function() {
+  assert.deepEqual(results, [ 'xxxxx', 'xxxxx', 'EOF' ]);
+  console.log('ok');
+});