stream: Add stream.unshift(chunk)

lib/_stream_readable.js

@@ -106,10 +106,15 @@ function Readable(options) {
 // write() some more.
 Readable.prototype.push = function(chunk) {
   var state = this._readableState;
-  return readableAddChunk(this, state, chunk);
+  return readableAddChunk(this, state, chunk, false);
 };
 
-function readableAddChunk(stream, state, chunk) {
+Readable.prototype.unshift = function(chunk) {
+  var state = this._readableState;
+  return readableAddChunk(this, state, chunk, true);
+};
+
+function readableAddChunk(stream, state, chunk, addToFront) {
   state.reading = false;
 
   var er = chunkInvalid(state, chunk);
@@ -123,7 +128,10 @@ function readableAddChunk(stream, state, chunk) {
 
     // update the buffer info.
     state.length += state.objectMode ? 1 : chunk.length;
-    state.buffer.push(chunk);
+    if (addToFront)
+      state.buffer.unshift(chunk);
+    else
+      state.buffer.push(chunk);
 
     if (state.needReadable)
       emitReadable(stream);