streams2: Process write buffer in a loop, not recursively

This fixes pummel/test-net-write-callbacks

lib/_stream_writable.js

@@ -219,6 +219,49 @@ function onwrite(stream, er) {
       stream.emit('drain');
     });
   }
+
+  // if there's something in the buffer waiting, then process it
+  // It would be nice if there were TCO in JS, and we could just
+  // shift the top off the buffer and _write that, but that approach
+  // causes RangeErrors when you have a very large number of very
+  // small writes, and is not very efficient otherwise.
+  if (!state.bufferProcessing && state.buffer.length) {
+    state.bufferProcessing = true;
+
+    for (var c = 0; c < state.buffer.length; c++) {
+      var chunkCb = state.buffer[c];
+      var chunk = chunkCb[0];
+      cb = chunkCb[1];
+
+      if (false === state.decodeStrings)
+        l = chunk[0].length;
+      else
+        l = chunk.length;
+
+      state.writelen = l;
+      state.writecb = cb;
+      state.writechunk = chunk;
+      state.writing = true;
+      state.sync = true;
+      stream._write(chunk, state.onwrite);
+      state.sync = false;
+
+      // if we didn't call the onwrite immediately, then
+      // it means that we need to wait until it does.
+      // also, that means that the chunk and cb are currently
+      // being processed, so move the buffer counter past them.
+      if (state.writing) {
+        c++;
+        break;
+      }
+    }
+
+    state.bufferProcessing = false;
+    if (c < state.buffer.length)
+      state.buffer = state.buffer.slice(c);
+    else
+      state.buffer.length = 0;
+  }
 }
 
 Writable.prototype._write = function(chunk, cb) {