GoBlockly Interpreter

GoBlockly Interpreter is an interpreter for the output of the Blockly visual programming editor.

What is Blockly?

Blockly is a web-based library for building visual programming editors, in which users can drag blocks together to build programs. Its focus is beginner programming education, but it's useful as a simple visual editing tool; the block-based rules for connecting statements together make syntax errors entirely impossible.

More information is available at https://developers.google.com/blockly.

What is the GoBlockly Interpreter?

The GoBlockly Interpreter is a go library for interpreting the output of the Blockly.Xml.domToText command from the Blockly library by interpreting the resulting XML as a program and running that program. It's useful for evaluating programs server-side and supports extending the interpreter with handling for your own blocks.

How do I use it?

Details are provided in the godocs of the library, but the basic overview is:

import (
	"bytes"
	"encoding/xml"
)

// XML may have come from client request or database store; it's the output of
Blockly.Xml.domToText in the Blockly library
func interpretBlockly(string xml) string {
	var blocks BlockXml
	if err := xml.Unmarshal(xmldata, &blocks); err {
		// Handle malformed XML here
	}
	var b bytes.Buffer
	var i Interpreter
	i.Console = &b
	i.FailHandler = func(reason string) {
		// Handle parser failure here
	}
	i.Run(blocks.Blocks)
	consoleOutput := b.String()
	return consoleOutput
}

The code runs server-side; how secure is it?

The GoBlockly interpreter offers no functionality beyond the basic Blockly blocks out of the box, and there are no exploits known that could allow the injection of arbitrary behavior via the interpreter. Of course, running user-provided code server-side always carries some risk; it is always recommended to run a server process with no more permissions than it needs to accomplish its goals on the host platform.

Why?

Generally, Blockly is converted client-side into code in another language and executed. Why write an interpreter?

As I rewrite Belphanior Butler in Go, I wish to recapitulate its ability to hand off the running of all of the servant manipulation server-side, so it seemed straightforward to recapitulate the Ruby interpreter for Blockly as a go interpreter (as opposed to, say, pulling in Node.js and running Blockly converted into JS server-side). This allows the server to both store the Blockly programs and execute them directly without having to loop through a web client.

Project Details

Project copyright 2015 Mark T. Tomczak.

Project is licensed under the Apache License, version 2.0 (see COPYING for more information).