無料のサービスを使ってHubotで動的に画像を生成して返す ref: http://qiita.com/daxanya1/items/a352e894491bd396a97d

fabric.js

(function() {
  var fabric, fs, mktemp, d3;

  d3 = require('d3');
  mktemp = require('mktemp');
  fabric = require('fabric').fabric;
  fs = require('fs');
  path = require('path');

  module.exports = function(robot) {
    return robot.hear(/rect ([0-9]+) ([0-9]+) ([0-9]+) ([0-9]+) (\w+)/, function(bot) {
      var svg, temppath;
      var width = 750;
      var height = 750;
      d3.select("body").node().innerHTML = '';
      var svgimage = d3.select("body").append("svg").attr({"width": width, "height": height });
      svgimage.append('rect')
      .attr({
        x:bot.match[1],
        y:bot.match[2],
        width:bot.match[3],
        height:bot.match[4],
        fill:bot.match[5]
      });
      robot.send(bot.envelope, "writing..");
      var canvas = fabric.createCanvasForNode(width, height);
      temppath = path.join(__dirname, '..', 'tmp');
      url = process.env.HEROKU_URL
      if (url === undefined) {
        url = 'http://localhost:8080'
      }
      var svg = d3.select('body').node().innerHTML;
      console.log(svg);
      fabric.loadSVGFromString(svg , function(objects, options) {
        options.top = 0;
        options.left = 0;
        for (var i=0; i<objects.length; i++) {
          objects[i].set ({ angle: 10 });
        }
        var svgGroups = fabric.util.groupSVGElements(objects, options);
        canvas.add(svgGroups).renderAll();
        try {
          fs.statSync(temppath);
        } catch (e) {
          console.log(e);
          fs.mkdirSync(temppath, 0700);
        }
        mktemp.createFile(path.join(temppath,'XXXXXXXX.png'), function(err, filename) {
          var outStream, stream;
          stream = canvas.createPNGStream();
          outStream = fs.createWriteStream(filename);
          outStream.on('close', function() {
            robot.send(bot.envelope, url + "/hubot/tempget.png?id=" + path.basename(filename));
          });
          stream.on('data', function(chunk) {
            outStream.write(chunk);
          });
          stream.on('end', function(chunk) {
            outStream.end();
          });
        });
      });
    });
  };
}).call(this);

file0.txt

$ npm install --save d3

file1.txt

$ npm install --save canvas
$ npm install --save canvg

file2.txt

heroku config:add BUILDPACK_URL=https://github.com/mojodna/heroku-buildpack-multi.git#build-env

file3.txt

$ npm install --save mktemp

file6.txt

$ npm uninstall --save canvg
$ npm install --save fabric

svg.js

// Generated by CoffeeScript 1.6.3
(function() {
  var Canvas, canvg, fs, mktemp, d3;

  d3 = require('d3');
  Canvas = require('canvas');
  mktemp = require('mktemp');
  canvg = require('canvg');
  fs = require('fs');
  path = require('path');

  module.exports = function(robot) {
    return robot.hear(/svg ([0-9]+) ([0-9]+) ([0-9]+) (\w+)/, function(bot) {
      var canvas, svg, temppath;
      var width = 750;
      var height = 750;
      d3.select("body").node().innerHTML = '';
      var svgimage = d3.select("body").append("svg").attr({"width": width, "height": height });
      svgimage.append('circle')
      .attr({
        cx:bot.match[1],
        cy:bot.match[2],
        r:bot.match[3],
        fill:bot.match[4]
      });
      robot.send(bot.envelope, "writing..");
      canvas = new Canvas(width, height);
      temppath = path.join(__dirname, '..', 'tmp');
      url = process.env.HEROKU_URL
      if (url === undefined) {
        url = 'http://localhost:8080'
      }
      var svg = d3.select('body').node().innerHTML;
      canvg(canvas, svg, {
        renderCallback: function() {
          try {
            fs.statSync(temppath);
          } catch (e) {
            console.log(e);
            fs.mkdirSync(temppath, 0700);
          }
          mktemp.createFile(path.join(temppath,'XXXXXXXX.png'), function(err, filename) {
            var outStream, stream;
            stream = canvas.createPNGStream();
            outStream = fs.createWriteStream(filename);
            outStream.on('close', function() {
              robot.send(bot.envelope, url + "/hubot/tempget.png?id=" + path.basename(filename));
            });
            stream.on('data', function(chunk) {
              outStream.write(chunk);
            });
            stream.on('end', function(chunk) {
              outStream.end();
            });
          });
        }
      });
    });
  };
}).call(this);

tempget.coffee

querystring = require('querystring')
fs = require('fs')
path = require('path')

module.exports = (robot) ->
  robot.router.get "/hubot/tempget.png", (req, res) ->
    query = querystring.parse(req._parsedUrl.query)
    tmp = path.join(__dirname, '..', 'tmp',query.id)
    path.exists(tmp, (exists) ->
      if(exists)
        console.log "exist! #{tmp}"
        fs.readFile tmp,(err,data) ->
          res.writeHead(200, {'Content-Type': 'image/png'})
          res.end(data);
      else
        console.log "not! #{tmp}"
        res.status(404).send('Not found')
    )