Rack middleware for inline Graphviz graphs

gviz.rb

require 'digest'

module GViz

  CACHE_PATH  = "/tmp/gviz/"
  ENGINES = %w{dot neato twopi circo fdp sfdp}

  XSLTPROC = `which xsltproc`.chomp
  notugly = File.dirname(__FILE__)+"/notugly.xsl"
  NOTUGLY  = (File.exists?(notugly) && XSLTPROC != "") ? notugly : nil
  CONVERT = `which convert`

  class Graph
    def initialize(graph)
      @graph = graph
    end
    
    def slug
      # The MD5 hash is not for security, since I'm not accepting posted graphs,
      # nor keeping any private graphs. 
      @slug ||= Digest::MD5.hexdigest(@graph)
    end

    def write(fname)
      `mkdir -p #{CACHE_PATH}`
      File.open(fname,"w") do |f|
        f.write(@graph)
      end
    end

    def cache
      fname = "#{CACHE_PATH}#{slug}.dot"
      write(fname) if !File.exists?(fname)
      slug
    end

    def self.dot_file(slug)
      "#{CACHE_PATH}#{slug}.dot"
    end
  end

  class Cache
    def initialize hash,engine,format
      @hash   = hash
      @engine = engine
      @format = format

      raise "Unsupported layout" if !ENGINES.member?(@engine.to_s)
    end

    def layout(format, src, dest)
      system("#{@engine.to_s} -T#{format.to_s} #{src} -o #{dest}")
    end
    def xsl(src,dest)
      system("#{XSLTPROC} --nonet #{NOTUGLY} #{src} >#{dest}")
    end

    def convert(src,dest)
      system("convert #{src} #{dest}")
    end

    def target_file(format=nil)
      format ||= @format
      CACHE_PATH+@hash+".#{format.to_s}"
    end

    def render(format=nil)
      format ||= @format
      src  = Graph.dot_file(@hash)
      dest = target_file(format)

      if (format.to_sym == :svg && NOTUGLY)
        layout(format,src,dest +".tmp")
        xsl(dest+".tmp",dest)
      elsif NOTUGLY && CONVERT != ""
        layout(:svg, src, dest+".tmp")
        xsl(dest+".tmp",dest+".tmp.svg")
        convert(dest+".tmp.svg",dest)
      else
        layout(format,src,dest)
      end
      File.read(dest) rescue nil
    end


    def url(url_base)
      "#{url_base}#{@engine}_#{@hash}.#{@format}"
    end

    def img_link(url_base)
      "<img src='#{url(url_base)}' class='gviz' />"
    end

    def to_html(url_base="/images/gviz/")
      return img_link(url_base) if @format != :inline_svg
      svg = render(:svg)
      svg = svg.split("\n")[2..-1] # Strip xml declaration and doctype
      svg.join("\n")
    end

    def file
      file = File.read(target_file) rescue nil
      return file if file
      render
    end
    def xsl(src,dest)
      system("#{XSLTPROC} --nonet #{NOTUGLY} #{src} >#{dest}")
    end

    def convert(src,dest)
      system("convert #{src} #{dest}")
    end

    def target_file(format=nil)
      format ||= @format
      CACHE_PATH+@hash+".#{format.to_s}"
    end

    def render(format=nil)
      format ||= @format
      src  = Graph.dot_file(@hash)
      dest = target_file(format)

      if (format.to_sym == :svg && NOTUGLY)
        layout(format,src,dest +".tmp")
        xsl(dest+".tmp",dest)
      elsif NOTUGLY && CONVERT != ""
        layout(:svg, src, dest+".tmp")
        xsl(dest+".tmp",dest+".tmp.svg")
        convert(dest+".tmp.svg",dest)
      else
        layout(format,src,dest)
      end
      File.read(dest) rescue nil
    end


    def url(url_base)
      "#{url_base}#{@engine}_#{@hash}.#{@format}"
    end

    def img_link(url_base)
      "<img src='#{url(url_base)}' class='gviz' />"
    end

    def to_html(url_base="/images/gviz/")
      return img_link(url_base) if @format != :inline_svg
      svg = render(:svg)
      svg = svg.split("\n")[2..-1] # Strip xml declaration and doctype
      svg.join("\n")
    end

    def file
      file = File.read(target_file) rescue nil
      return file if file
      render
    end

  end

  #
  # Cache the graph, and return either a link, or inline SVG depending
  # on the preferred format
  #
  def self.graph_to_html(engine,graph,preferred_format=:inline_svg, url_base="/images/gviz/")
    hash = Graph.new(graph).cache
    Cache.new(hash,engine,preferred_format).to_html(url_base)
  end
end

gviz_controller.rb

require 'lib/gviz'

require 'rack'

module GViz

  class Controller
    def initialize app, base = "/images/gviz/"
      @app = app
      @base = base
      @uri_regexp = /^(#{ENGINES.join("|")})_([0-9a-f]{32}).(png|svg)$/
    end


    def call env
      uri = env["REQUEST_URI"]

      if (uri[0.. @base.size-1] != @base)
        return @app.call(env) if @app
        return Rack::Response.new("(empty)").finish
      end

      match = uri[@base.size .. -1].match(@uri_regexp)
      if !match
        return Rack::Response.new("Invalid URL",403)
      end

      engine = match[1]
      hash   = match[2]
      format = match[3]

      cache = GViz::Cache.new(hash,engine,format)
      file = cache.file
      return Rack::Response.new("No such graph",404) if !file

      r = Rack::Response.new
      r["Content-Type"] = format == "png" ? "image/png" : "image/svg+xml"
      r.write(file)
      r.finish
    end
  end

end