Add a Rack endpoint for exporting charts as images

CHANGELOG.markdown

@@ -1,3 +1,7 @@
+# 3.0.1.5 / unreleased
+
+* Add a Rack endpoint for exporting charts to image files
+
 # 3.0.1 / 2013-04-09
 
 * Updated Highcharts to 3.0.1

README.markdown

@@ -45,6 +45,54 @@ Or one of the themes
 
 Other than that, refer to the [Highcharts documentation](http://highcharts.com/documentation/how-to-use)
 
+## Export endpoint
+
+This gem contains a Rack endpoint for converting the chart to a downloadable file.
+It is not required by default, so to use it, `require
+'highcharts/export_endpoint'`
+
+The endpoint is basically a port of the [PHP version made available](https://github.com/highslide-software/highcharts.com/blob/master/exporting-server/php/php-batik/index.php).
+It currently needs a lot of cleanup, but it is working fine for me. Your milage
+may vary.
+
+It uses [Apache Batik](http://xmlgraphics.apache.org/batik/) for the conversion, which must be
+installed separately, as well as a Java Runtime Environment.
+
+It expects to find a JRE in `/usr/bin/java`, and Batik in
+`/usr/share/java/batik-rasterizer.jar`, but both paths are configurable.
+
+Example usage in Rails:
+
+    # config/routes.rb
+    require 'highcharts/export_endpoint'
+
+    MyRailsApp::Application.routes.draw do
+      ...
+      mount Highcharts::ExportEndpoint.new({
+        java_path: "/usr/bin/java",
+        batik: "/usr/share/java/batik-rasterizer.jar"
+      }), at: "highcharts-export"
+      ...
+    end
+
+    # When rendering the chart
+    new Highcharts.Chart({
+      ...
+      exporting: {
+        url: "/highcharts-export",
+        ...
+      }
+    })
+
+### Cocaine
+
+The exporting endpoint uses [Cocaine](https://github.com/thoughtbot/cocaine) for
+handling the command lines and arguments and so on.
+
+I don't know a way to get optional dependencies in the gemspec, so for now
+that gets added whether you want it or not. I'd like to get this fixed,
+but would also like to avoid `begin; require 'cocaine'; rescue LoadError; ...; end` and similar hacks.
+
 ## Licensing
 
 Highcharts, which makes up the majority of this gem, has [its own, separate licensing](http://highcharts.com/license).

highcharts-rails.gemspec

@@ -17,6 +17,7 @@ Gem::Specification.new do |s|
   s.require_paths = ["lib"]
 
   s.add_dependency "railties", ">= 3.1"
+  s.add_dependency "cocaine",  "~> 0.4.0"
   s.add_development_dependency "bundler", "~> 1.0"
   s.add_development_dependency "rails",   ">= 3.1"
 end

lib/highcharts/export_endpoint.rb

@@ -0,0 +1,118 @@
+# encoding: utf-8
+require 'cocaine'
+
+module Highcharts
+  class ExportEndpoint
+    class InsecureSVGError      < ArgumentError; end
+    class MissingLibrary        < RuntimeError; end
+    class FailedToGenerateChart < RuntimeError; end
+    class InvalidType           < ArgumentError; end
+
+    attr_reader :output, :options
+
+    def initialize(options = {})
+      @options = default_options.merge(options)
+    end
+
+    def default_options
+      {
+        java_path: "/usr/bin/java",
+        batik: "/usr/share/java/batik-rasterizer.jar",
+      }
+    end
+
+    def call(env)
+      with_rescues do
+        raise MissingLibrary.new("Could not find batik-rasterizer.jar in #{options[:batik].inspect}") unless File.exists?(options[:batik].to_s)
+
+        request = Rack::Request.new(env)
+
+        filename = request.params["filename"].to_s
+        filename  = "chart" if filename.blank? || filename !~ /\A[A-Za-z0-9\-_ ]+\Z/
+
+        type     = request.params["type"].to_s
+        width    = request.params["width"].to_i
+        svg      = request.params["svg"].to_s
+
+        raise InsecureSVGError.new if svg.index("<!ENTITY") || svg.index("<!DOCTYPE")
+
+        if type == "image/svg+xml"
+          # We were sent SVG from the client, so can just render that back
+          return [200, {
+            'Content-Disposition' => "attachment; filename=\"#{filename}.svg\"",
+            'Content-Type'        => 'image/svg+xml'
+          }, [svg]]
+        end
+
+        width     = width > 0 ? width.to_s : "600"
+        extension = case type
+                    when "image/png"       then "png"
+                    when "image/jpeg"      then "jpg"
+                    when "application/pdf" then "pdf"
+                    when "image/svg+xml"   then "svg"
+                    else raise InvalidType.new("#{type} is not a valid type.")
+                    end
+
+        input     = write_svg_to_file(svg)
+        @output   = create_output_file(extension)
+
+        command.run(batik: options[:batik], outfile: output.path, type: type, width: width, infile: input.path)
+        input.close
+        content_length = output.size
+        output.rewind
+
+        raise FailedToGenerateChart.new("Nothing written to file") if !File.exists?(output.path) || content_length < 10
+
+        Rack::Response.new(self, 200, {
+          'Content-Disposition' => "attachment; filename=\"#{filename}.#{extension}\"",
+          'Content-Type'        => type
+        }).finish
+      end
+    end
+
+    # Pass the block along to the output file, and
+    # make sure to close the file afterwards
+    def each(&block)
+      output.each(&block)
+    ensure
+      output.close
+    end
+
+    def command
+      Cocaine::CommandLine.new(options[:java_path], "-jar :batik -m :type -d :outfile -w :width :infile")
+    end
+
+    def write_svg_to_file(contents)
+      file = ::Tempfile.new(["highcharts-input", ".svg"], Dir.tmpdir, encoding: 'utf-8')
+      file.puts contents
+      file.flush
+      file
+    end
+
+    def create_output_file(extension)
+      file = ::Tempfile.new(["highcharts-chart", ".#{extension}"])
+      file.binmode
+      file
+    end
+
+    def with_rescues
+      yield
+    rescue Highcharts::ExportEndpoint::InsecureSVGError => e
+      [400, {'Content-Type' => 'text/plain'}, ["The posted SVG could contain code for a malicious attack"]]
+    rescue Highcharts::ExportEndpoint::InvalidType => e
+      [400, {'Content-Type' => 'text/plain'}, [e]]
+    rescue Cocaine::CommandNotFoundError => e
+      [503, {'Content-Type' => 'text/plain'}, ["Unable to find required binary. #{e}"]]
+    rescue Highcharts::ExportEndpoint::MissingLibrary => e
+      [503, {'Content-Type' => 'text/plain'}, ["Unable to find required library. #{e}"]]
+    rescue Highcharts::ExportEndpoint::FailedToGenerateChart => e
+      [500, {'Content-Type' => 'text/plain'}, ["Failed to generate chart. More details may be available in the server logs."]]
+    rescue => e
+      [500, {'Content-Type' => 'text/plain'}, ["Something went wrong. More details may be available in the server logs."]]
+    end
+
+    def error(code, message)
+      [code, {}, [message].flatten]
+    end
+  end
+end