Latex server. Pass equations, get pngs

latex_server.rb

# Usage:                                                                                                                                       
#  ruby latex_server.rb                                                                                                                        
#                                                                                                                                              
# Try: <img src="http://localhost:4567/\cos \frac{\pi}{2} = 0">                                                                                
# Get: A nice looking png of: cos(pi/2) = 0                                                                                                    
#                                                                                                                                              
# Bug1: Ellipses (...) don't work. Probably the way urls are parsed                                                                            
#       by sinatra. Use \ldots                                                                                                                 
# Bug2: Question marks don't work. Definitely due to the way urls                                                                              
#       are parsed by any web library. Use \qmark                                                                                              
# Bug3: Commas dont work.. Not sure if they are necessary or
#       what to replace them with..?
#                                                                                                                                              
#
require 'tempfile'
require 'pathname'
require 'fileutils'
require 'digest/sha1'

FileUtils.mkdir_p File.dirname(__FILE__) + "/public" unless File.exists? "public"

def latex_doc(cmd)
  puts "cmd is #{cmd}"
  %Q{
    \\documentclass[10pt]{article}

    \\special{papersize=3in,5in}
    \\usepackage[utf8]{inputenc}
    \\pagestyle{empty}

    \\newcommand{\\qmark}{?}

    \\begin{document}

    $$#{cmd}$$

    \\end{document}
  }
end

def tmp(path)
  Dir.tmpdir + "/" + path
end

def target_public_path(cmd, opts = {})
  @realpath ||= Pathname.new(File.dirname(__FILE__)).realpath.to_s
  (@realpath + "/public/") + Digest::SHA1.hexdigest(cmd + opts.inspect) + ".png"
end

def latex2png(cmd, opts = {})
  return target_public_path(cmd, opts) if File.exists? target_public_path(cmd, opts)

  f = nil
  Tempfile.open("tmp.tex") do |f|
    f.write latex_doc(cmd)
  end

  Dir.chdir Dir.tmpdir do
    png_path = dvipng(tex2dvi(f.path), opts)
    puts "Copying #{png_path} to #{target_public_path(cmd)}"
    FileUtils.cp png_path, target_public_path(cmd, opts)
  end

  target_public_path(cmd, opts)
end

def tex2dvi(tex_path)
  result = `latex -interaction=nonstopmode #{tex_path}`
  (dvi_path = result.scan(/Output written on ([\w\.]+)/).first.first) rescue raise "No file match: #{result}"
  dvi_path
end

def dvipng(dvi_path, opts = {})
  png_path = dvi_path.split(".").first + ".png"
  system("dvipng -D #{opts[:res]} -T tight #{dvi_path} -o #{png_path}")
  png_path
end

require 'rubygems'
require 'sinatra'

# set_option :port, 8765                                                                                                                       

get '/:equation' do
  send_file latex2png(params[:equation], :res => 150), :type => "image/png", :disposition => 'inline'
end

get '/:resolution/:equation' do
  send_file latex2png(params[:equation], :res => params[:resolution]), :type => "image/png", :disposition => 'inline'
end