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require 'net/smtp'
require 'tmail'
require 'erb'

module Rack
  # Catches all exceptions raised from the app it wraps and
  # sends a useful email with the exception, stacktrace, and
  # contents of the environment.

  class MailExceptions
    attr_reader :config

    def initialize(app)
      @app = app
      @config = {
        :to => nil,
        :from => ENV['USER'] || 'rack',
        :subject => '[exception] %s',
        :smtp => {
          :server => 'localhost',
          :domain => 'localhost',
          :port => 25,
          :authentication => :login,
          :user_name => nil,
          :password => nil
        }
      }
      @template = ERB.new(TEMPLATE)
      yield self if block_given?
    end

    def call(env)
      status, headers, body =
        begin
          @app.call(env)
        rescue => boom
          # TODO don't allow exceptions from send_notification to
          # propogate
          send_notification boom, env
          raise
        end
      send_notification env['mail.exception'], env if env['mail.exception']
      [status, headers, body]
    end

    %w[to from subject].each do |meth|
      define_method(meth) { |value| @config[meth.to_sym] = value }
    end

    def smtp(settings={})
      @config[:smtp].merge! settings
    end

  private
    def generate_mail(exception, env)
      mail = TMail::Mail.new
      mail.to = Array(config[:to])
      mail.from = config[:from]
      mail.subject = config[:subject] % [exception.to_s]
      mail.date = Time.now
      mail.set_content_type 'text/plain'
      mail.charset = 'UTF-8'
      mail.body = @template.result(binding)
      mail
    end

    def send_notification(exception, env)
      mail = generate_mail(exception, env)
      smtp = config[:smtp]
      env['mail.sent'] = true
      return if smtp[:server] == 'example.com'

      Net::SMTP.start smtp[:server], smtp[:port], smtp[:domain], smtp[:user_name], smtp[:password], smtp[:authentication] do |server|
        mail.to.each do |recipient|
          server.send_message mail.to_s, mail.from, recipient
        end
      end
    end

    def extract_body(env)
      if io = env['rack.input']
        io.rewind if io.respond_to?(:rewind)
        io.read
      end
    end

    TEMPLATE = (<<-'EMAIL').gsub(/^ {4}/, '')
A <%= exception.class.to_s %> occured: <%= exception.to_s %>
<% if body = extract_body(env) %>

===================================================================
Request Body:
===================================================================

<%= body.gsub(/^/, ' ') %>
<% end %>

===================================================================
Rack Environment:
===================================================================

PID: <%= $$ %>
PWD: <%= Dir.getwd %>

<%= env.to_a.
sort{|a,b| a.first <=> b.first}.
map{ |k,v| "%-25s%p" % [k+':', v] }.
join("\n ") %>

<% if exception.respond_to?(:backtrace) %>
===================================================================
Backtrace:
===================================================================

<%= exception.backtrace.join("\n ") %>
<% end %>
EMAIL

  end
end
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