invalid %-encoding error in application for malformed uri

comment.md

rack/rack#337 (comment)

Question re: should this be rack's job

# config.ru
run ->(env) {
  [ 200, { 'Content-Type' => 'text/html', }, [Rack::Request.new(env).params.inspect] ]
}

rackup

open http://localhost:9292/?utf8=%E2%9C%93&search=&page=2&commit=%u00ABscript%u00BBalert(209);%u00AB/script%u00BB

ArgumentError at /
invalid %-encoding (%u00ABscript%u00BBalert(209))

Ruby	$HOME/.rvm/rubies/ruby-1.9.3-p484/lib/ruby/1.9.1/uri/common.rb: in decode_www_form_component, line 898
Web	GET localhost/

Would you argue that rackup is not an acceptable app server, then? If not, would you accept a PR to rescue the Argument error in rack, warn that it's the app server's job to fix the issue, and re-raise it?

---

edit: I forgot posted a similar comment in rack/rack#323 (comment)

exception_app.rb

require 'rack'
require 'logger'
class ExceptionApp
  DEFAULT_CONTENT_TYPE = 'text/html'
  DEFAULT_CHARSET      = 'utf-8'

  attr_reader :logger
  def initialize(app, stdout=STDOUT)
    @app = app
    @logger = defined?(Rails.logger) ? Rails.logger : Logger.new(stdout)
  end

  def call(env)
    begin
      # calling env.dup here prevents bad things from happening
      request = Rack::Request.new(env.dup)
      # calling request.params is sufficient to trigger the error
      # see https://github.com/rack/rack/issues/337#issuecomment-46453404
      request.params
      @app.call(env)
    rescue ArgumentError => e
      raise unless e.message =~ /invalid %-encoding/
      message = "BAD REQUEST: Returning 400 due to #{e.message} from request with env #{request.inspect}"
      logger.info message
      content_type = env['HTTP_ACCEPT'] || DEFAULT_CONTENT_TYPE
      status = 400
      body   = "Bad Request"
      return [
        status,
        {
           'Content-Type' => "#{content_type}; charset=#{DEFAULT_CHARSET}",
           'Content-Length' => body.bytesize.to_s
        },
        [body]
      ]
    end
  end

end

exception_app_spec.rb

require_relative 'exception_app'

describe ExceptionApp do

  let(:app) do
    ExceptionApp.new( ->(env){ [418, {}, ["I'm a teapot."]] }, '/dev/null')
  end
  let(:bad_param) { "commit=%u00ABscript%u00BBalert(209);%u00AB/script%u00BB" }
  let(:env) do
    {
      "REQUEST_METHOD"=>"GET",
      "QUERY_STRING"=> bad_param,
      "REQUEST_URI"=>"/?#{bad_param}",
      "PATH_INFO"=>"/",
      "HTTP_ACCEPT"=>"application/json",
      "rack.input" => ""
    }
  end

  it "returns an early 'Bad Request' when given params with a bad encoding" do
    status, headers, body = app.call(env)

    expect(body.join).to eq("Bad Request")
    expect(status).to eq(400)
    expect(headers["Content-Type"]).to eq("application/json; charset=utf-8")
    expect(headers["Content-Length"]).to eq("11")
  end

  it "does nothing when no encoding error if found" do
    status, headers, body = app.call(env.merge("QUERY_STRING" => "", "REQUEST_URI" => "/"))

    expect(body.join).to eq("I'm a teapot.")
    expect(status).to eq(418)
    expect(headers["Content-Type"]).to be_nil
    expect(headers["Content-Length"]).to be_nil
  end

end

@bf4 What are the bad things env.dup prevents from happening?