These are the necessary changes to add RESTful JSON (and in the process, fix RESTful XML) to the demo on Gist

ReadMe.html

These are the necessary changes to add RESTful JSON (and in the process, fix RESTful XML) to the demo on Gist: <a href="http://gist.github.com/268192">Rails 2.3.5 on App Engine (DataMapper)</a>

They're fairly straightforward, but there's a <a href="http://bit.ly/aOWE0G">write-up here</a>. And the source can be found on the <a href="http://github.com/freshblocks/iPhone-JSON">Github Repository</a>.

config.ru

require 'appengine-rack'
require 'appengine-apis/urlfetch'
require 'cgi'
require 'json'
require 'dm-core'
require 'dm-serializer'

AppEngine::Rack.configure_app(
    :application => 'iphone-json',
    :precompilation_enabled => true,
    :sessions_enabled => true,
    :version => "1")

# original generated code
=begin
AppEngine::Rack.app.resource_files.exclude :rails_excludes
ENV['RAILS_ENV'] = AppEngine::Rack.environment

require ::File.expand_path('../config/environment',  __FILE__)
use Rails::Rack::LogTailer if ENV['RAILS_ENV'].eql? 'development'

run ActionController::Dispatcher.new
=end

# code from jruby-depot.appspot.com
AppEngine::Rack.app.resource_files.exclude :rails_excludes
ENV['RAILS_ENV'] = AppEngine::Rack.environment
 
deferred_dispatcher = AppEngine::Rack::DeferredDispatcher.new(
     :require => File.expand_path('../config/environment', __FILE__),
     :dispatch => 'ActionController::Dispatcher', :isolate => true)
 
map '/admin' do
  use AppEngine::Rack::AdminRequired
  run deferred_dispatcher
end
 
map '/user' do
  use AppEngine::Rack::LoginRequired
  run deferred_dispatcher
end
 
map '/' do
  run deferred_dispatcher
end

contracts_controller.rb

class ContactsController < ApplicationController
  # GET /contacts
  # GET /contacts.xml
  # GET /contacts.json
  def index
    @contacts = Contact.all

    respond_to do |format|
      format.html # index.html.erb
      format.xml  { render :xml => @contacts }
      format.json { render :json => @contacts }
    end
  end

  # GET /contacts/1
  # GET /contacts/1.xml
  # GET /contacts/1.json
  def show
    @contact = Contact.find(params[:id])

    respond_to do |format|
      format.html # show.html.erb
      format.xml  { render :xml => @contact }
      format.json { render :json => @contact }
    end
  end

  # GET /contacts/new
  # GET /contacts/new.xml
  # GET /contacts/new.json
  def new
    @contact = Contact.new

    respond_to do |format|
      format.html # new.html.erb
      format.xml  { render :xml => @contact }
      format.json { render :json => @contact }
    end
  end

  # GET /contacts/1/edit
  def edit
    @contact = Contact.find(params[:id])
  end

  # POST /contacts
  # POST /contacts.xml
  # POST /contacts.json
  def create
    @contact = Contact.new(params[:contact])

    respond_to do |format|
      if @contact.save
        flash[:notice] = 'Contact was successfully created.'
        format.html { redirect_to(@contact) }
        format.xml  { render :xml => @contact, :status => :created, :location => @contact }
        format.json { render :json => @contact, :status => :created, :location => @contact }
      else
        format.html { render :action => "new" }
        format.xml  { render :xml => @contact.errors, :status => :unprocessable_entity }
        format.json { render :json => @contact.errors, :status => :unprocessable_entity }
      end
    end
  end

  # PUT /contacts/1
  # PUT /contacts/1.xml
  # PUT /contacts/1.json
  def update
    @contact = Contact.find(params[:id])

    respond_to do |format|
      if @contact.update_attributes(params[:contact])
        flash[:notice] = 'Contact was successfully updated.'
        format.html { redirect_to(@contact) }
        format.xml  { head :ok }
        format.json { head :ok }
      else
        format.html { render :action => "edit" }
        format.xml  { render :xml => @contact.errors, :status => :unprocessable_entity }
        format.json { render :json => @contact.errors, :status => :unprocessable_entity }
      end
    end
  end

  # DELETE /contacts/1
  # DELETE /contacts/1.xml
  def destroy
    @contact = Contact.find(params[:id])
    @contact.destroy

    respond_to do |format|
      format.html { redirect_to(contacts_url) }
      format.xml  { head :ok }
      format.json { head :ok }
    end
  end
end

Gemfile

# Critical default settings:
disable_system_gems
disable_rubygems
bundle_path '.gems/bundler_gems'

# List gems to bundle here:
gem 'rails_dm_datastore'
gem 'rails', "2.3.5"
gem 'dm-core'
gem "json-jruby"
gem "dm-serializer"