Example of how to use the post-to-s3 ruby on rails gem

new.html.erb

<h1>Upload Your File</h1>

<%= s3_upload_form_for(@upload) do %>
  <p><%= label_tag :file, 'Select Your File' %></p>
  <p><%= file_field_tag :file  %></p>
<% end %>

s3-bucket-policy.json

{
  "disclaimer": "This is just an example and may not work for your S3 setup.",
  "Sid": "Stmt1328506705529",
  "Effect": "Allow",
  "Principal": {
    "AWS": "arn:aws:iam::395340211253:root"
  },
  "Action": [
    "s3:PutObject"
  ],
  "Resource": "arn:aws:s3:::mywebsite-media/uploads/*"
}

s3.yml

# This is a configuration file in config/

development:
  bucket_name: <your bucket name>
  access_key_id: <your access key>
  secret_access_key: <your secret key>

test:
  bucket_name: <your bucket name>
  access_key_id: <your access key>
  secret_access_key: <your secret key>

production:
  bucket_name: <your bucket name>
  access_key_id: <your access key>
  secret_access_key: <your secret key>

settings.rb

# This is an initializer in config/initializers/, however, storing your S3 keys in a file that you check in might not be the best idea. This is mostly to show how to explicitly set the values. 
# PostToS3 defaults to checking for  AMAZON_ACCESS_KEY_ID and AMAZON_SECRET_ACCESS_KEY environment variables. If you set them that way, you can omit the keys from this configuration process.

APP_CONFIG = {}
APP_CONFIG[:s3] = YAML.load_file("#{Rails.root}/config/s3.yml")[Rails.env.to_s].symbolize_keys!

PostToS3.configure do |config|
  config.access_key_id = APP_CONFIG[:s3][:access_key_id]
  config.access_key_id = APP_CONFIG[:s3][:secret_access_key]
end

uploads_controller.rb

class UploadsController < ApplicationController
  def new
    # Define whatever path you want the upload to have here.
    key = "uploads/#{Time.now.strftime('%Y%m%d%H%M%S')}"

    @upload = PostToS3::FileUpload.new(
      :bucket_url => "http://#{APP_CONFIG[:s3][:bucket_name]}.s3.amazonaws.com/",
      :key => key,
      :policy => {
        'expiration' => 10.hours.from_now,  # Set this to whatever is appropriate
        'conditions' => [
          { 'bucket' => APP_CONFIG[:s3][:bucket_name] },
          { 'key' => key },
          { 'acl' => 'private' }, # Change this if you want it to be public
          { 'success_action_redirect' => '/upload-finished.html' } # Change the URL that you want the user redirected to
        ]
      }
    )
  end
end