Rails controller for storing and fetching files from Postgres Large Objects (LO)

postgres_file_storage.rb

require 'digest'

class Api::V2::FileStorageController < ApplicationController
  skip_before_filter :authorize,      :only => [:save, :serve]
  before_filter :authorize_admin_api_token, :only => [:save]

  def save
    if params[:contents].is_a?(ActionDispatch::Http::UploadedFile)
      params[:contents].close(false) # close and don't delete so we can import it
      tmp_file = params[:contents]
    else
      raise "No upload to process."
    end

    uploaded_file = nil
    sha = Digest::SHA512.file tmp_file.path
    sha.hexdigest

    UploadedFile.connection.transaction do
      uploaded_file = UploadedFile.find_or_initialize_by(filename:  params[:filename])

      if uploaded_file && uploaded_file.file_oid
        # Remove old file
        UploadedFile.connection.execute "SELECT LO_UNLINK('#{uploaded_file.file_oid}')"
      end

      res = UploadedFile.connection.execute "SELECT LO_IMPORT('#{tmp_file.path}') AS file_oid"

      uploaded_file.file_oid    = res[0]["file_oid"].to_i
      uploaded_file.checksum    = sha.hexdigest
      uploaded_file.headers     = params[:headers]
      uploaded_file.permissions = params[:permissions] || 'protected'
      
      uploaded_file.save!
    end

    File.unlink tmp_file.path
    render :json => uploaded_file.to_json, status: :created
  end


  def serve
    file = UploadedFile.find_by(filename: params[:filename])
    if file.nil?
      render :text => "File not found.", content_type: "text/plain", status: 404
      return
    end

    if !file.public?
      authorize()
      return unless signed_in?
    end

    # Make sure if file changes that it will bust the cache
    tmp_path = "#{Rails.root}/tmp/uploaded_file_#{file.file_oid}_#{file.updated_at.to_i}"

    if !File.exist?(tmp_path)
      UploadedFile.connection.execute "SELECT LO_EXPORT(#{file.file_oid}, '#{tmp_path}')"
    end

    send_file(tmp_path, type: file.mime_type, disposition: nil)

    file.headers.each do |k, v|
      response.headers[k] = v
    end unless file.headers.nil?
    
  end

end

uploaded_file.rb

class UploadedFile < ActiveRecord::Base
  store_accessor :headers

  def extension
    filename.match(/\.[a-zA-Z]+$/).to_a.first.to_s.downcase
  end

  def mime_type
    Rack::Mime.mime_type(extension)
  end

  def as_json(*args)
    json = super(*args)
    json["mimeType"] = mime_type
    json
  end

  def public?
    permissions == 'public'
  end

end

uploaded_file_migration.rb

class CreateUploadedFiles < ActiveRecord::Migration
  def change
    create_table :uploaded_files do |t|
      t.string  :filename
      t.string  :checksum
      t.string  :permissions
      t.integer :file_oid
      t.hstore  :headers

      t.timestamps
    end
  end
end