lambda.rb

load "vendor/bundle/bundler/setup.rb"
require 'json'
require 'rack'

# Global object that responds to the call method. Stay outside of the handler
# to take advantage of container reuse
$app ||= Rack::Builder.parse_file("#{File.dirname(__FILE__)}/app/config.ru").first

def handler(event:, context:)
  path = (event['path'] || "").gsub(/^\/app/, '')
  puts "Request for: #{path}"

  # Environment required by Rack (http://www.rubydoc.info/github/rack/rack/file/SPEC)
  env = {
    "REQUEST_METHOD" => event['httpMethod'],
    "SCRIPT_NAME" => "",
    "PATH_INFO" => path,
    "QUERY_STRING" => event['queryStringParameters'] || "",
    "SERVER_NAME" => "localhost",
    "SERVER_PORT" => 443,
    
    "rack.version" => Rack::VERSION,
    "rack.url_scheme" => "https",
    "rack.input" => StringIO.new(event['body'] || ""),
    "rack.errors" => $stderr,
  }
  # Pass request headers to Rack if they are available
  unless event['headers'].nil?
    event['headers'].each{ |key, value| env["HTTP_#{key}"] = value }
  end
  
  begin
    # Response from Rack must have status, headers and body
    status, headers, body = $app.call(env)

    # body is an array. We simply combine all the items to a single string
    body_content = ""
    body.each do |item|
      body_content += item.to_s
    end
  
    # We return the structure required by AWS API Gateway since we integrate with it
    # https://docs.aws.amazon.com/apigateway/latest/developerguide/set-up-lambda-proxy-integrations.html
    response = {
      "statusCode" => status,
      "headers" => headers,
      "body" => body_content
    }
  rescue Exception => msg
    # If there is any exception, we return a 500 error with an error message
    response = {
      "statusCode" => 500,
      "body" => msg
    }
  end
  # By default, the response serializer will call #to_json for us
  response
end