Improve lambda<->rack interface adherence to Rack's SPEC.

* HTTP header names must be capitalized. * `CONTENT_TYPE` and `CONTENT_LENGTH` lack `HTTP_` prefix. * Don't hard-code server name, port, or scheme, when they are available from the Lambda event.

Author: aarontc

lambda.rb

@@ -20,40 +20,52 @@
 # Global object that responds to the call method. Stay outside of the handler
 # to take advantage of container reuse
 $app ||= Rack::Builder.parse_file("#{__dir__}/app/config.ru").first
+ENV['RACK_ENV'] ||= 'production'
 
-def handler(event:, context:)
+
+def lambda_handler(event:, context:)
  # Check if the body is base64 encoded. If it is, try to decode it
- body = 
- if event['isBase64Encoded']
-  Base64.decode64(event['body'])
- else
-  event['body']
- end
+ body = if event['isBase64Encoded']
+ Base64.decode64 event['body']
+ else
+ event['body']
+ end || ''
+
  # Rack expects the querystring in plain text, not a hash
- querystring = Rack::Utils.build_query(event['queryStringParameters']) if event['queryStringParameters']
+ headers = event.fetch 'headers', {}
+
  # Environment required by Rack (http://www.rubydoc.info/github/rack/rack/file/SPEC)
  env = {
- 'REQUEST_METHOD' => event['httpMethod'],
+ 'REQUEST_METHOD' => event.fetch('httpMethod'),
  'SCRIPT_NAME' => '',
- 'PATH_INFO' => event['path'] || '',
- 'QUERY_STRING' => querystring || '',
- 'SERVER_NAME' => 'localhost',
- 'SERVER_PORT' => 443,
- 'CONTENT_TYPE' => event['headers']['content-type'],
+ 'PATH_INFO' => event.fetch('path', ''),
+ 'QUERY_STRING' => Rack::Utils.build_query(event['queryStringParameters'] || {}),
+ 'SERVER_NAME' => headers.fetch('Host', 'localhost'),
+ 'SERVER_PORT' => headers.fetch('X-Forwarded-Port', 443).to_s,
 
  'rack.version' => Rack::VERSION,
- 'rack.url_scheme' => 'https',
- 'rack.input' => StringIO.new(body || ''),
+ 'rack.url_scheme' => headers.fetch('CloudFront-Forwarded-Proto') { headers.fetch('X-Forwarded-Proto', 'https') },
+ 'rack.input' => StringIO.new(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 }
+ headers.each_pair do |key, value|
+ # 'CloudFront-Forwarded-Proto' => 'CLOUDFRONT_FORWARDED_PROTO'
+ # Content-Type and Content-Length are handled specially per the Rack SPEC linked above.
+ name = key.upcase.gsub '-', '_'
+ header = case name
+ when 'CONTENT_TYPE', 'CONTENT_LENGTH'
+ name
+ else
+ "HTTP_#{name}"
+ end
+ env[header] = value.to_s
  end
 
  begin
  # Response from Rack must have status, headers and body
- status, headers, body = $app.call(env)
+ status, headers, body = $app.call env
 
  # body is an array. We combine all the items to a single string
  body_content = ""
@@ -68,17 +80,18 @@ def handler(event:, context:)
  'headers' => headers,
  'body' => body_content
  }
- if event['requestContext'].key?('elb')
+ if event['requestContext'].has_key?('elb')
  # Required if we use Application Load Balancer instead of API Gateway
  response['isBase64Encoded'] = false
  end
- rescue Exception => msg
- # If there is any exception, we return a 500 error with an error message
+ rescue Exception => exception
+ # If there is _any_ exception, we return a 500 error with an error message
  response = {
  'statusCode' => 500,
- 'body' => msg
+ 'body' => exception.message
  }
  end
+
  # By default, the response serializer will call #to_json for us
  response
 end