class OpenTelemetry::Adapters::Rack::Middlewares::TracerMiddleware

TracerMiddleware propagates context and instruments Rack requests by way of its middleware system

Constants

EMPTY_HASH

Public Class Methods

allowed_rack_request_headers() click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 19
def allowed_rack_request_headers
  @allowed_rack_request_headers ||= Array(config[:allowed_request_headers]).each_with_object({}) do |header, memo|
    memo["HTTP_#{header.to_s.upcase.gsub(/[-\s]/, '_')}"] = build_attribute_name('http.request.headers.', header)
  end
end
allowed_response_headers() click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 25
def allowed_response_headers
  @allowed_response_headers ||= Array(config[:allowed_response_headers]).each_with_object({}) do |header, memo|
    memo[header] = build_attribute_name('http.response.headers.', header)
    memo[header.to_s.upcase] = build_attribute_name('http.response.headers.', header)
  end
end
build_attribute_name(prefix, suffix) click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 32
def build_attribute_name(prefix, suffix)
  prefix + suffix.to_s.downcase.gsub(/[-\s]/, '_')
end
config() click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 36
def config
  Rack::Adapter.instance.config
end
new(app) click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 50
def initialize(app)
  @app = app
end

Private Class Methods

clear_cached_config() click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 42
def clear_cached_config
  @allowed_rack_request_headers = nil
  @allowed_response_headers = nil
end

Public Instance Methods

call(env) click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 54
def call(env)
  original_env = env.dup
  extracted_context = OpenTelemetry.propagation.http.extract(env)
  frontend_context = create_frontend_span(env, extracted_context)

  # restore extracted context in this process:
  OpenTelemetry::Context.with_current(frontend_context || extracted_context) do
    request_span_name = create_request_span_name(env['REQUEST_URI'] || original_env['PATH_INFO'])
    request_span_kind = frontend_context.nil? ? :server : :internal
    tracer.in_span(request_span_name,
                   attributes: request_span_attributes(env: env),
                   kind: request_span_kind) do |request_span|
      @app.call(env).tap do |status, headers, response|
        set_attributes_after_request(request_span, status, headers, response)
      end
    end
  end
ensure
  finish_span(frontend_context)
end

Private Instance Methods

allowed_request_headers(env) click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 153
def allowed_request_headers(env)
  return EMPTY_HASH if self.class.allowed_rack_request_headers.empty?

  {}.tap do |result|
    self.class.allowed_rack_request_headers.each do |key, value|
      result[value] = env[key] if env.key?(key)
    end
  end
end
allowed_response_headers(headers) click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 163
def allowed_response_headers(headers)
  return EMPTY_HASH if headers.nil?
  return EMPTY_HASH if self.class.allowed_response_headers.empty?

  {}.tap do |result|
    self.class.allowed_response_headers.each do |key, value|
      if headers.key?(key)
        result[value] = headers[key]
      else
        # do case-insensitive match:
        headers.each do |k, v|
          if k.upcase == key
            result[value] = v
            break
          end
        end
      end
    end
  end
end
config() click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 184
def config
  Rack::Adapter.instance.config
end
create_frontend_span(env, extracted_context) click to toggle source

return Context with the frontend span as the current span

# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 78
def create_frontend_span(env, extracted_context)
  request_start_time = OpenTelemetry::Adapters::Rack::Util::QueueTime.get_request_start(env)

  return unless config[:record_frontend_span] && !request_start_time.nil?

  span = tracer.start_span('http_server.proxy',
                           with_parent_context: extracted_context,
                           attributes: {
                             'component' => 'http',
                             'start_time' => request_start_time.to_f
                           },
                           kind: :server)

  extracted_context.set_value(current_span_key, span)
end
create_request_span_name(request_uri_or_path_info) click to toggle source

github.com/open-telemetry/opentelemetry-specification/blob/master/specification/data-http.md#name

recommendation: span.name(s) should be low-cardinality (e.g., strip off query param value, keep param name)

see github.com/open-telemetry/opentelemetry-specification/pull/416/files

# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 130
def create_request_span_name(request_uri_or_path_info)
  # NOTE: dd-trace-rb has implemented 'quantization' (which lowers url cardinality)
  #       see Datadog::Quantization::HTTP.url

  if (implementation = config[:url_quantization])
    implementation.call(request_uri_or_path_info)
  else
    request_uri_or_path_info
  end
end
current_span_key() click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 98
def current_span_key
  OpenTelemetry::Trace::Propagation::ContextKeys.current_span_key
end
finish_span(context) click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 94
def finish_span(context)
  context[current_span_key]&.finish if context
end
fullpath(env) click to toggle source

e.g., “/webshop/articles/4?s=1”:

# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 117
def fullpath(env)
  query_string = env['QUERY_STRING']
  path = env['SCRIPT_NAME'] + env['PATH_INFO']

  query_string.empty? ? path : "#{path}?#{query_string}"
end
request_span_attributes(env:) click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 106
def request_span_attributes(env:)
  {
    'component' => 'http',
    'http.method' => env['REQUEST_METHOD'],
    'http.host' => env['HTTP_HOST'] || 'unknown',
    'http.scheme' => env['rack.url_scheme'],
    'http.target' => fullpath(env)
  }.merge(allowed_request_headers(env))
end
set_attributes_after_request(span, status, headers, _response) click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 141
def set_attributes_after_request(span, status, headers, _response)
  span.status = OpenTelemetry::Trace::Status.http_to_status(status)
  span.set_attribute('http.status_code', status)

  # NOTE: if data is available, it would be good to do this:
  # set_attribute('http.route', ...
  # e.g., "/users/:userID?
  span.set_attribute('http.status_text', ::Rack::Utils::HTTP_STATUS_CODES[status])

  allowed_response_headers(headers).each { |k, v| span.set_attribute(k, v) }
end
tracer() click to toggle source
# File lib/opentelemetry/adapters/rack/middlewares/tracer_middleware.rb, line 102
def tracer
  OpenTelemetry::Adapters::Rack::Adapter.instance.tracer
end