Class: LaunchDarklyObservability::Middleware

Inherits:
Object
  • Object
show all
Defined in:
lib/launchdarkly_observability/middleware.rb

Overview

Rack middleware for request tracing

This middleware wraps incoming HTTP requests in OpenTelemetry spans, providing context for flag evaluations that occur during request processing.

Works with any Rack-compatible framework (Rails, Sinatra, Grape, Hanami, etc.). In Rails, the Railtie inserts this middleware automatically. For other frameworks, add it manually to your middleware stack:

Examples:

Sinatra

use LaunchDarklyObservability::Middleware

Rack::Builder

use LaunchDarklyObservability::Middleware
run MyApp

Constant Summary collapse

OBSERVABILITY_REQUEST_HEADER =

Header for observability request context (session/request ID propagation)

'HTTP_X_HIGHLIGHT_REQUEST'
SESSION_BAGGAGE_KEY =

Baggage keys for context propagation

'launchdarkly.session_id'
REQUEST_BAGGAGE_KEY = 
'launchdarkly.request_id'

Instance Method Summary collapse

Constructor Details

#initialize(app) ⇒ Middleware

Returns a new instance of Middleware.



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# File 'lib/launchdarkly_observability/middleware.rb', line 28

def initialize(app)
  @app = app
end

Instance Method Details

#call(env) ⇒ Array

Process the request with tracing context

Parameters:

  • env (Hash) —

    Rack environment

Returns:

  • (Array) —

    Rack response tuple



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# File 'lib/launchdarkly_observability/middleware.rb', line 36

def call(env)
  return @app.call(env) unless tracing_available?

  request = Rack::Request.new(env)
  session_id, request_id = extract_observability_context(env)
  ctx = set_baggage_context(session_id, request_id)
  app_error = nil

  OpenTelemetry::Context.with_current(ctx) do
    tracer.in_span(span_name(request), attributes: request_attributes(request)) do |span|
      span.set_attribute(SESSION_BAGGAGE_KEY, session_id) if session_id
      span.set_attribute(REQUEST_BAGGAGE_KEY, request_id) if request_id

      begin
        status, headers, body = @app.call(env)
      rescue StandardError => e
        app_error = e
        span.record_exception(e, attributes: SourceContext.exception_attributes(e))
        span.status = OpenTelemetry::Trace::Status.error(e.message)
        raise
      end

      span.set_attribute('http.status_code', status)
      span.status = OpenTelemetry::Trace::Status.error("HTTP #{status}") if status >= 500
      [status, headers, body]
    end
  end
rescue StandardError => e
  raise if app_error

  warn "[LaunchDarklyObservability] Middleware error: #{e.message}"
  @app.call(env)
end