Class: OpenCensus::Trace::Integrations::RackMiddleware

Inherits:
Object
  • Object
show all
Defined in:
lib/opencensus/trace/integrations/rack_middleware.rb

Overview

# Rack integration

This is a middleware for Rack applications:

  • It wraps all incoming requests in a root span

  • It exports the captured spans at the end of the request.

Example:

require "opencensus/trace/integrations/rack_middleware"

use OpenCensus::Trace::Integrations::RackMiddleware

Constant Summary collapse

AUTODETECTABLE_FORMATTERS =

List of trace context formatters we use to parse the parent span context.

[
  Formatters::CloudTrace.new,
  Formatters::TraceContext.new
].freeze

Instance Method Summary collapse

Constructor Details

#initialize(app, exporter: nil) ⇒ RackMiddleware

Create the Rack middleware.

Parameters:

  • app (#call) —

    Next item on the middleware stack

  • exporter (#export) (defaults to: nil) —

    The exported used to export captured spans at the end of the request. Optional: If omitted, uses the exporter in the current config.



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# File 'lib/opencensus/trace/integrations/rack_middleware.rb', line 54

def initialize app, exporter: nil
  @app = app
  @exporter = exporter || OpenCensus::Trace.config.exporter
end

Instance Method Details

#call(env) ⇒ Array

Run the Rack middleware.

Parameters:

  • env (Hash) —

    The rack environment

Returns:

  • (Array) —

    The rack response. An array with 3 elements: the HTTP response code, a Hash of the response headers, and the response body which must respond to ‘each`.



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# File 'lib/opencensus/trace/integrations/rack_middleware.rb', line 67

def call env
  formatter = AUTODETECTABLE_FORMATTERS.detect do |f|
    env.key? f.rack_header_name
  end
  if formatter
    context = formatter.deserialize env[formatter.rack_header_name]
  end

  Trace.start_request_trace \
    trace_context: context,
    same_process_as_parent: false do |span_context|
    begin
      span_context.in_span get_path(env) do |span|
        start_request span, env
        @app.call(env).tap do |response|
          finish_request span, response
        end
      end
    ensure
      @exporter.export span_context.build_contained_spans
    end
  end
end