This time actually use the path group in the resource name

This is fixing up the previous commit, because upon closer inspection it
turns out that there is no path_group tag on these spans, because that
tag is generated later on in the Datadog Agent. We can generate this tag
ourselves though, at least roughly, so this should fix the issue.

lib/degica_datadog/tracing.rb

@@ -4,10 +4,10 @@
 
 module DegicaDatadog
   # Tracing related functionality.
-  module Tracing
+  module Tracing # rubocop:disable Metrics/ModuleLength
     class << self
       # Initialize Datadog tracing. Call this in from config/application.rb.
-      def init(rake_tasks: []) # rubocop:disable Metrics/AbcSize,Metrics/MethodLength
+      def init(rake_tasks: []) # rubocop:disable Metrics/AbcSize,Metrics/MethodLength,Metrics/CyclomaticComplexity,Metrics/PerceivedComplexity
         return unless Config.enabled?
 
         require "ddtrace/auto_instrument"
@@ -63,7 +63,17 @@ def init(rake_tasks: []) # rubocop:disable Metrics/AbcSize,Metrics/MethodLength
           # Use method + path as the resource name for outbound HTTP requests.
           Datadog::Tracing::Pipeline::SpanProcessor.new do |span|
             if %w[ethon faraday net/http httpclient httprb].include?(span.get_tag("component"))
-              span.resource = "#{span.get_tag("http.method")} #{span.get_tag("http.path_group")}"
+              # The path group is normally generated in the agent, later on. We
+              # don't want to use the raw path in the resource name, as that
+              # would create a lot of resources for any path that contains an
+              # ID. The logic seems to be at least vaguely to replace any path
+              # segment that contains a digit with a ?, so we're reproducing
+              # that here.
+              path_group = span.get_tag("http.path")
+                .split("/")
+                .map { |segment| segment =~ /\d/ ? "?" : segment }
+                .join("/")
+              span.resource = "#{span.get_tag("http.method")} #{path_group}"
             end
           end
         )