feat(performance): don't record HTTP OPTIONS and HEAD transactions

Author: natikgadzhi

CHANGELOG.md

@@ -19,6 +19,7 @@
     ```rb
     config.enabled_patches += [:sidekiq_scheduler]
     ```
+- Sentry will not record traces of HTTP OPTIONS and HEAD requests in Rack and Rails apps [#2181](https://github.com/getsentry/sentry-ruby/pull/2181)
 
 ### Bug Fixes
 

sentry-ruby/lib/sentry/rack/capture_exceptions.rb

@@ -4,6 +4,7 @@ module Sentry
   module Rack
     class CaptureExceptions
       ERROR_EVENT_ID_KEY = "sentry.error_event_id"
+      IGNORED_HTTP_METHODS = ["HEAD", "OPTIONS"].freeze
 
       def initialize(app)
         @app = app
@@ -62,7 +63,17 @@ def capture_exception(exception, env)
       end
 
       def start_transaction(env, scope)
-        options = { name: scope.transaction_name, source: scope.transaction_source, op: transaction_op }
+        options = {
+          name: scope.transaction_name,
+          source: scope.transaction_source, 
+          op: transaction_op
+        }
+        
+        # Tell Sentry to not sample this transaction if this is an HTTP OPTIONS or HEAD request.
+        if IGNORED_HTTP_METHODS.include?(env["REQUEST_METHOD"])
+          options.merge!(sampled: false)
+        end
+
         transaction = Sentry.continue_trace(env, **options)
         Sentry.start_transaction(transaction: transaction, custom_sampling_context: { env: env }, **options)
       end

sentry-ruby/lib/sentry/transaction.rb

@@ -188,6 +188,8 @@ def set_initial_sample_decision(sampling_context:)
         return
       end
 
+      # This block would return either true / false (if parent was sampled or not)
+      # or the sample rate from the configuration, presumably between 0 and 1.
       sample_rate =
         if @traces_sampler.is_a?(Proc)
           @traces_sampler.call(sampling_context)

sentry-ruby/spec/sentry/rack/capture_exceptions_spec.rb

@@ -178,6 +178,7 @@ def inspect
         expect(event.breadcrumbs.count).to eq(1)
         expect(event.breadcrumbs.peek.message).to eq("request breadcrumb")
       end
+
       it "doesn't pollute the top-level scope" do
         request_1 = lambda do |e|
           Sentry.configure_scope { |s| s.set_tags({tag_1: "foo"}) }
@@ -192,6 +193,7 @@ def inspect
         expect(event.tags).to eq(tag_1: "foo")
         expect(Sentry.get_current_scope.tags).to eq(tag_1: "don't change me")
       end
+
       it "doesn't pollute other request's scope" do
         request_1 = lambda do |e|
           Sentry.configure_scope { |s| s.set_tags({tag_1: "foo"}) }