fix: Do not overwrite baggage header contents if it already exists (#2896)

Author: jakubsomonday

CHANGELOG.md

@@ -8,6 +8,7 @@
 
 ### Bug Fixes 🐛
 
+- Do not overwrite baggage header contents if it already exists by @jakubsomonday in [#2894](https://github.com/getsentry/sentry-ruby/pull/2894)
 - (rails) Set mechanism.handled based on error handling status by @solnic in [#2892](https://github.com/getsentry/sentry-ruby/pull/2892)
 - Copy event processors on Scope#dup by @sl0thentr0py in [#2893](https://github.com/getsentry/sentry-ruby/pull/2893)
 - Map `trilogy` database adapter to `mysql` for Query Insights compatibility by @krismichalski in [#2656](https://github.com/getsentry/sentry-ruby/pull/2656)

sentry-ruby/lib/sentry/utils/http_tracing.rb

@@ -12,7 +12,13 @@ def set_span_info(sentry_span, request_info, response_status)
       end
 
       def set_propagation_headers(req)
-        Sentry.get_trace_propagation_headers&.each { |k, v| req[k] = v }
+        Sentry.get_trace_propagation_headers&.each do |k, v|
+          if k == BAGGAGE_HEADER_NAME && req[k]
+            req[k] = "#{v},#{req[k]}"
+          else
+            req[k] = v
+          end
+        end
       end
 
       def record_sentry_breadcrumb(request_info, response_status)

sentry-ruby/spec/sentry/net/http_spec.rb

@@ -192,6 +192,45 @@
       )
     end
 
+    it "merges baggage header with pre-existing baggage on the request" do
+      stub_normal_response
+
+      uri = URI("http://example.com/path")
+      http = Net::HTTP.new(uri.host, uri.port)
+      request = Net::HTTP::Get.new(uri.request_uri)
+      request["baggage"] = "routingKey=myvalue,tenantId=123"
+
+      transaction = Sentry.start_transaction
+      Sentry.get_current_scope.set_span(transaction)
+
+      response = http.request(request)
+
+      expect(response.code).to eq("200")
+      request_span = transaction.span_recorder.spans.last
+      sentry_baggage = request_span.to_baggage
+
+      expect(request["baggage"]).to include(sentry_baggage)
+      expect(request["baggage"]).to include("routingKey=myvalue,tenantId=123")
+      expect(request["baggage"]).to eq("#{sentry_baggage},routingKey=myvalue,tenantId=123")
+    end
+
+    it "sets baggage header normally when no pre-existing baggage on the request" do
+      stub_normal_response
+
+      uri = URI("http://example.com/path")
+      http = Net::HTTP.new(uri.host, uri.port)
+      request = Net::HTTP::Get.new(uri.request_uri)
+
+      transaction = Sentry.start_transaction
+      Sentry.get_current_scope.set_span(transaction)
+
+      response = http.request(request)
+
+      expect(response.code).to eq("200")
+      request_span = transaction.span_recorder.spans.last
+      expect(request["baggage"]).to eq(request_span.to_baggage)
+    end
+
     context "with config.propagate_traces = false" do
       before do
         Sentry.configuration.propagate_traces = false