fix(otel): fix otel sampling mode lua panic bug when http_response_header_for_traceid option enable

changelog/unreleased/kong/otel-sampling-panic-when-header-trace-id-enable.yml

@@ -0,0 +1,3 @@
+message: "**Opentelemetry**: fix otel sampling mode lua panic bug when http_response_header_for_traceid option enable"
+type: bugfix
+scope: Plugin

kong/plugins/opentelemetry/handler.lua

@@ -158,8 +158,10 @@ function OpenTelemetryHandler:header_filter(conf)
       local root_span = ngx.ctx.KONG_SPANS and ngx.ctx.KONG_SPANS[1]
       trace_id = root_span and root_span.trace_id
     end
-    trace_id = to_hex(trace_id)
-    kong.response.add_header(conf.http_response_header_for_traceid, trace_id)
+    if trace_id then
+      trace_id = to_hex(trace_id)
+      kong.response.add_header(conf.http_response_header_for_traceid, trace_id)
+    end
   end
 end
 

spec/03-plugins/37-opentelemetry/05-otelcol_spec.lua

@@ -120,6 +120,34 @@ for _, strategy in helpers.each_strategy() do
           return #parts > 0
         end, 10)
       end)
+
+      it("send traces with config http_response_header_for_traceid enable and tracing_sampling_rate option", function()
+        assert(helpers.restart_kong {
+          database = strategy,
+          nginx_conf = "spec/fixtures/custom_nginx.template",
+          plugins = "opentelemetry",
+          tracing_instrumentations = "all",
+          tracing_sampling_rate = 0.00005,
+        })
+
+        proxy_url = fmt("http://%s:%s", helpers.get_proxy_ip(), helpers.get_proxy_port())
+        proxy_url_enable_traceid = fmt("http://%s:%s/enable_response_header_traceid", helpers.get_proxy_ip(), helpers.get_proxy_port())
+
+        local httpc = http.new()
+        for i = 1, 100 do
+          local res, err = httpc:request_uri(proxy_url_enable_traceid)
+          assert.is_nil(err)
+          assert.same(200, res.status)
+          if res.headers["x-trace-id"] then
+            local trace_id = res.headers["x-trace-id"]
+            local trace_id_regex = [[^[a-f0-9]{32}$]]
+            local m = ngx.re.match(trace_id, trace_id_regex, "jo")
+            assert.True(m ~= nil, "trace_id does not match regex: " .. trace_id_regex)
+          end
+        end
+        httpc:close()
+      end)
+
     end)
 
   end)