fix(opentelemetry): tostring header_type avoid concatenation nil error in log

changelog/unreleased/kong-ee/fix-opentelemetry-header-type-is-null.yml

@@ -0,0 +1,3 @@
+message: "**OpenTelemetry**: Fixed an issue where header_type being nil caused a concatenation error."
+type: bugfix
+scope: Plugin

kong/tracing/propagation.lua

@@ -583,7 +583,7 @@ local function set(conf_header_type, found_header_type, proxy_span, conf_default
      found_header_type ~= nil and
      conf_header_type ~= found_header_type
   then
-    kong.log.warn("Mismatched header types. conf: " .. conf_header_type .. ". found: " .. found_header_type)
+    kong.log.warn("Mismatched header types. conf: " .. tostring(conf_header_type) .. ". found: " .. found_header_type)
   end
 
   found_header_type = found_header_type or conf_default_header_type or "b3"

spec/03-plugins/37-opentelemetry/03-propagation_spec.lua

@@ -71,6 +71,11 @@ describe("propagation tests #" .. strategy, function()
       service = service,
     })
 
+    local null_header_type_route = bp.routes:insert({
+      hosts = { "null-header-type" },
+      service = service,
+    })
+
     bp.plugins:insert({
       name = "opentelemetry",
       route = {id = bp.routes:insert({
@@ -123,6 +128,15 @@ describe("propagation tests #" .. strategy, function()
       }
     })
 
+    bp.plugins:insert({
+      name = "opentelemetry",
+      route = null_header_type_route,
+      config = {
+        endpoint = "http://localhost:8080/v1/traces",
+        header_type = require("cjson").null,
+      }
+    })
+
     helpers.start_kong({
       database = strategy,
       plugins = "bundled, trace-propagator",
@@ -258,6 +272,20 @@ describe("propagation tests #" .. strategy, function()
     assert.not_matches("00%-" .. trace_id .. "%-%x+-01", json.headers.traceparent)
   end)
 
+  it("null_header_type", function()
+    local trace_id = gen_trace_id()
+    local r = proxy_client:get("/", {
+      headers = {
+        ["x-b3-sampled"] = "1",
+        ["x-b3-traceid"] = trace_id,
+        host  = "null-header-type",
+      },
+    })
+    local body = assert.response(r).has.status(200)
+    local json = cjson.decode(body)
+    assert.is_nil(json.headers.traceparent)
+  end)
+
   it("propagates w3c tracing headers when header_type set to w3c", function()
     local trace_id = gen_trace_id()
     local parent_id = gen_span_id()