Add X-OpenFaaS-Internal header for concurrency limiting

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <[email protected]>

concurrency-limiter/concurrency_limiter.go

@@ -72,6 +72,7 @@ func (cl *ConcurrencyLimiter) ServeHTTP(w http.ResponseWriter, r *http.Request)
 		// Some APIs only return JSON, since we can interfere here and send a plain/text
 		// message, let's do the right thing so that downstream users can consume it.
 		w.Header().Add("Content-Type", "text/plain")
+		w.Header().Add("X-OpenFaaS-Internal", "faas-middleware")
 
 		w.WriteHeader(http.StatusTooManyRequests)
 

concurrency-limiter/concurrency_limiter_test.go

@@ -260,6 +260,7 @@ func TestConcurrencyLimitOverLimit(t *testing.T) {
 
 	want := "text/plain"
 	gotContentType := 0
+	gotInternalHeader := 0
 	if rr1.Header().Get("Content-Type") == want {
 		gotContentType++
 	}
@@ -270,10 +271,23 @@ func TestConcurrencyLimitOverLimit(t *testing.T) {
 		gotContentType++
 	}
 
+	if rr1.Header().Get("X-OpenFaaS-Internal") == "faas-middleware" {
+		gotInternalHeader++
+	}
+	if rr2.Header().Get("X-OpenFaaS-Internal") == "faas-middleware" {
+		gotInternalHeader++
+	}
+	if rr3.Header().Get("X-OpenFaaS-Internal") == "faas-middleware" {
+		gotInternalHeader++
+	}
+
 	if gotContentType == 0 {
 		t.Fatalf("Want at least one request with Content-Type %q, got: %q %q %q", want, rr1.Header().Get("Content-Type"), rr2.Header().Get("Content-Type"), rr3.Header().Get("Content-Type"))
 	}
 
+	if gotInternalHeader == 0 {
+		t.Fatalf("Want at least one request with X-OpenFaaS-Internal header, got: %q %q %q", rr1.Header().Get("X-OpenFaaS-Internal"), rr2.Header().Get("X-OpenFaaS-Internal"), rr3.Header().Get("X-OpenFaaS-Internal"))
+	}
 }
 
 func TestConcurrencyLimitOverLimitAndRecover(t *testing.T) {

go.mod

@@ -1,3 +1,3 @@
 module github.com/openfaas/faas-middleware
 
-go 1.18
+go 1.20