Respond to empty RPC requests with HTTP OK status

When receiving an HTTP GET request with no content and no URL query,
we assume the client may be a health check probe, and process the
request without complaint. We had been omitting the HTTP status code
in our otherwise empty response, though, which aggravates some HTTP
clients. Instead, respond with HTTP status code 200, indicating the
request was accepted and processed successfully.

rpc/http.go

@@ -208,6 +208,7 @@ func (t *httpServerConn) SetWriteDeadline(time.Time) error { return nil }
 func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	// Permit dumb empty requests for remote health-checks (AWS)
 	if r.Method == http.MethodGet && r.ContentLength == 0 && r.URL.RawQuery == "" {
+		w.WriteHeader(http.StatusOK)
 		return
 	}
 	if code, err := validateRequest(r); err != nil {

rpc/http_test.go

@@ -23,32 +23,78 @@ import (
 	"testing"
 )
 
+func confirmStatusCode(t *testing.T, got, want int) {
+	t.Helper()
+	if got == want {
+		return
+	}
+	if gotName := http.StatusText(got); len(gotName) > 0 {
+		if wantName := http.StatusText(want); len(wantName) > 0 {
+			t.Fatalf("response status code: got %d (%s), want %d (%s)", got, gotName, want, wantName)
+		}
+	}
+	t.Fatalf("response status code: got %d, want %d", got, want)
+}
+
+func confirmRequestValidationCode(t *testing.T, method, contentType, body string, expectedStatusCode int) {
+	t.Helper()
+	request := httptest.NewRequest(method, "http://url.com", strings.NewReader(body))
+	if len(contentType) > 0 {
+		request.Header.Set("Content-Type", contentType)
+	}
+	code, err := validateRequest(request)
+	if code == 0 {
+		if err != nil {
+			t.Errorf("validation: got error %v, expected nil", err)
+		}
+	} else if err == nil {
+		t.Errorf("validation: code %d: got nil, expected error", code)
+	}
+	confirmStatusCode(t, code, expectedStatusCode)
+}
+
 func TestHTTPErrorResponseWithDelete(t *testing.T) {
-	testHTTPErrorResponse(t, http.MethodDelete, contentType, "", http.StatusMethodNotAllowed)
+	confirmRequestValidationCode(t, http.MethodDelete, contentType, "", http.StatusMethodNotAllowed)
 }
 
 func TestHTTPErrorResponseWithPut(t *testing.T) {
-	testHTTPErrorResponse(t, http.MethodPut, contentType, "", http.StatusMethodNotAllowed)
+	confirmRequestValidationCode(t, http.MethodPut, contentType, "", http.StatusMethodNotAllowed)
 }
 
 func TestHTTPErrorResponseWithMaxContentLength(t *testing.T) {
 	body := make([]rune, maxRequestContentLength+1)
-	testHTTPErrorResponse(t,
+	confirmRequestValidationCode(t,
 		http.MethodPost, contentType, string(body), http.StatusRequestEntityTooLarge)
 }
 
 func TestHTTPErrorResponseWithEmptyContentType(t *testing.T) {
-	testHTTPErrorResponse(t, http.MethodPost, "", "", http.StatusUnsupportedMediaType)
+	confirmRequestValidationCode(t, http.MethodPost, "", "", http.StatusUnsupportedMediaType)
 }
 
 func TestHTTPErrorResponseWithValidRequest(t *testing.T) {
-	testHTTPErrorResponse(t, http.MethodPost, contentType, "", 0)
+	confirmRequestValidationCode(t, http.MethodPost, contentType, "", 0)
 }
 
-func testHTTPErrorResponse(t *testing.T, method, contentType, body string, expected int) {
-	request := httptest.NewRequest(method, "http://url.com", strings.NewReader(body))
-	request.Header.Set("content-type", contentType)
-	if code, _ := validateRequest(request); code != expected {
-		t.Fatalf("response code should be %d not %d", expected, code)
+func confirmHTTPRequestYieldsStatusCode(t *testing.T, method, contentType, body string, expectedStatusCode int) {
+	t.Helper()
+	s := Server{}
+	ts := httptest.NewServer(&s)
+	defer ts.Close()
+
+	request, err := http.NewRequest(method, ts.URL, strings.NewReader(body))
+	if err != nil {
+		t.Fatalf("failed to create a valid HTTP request: %v", err)
 	}
+	if len(contentType) > 0 {
+		request.Header.Set("Content-Type", contentType)
+	}
+	resp, err := http.DefaultClient.Do(request)
+	if err != nil {
+		t.Fatalf("request failed: %v", err)
+	}
+	confirmStatusCode(t, resp.StatusCode, expectedStatusCode)
+}
+
+func TestHTTPResponseWithEmptyGet(t *testing.T) {
+	confirmHTTPRequestYieldsStatusCode(t, http.MethodGet, "", "", http.StatusOK)
 }