chore: errors are sent as json

main.go

@@ -41,11 +41,9 @@ func handler(w http.ResponseWriter, r *http.Request) {
 	responseCode, err := validateResponseCode(r.Header)
 	if err != nil {
 		responseBody = err.Error()
-		contentType = "text/plain; charset=utf-8"
 	} else if !isJSON(responseBody) {
-		responseBody = fmt.Errorf("x-response-json must be valid JSON").Error()
+		responseBody = errorResponseFormatter("x-response-json must be valid JSON").Error()
 		responseCode = http.StatusBadRequest
-		contentType = "text/plain; charset=utf-8"
 	}
 
 	w.Header().Set("Content-Type", contentType)
@@ -58,12 +56,12 @@ func validateResponseCode(header map[string][]string) (int, error) {
 		// verify its a number
 		code, err := strconv.Atoi(val[0])
 		if err != nil {
-			return http.StatusBadRequest, fmt.Errorf("x-response-code must be a number\n")
+			return http.StatusBadRequest, errorResponseFormatter("x-response-code must be a number")
 		}
 
 		// verify it falls in the range of status codes
 		if !(code >= 100 && code <= 599) {
-			return http.StatusBadRequest, fmt.Errorf("x-response-code must be between 100 and 599\n")
+			return http.StatusBadRequest, errorResponseFormatter("x-response-code must be between 100 and 599")
 		}
 
 		return code, nil
@@ -77,3 +75,7 @@ func isJSON(s string) bool {
 	var j json.RawMessage
 	return json.Unmarshal([]byte(s), &j) == nil
 }
+
+func errorResponseFormatter(msg string) error {
+	return fmt.Errorf(`{"error":"%s"}`, msg)
+}

main_test.go

@@ -42,9 +42,8 @@ func TestHandlerValidRequest(t *testing.T) {
 }
 
 func TestHandlerWithInvalidXResponseJson(t *testing.T) {
-	expectedContentType := "text/plain; charset=utf-8"
 	invalidResponseBody := `{"foo":bar}`
-	expectedResponseBody := "x-response-json must be valid JSON"
+	expectedResponseBody := `{"error":"x-response-json must be valid JSON"}`
 	expectedResponseCode := http.StatusBadRequest
 
 	// set up the request
@@ -69,16 +68,10 @@ func TestHandlerWithInvalidXResponseJson(t *testing.T) {
 	if rr.Body.String() != expectedResponseBody {
 		t.Errorf("handler returned unexpected body: got '%s' want '%s'", rr.Body.String(), expectedResponseBody)
 	}
-
-	// content-type
-	if rr.Header()["Content-Type"][0] != expectedContentType {
-		t.Errorf("handler returned wrong content-type: got '%s' wanted '%s'", rr.Header()["Content-Type"][0], expectedContentType)
-	}
 }
 
 func TestHandlerWithInvalidXResponseCode(t *testing.T) {
-	expectedContentType := "text/plain; charset=utf-8"
-	expectedResponseBody := "x-response-code must be a number\n"
+	expectedResponseBody := `{"error":"x-response-code must be a number"}`
 	invalidResponseCode := "blah"
 	expectedResponseCode := http.StatusBadRequest
 
@@ -104,11 +97,6 @@ func TestHandlerWithInvalidXResponseCode(t *testing.T) {
 	if rr.Body.String() != expectedResponseBody {
 		t.Errorf("handler returned unexpected body: got '%s' want '%s'", rr.Body.String(), expectedResponseBody)
 	}
-
-	// content-type
-	if rr.Header()["Content-Type"][0] != expectedContentType {
-		t.Errorf("handler returned wrong content-type: got '%s' wanted '%s'", rr.Header()["Content-Type"][0], expectedContentType)
-	}
 }
 
 func TestValidateResponseCode(t *testing.T) {
@@ -145,3 +133,12 @@ func TestIsJSON(t *testing.T) {
 		t.Errorf("expected %s to be invalid JSON\n", invalid)
 	}
 }
+
+func TestErrorResponseFormatter(t *testing.T) {
+	expectedErr := `{"error":"hello"}`
+	err := errorResponseFormatter("hello")
+
+	if err.Error() != expectedErr {
+		t.Errorf("got %s want %s\n", err.Error(), expectedErr)
+	}
+}