Make tasks HTTP URL and Method optional

We changed the design, so now tasks are either executing
a request policy, or an HTTP request to a predefined URL,
but not both.

In the previous commits "request policy" could only be used as
a request transformation and the actual task was executing an
HTTP request to a predefined URL. With the current change tasks
can execute "request policy" if it's set, or make an HTTP call.

internal/executor/worker.go

@@ -64,6 +64,7 @@ func (w *Worker) Start(ctx context.Context) {
 				}
 				continue
 			}
+			logger.Debug("task execution completed successfully")
 
 			if err := w.cache.Set(
 				ctx,
@@ -78,11 +79,13 @@ func (w *Worker) Start(ctx context.Context) {
 				}
 				continue
 			}
+			logger.Debug("task results are stored in cache")
 
 			if err := w.storage.SaveTaskHistory(ctx, executed); err != nil {
 				logger.Error("error saving task history", zap.Error(err))
 				continue
 			}
+			logger.Debug("task history is saved")
 
 			// remove task from queue
 			if err := w.queue.Ack(ctx, executed); err != nil {
@@ -95,23 +98,26 @@ func (w *Worker) Start(ctx context.Context) {
 func (w *Worker) Execute(ctx context.Context, task *taskpkg.Task) (*taskpkg.Task, error) {
 	task.StartedAt = time.Now()
 
-	// evaluate request policy
+	var response []byte
+	var err error
+
+	// task is executing a request policy OR an HTTP call to predefined URL
 	if task.RequestPolicy != "" {
-		resp, err := w.policy.Evaluate(ctx, task.RequestPolicy, task.Request)
+		response, err = w.policy.Evaluate(ctx, task.RequestPolicy, task.Request)
 		if err != nil {
 			return nil, errors.New("error evaluating request policy", err)
 		}
-		// overwrite task request with the one returned from the policy
-		task.Request = resp
-	}
-
-	status, response, err := w.do(ctx, task)
-	if err != nil {
-		return nil, err
+	} else if task.URL != "" && task.Method != "" {
+		var status int
+		status, response, err = w.doHTTPTask(ctx, task)
+		if err != nil {
+			return nil, err
+		}
+		task.ResponseCode = status
+	} else {
+		return nil, errors.New(errors.Internal, "invalid task: must define either request policy or url")
 	}
 
-	task.State = taskpkg.Done
-	task.ResponseCode = status
 	task.Response = response
 
 	// evaluate response policy
@@ -134,11 +140,12 @@ func (w *Worker) Execute(ctx context.Context, task *taskpkg.Task) (*taskpkg.Task
 		task.Response = resp
 	}
 
+	task.State = taskpkg.Done
 	task.FinishedAt = time.Now()
 	return task, nil
 }
 
-func (w *Worker) do(ctx context.Context, task *taskpkg.Task) (status int, response []byte, err error) {
+func (w *Worker) doHTTPTask(ctx context.Context, task *taskpkg.Task) (status int, response []byte, err error) {
 	req, err := http.NewRequest(task.Method, task.URL, bytes.NewReader(task.Request))
 	if err != nil {
 		return 0, nil, errors.New("error creating http request", err)

internal/service/task/task.go

@@ -25,8 +25,8 @@ type Task struct {
 	GroupID        string    `json:"groupID"`        // GroupID is set when the task is part of `task.Group`.
 	Name           string    `json:"name"`           // Name is used by external callers use to create tasks.
 	State          State     `json:"state"`          // State of the task.
-	URL            string    `json:"url"`            // URL against which the task request will be executed.
-	Method         string    `json:"method"`         // HTTP method of the task request.
+	URL            string    `json:"url"`            // URL against which the task request will be executed (optional).
+	Method         string    `json:"method"`         // HTTP method of the task request (optional).
 	Request        []byte    `json:"request"`        // Request body which will be sent in the task request.
 	Response       []byte    `json:"response"`       // Response received after the task request is executed.
 	ResponseCode   int       `json:"responseCode"`   // ResponseCode received after task request is executed.