Improve HTTP error handling

internal/server/http.go

@@ -6,7 +6,10 @@ import (
 )
 
 var (
-	ErrNotFound = errors.New("prediction ID not found")
+	ErrExists      = errors.New("prediction exists")
+	ErrNotFound    = errors.New("prediction not found")
+	ErrDefunct     = errors.New("server is defunct")
+	ErrSetupFailed = errors.New("setup failed")
 )
 
 func NewServer(addr string, runner *Runner) *http.Server {

internal/server/runner.go

@@ -192,19 +192,19 @@ func (r *Runner) predict(req PredictionRequest) (chan PredictionResponse, error)
 	log := logger.Sugar()
 	if r.status == StatusSetupFailed {
 		log.Errorw("prediction rejected: setup failed")
-		return nil, fmt.Errorf("setup failed")
+		return nil, ErrSetupFailed
 	} else if r.status == StatusDefunct {
 		log.Errorw("prediction rejected: server is defunct")
-		return nil, fmt.Errorf("server is defunct")
+		return nil, ErrDefunct
 	}
 	if req.CreatedAt == "" {
 		req.CreatedAt = util.NowIso()
 	}
 	r.mu.Lock()
 	if _, ok := r.pending[req.Id]; ok {
 		r.mu.Unlock()
-		log.Errorw("prediction rejected: prediction ID exists", "id", req.Id)
-		return nil, fmt.Errorf("prediction ID exists")
+		log.Errorw("prediction rejected: prediction exists", "id", req.Id)
+		return nil, ErrExists
 	}
 	r.mu.Unlock()
 

internal/server/server.go

@@ -81,9 +81,20 @@ func (h *Handler) Predict(w http.ResponseWriter, r *http.Request) {
 	}
 
 	c, err := h.runner.predict(req)
-	if err != nil {
+	if errors.Is(err, ErrDefunct) {
+		http.Error(w, err.Error(), http.StatusServiceUnavailable)
+		return
+	} else if errors.Is(err, ErrExists) {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	} else if errors.Is(err, ErrSetupFailed) {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	} else if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
 	}
+
 	if c == nil {
 		w.WriteHeader(http.StatusAccepted)
 		resp := PredictionResponse{Id: req.Id, Status: "starting"}