fix: 503 при сбое GetScan вместо ложного 404 scan not found

- Store.GetScan возвращает (job, ok, error); Postgres отдаёт err при ошибке БД/JSON

- API: getScanOrWriteError → 503 scan storage temporarily unavailable

- Web UI: понятное сообщение для HTTP 503 при опросе скана

Made-with: Cursor

internal/api/handler.go

@@ -14,6 +14,9 @@ import (
 	"nettopo-go/internal/webui"
 )
 
+// errScanStorageUnavailable — ответ API при сбое GetScan (БД, а не «нет такого scan_id»).
+const errScanStorageUnavailable = "scan storage temporarily unavailable"
+
 type Handler struct {
 	store         scans.Store
 	run           *scans.Runner
@@ -83,6 +86,26 @@ func scanPathID(r *http.Request) string {
 	return strings.TrimSpace(raw)
 }
 
+// getScanOrWriteError загружает скан; при ошибке хранилища пишет 503, при отсутствии строки — 404 с notFoundMsg (или «scan not found»).
+func (h *Handler) getScanOrWriteError(w http.ResponseWriter, id, notFoundMsg string) (scans.ScanJob, bool) {
+	job, found, err := h.store.GetScan(id)
+	if err != nil {
+		log.Printf("GetScan id=%q (len=%d): %v", id, len(id), err)
+		writeError(w, http.StatusServiceUnavailable, errScanStorageUnavailable)
+		return scans.ScanJob{}, false
+	}
+	if !found {
+		msg := notFoundMsg
+		if msg == "" {
+			msg = "scan not found"
+		}
+		log.Printf("getScan: not found id=%q (len=%d) msg=%q", id, len(id), msg)
+		writeError(w, http.StatusNotFound, msg)
+		return scans.ScanJob{}, false
+	}
+	return job, true
+}
+
 func (h *Handler) Routes() http.Handler {
 	mux := http.NewServeMux()
 	webFS := http.FileServer(http.FS(webui.FS))
@@ -189,12 +212,10 @@ func (h *Handler) getScansDiff(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "both from and to are required")
 		return
 	}
-	if _, ok := h.store.GetScan(fromID); !ok {
-		writeError(w, http.StatusNotFound, "from scan not found")
+	if _, ok := h.getScanOrWriteError(w, fromID, "from scan not found"); !ok {
 		return
 	}
-	if _, ok := h.store.GetScan(toID); !ok {
-		writeError(w, http.StatusNotFound, "to scan not found")
+	if _, ok := h.getScanOrWriteError(w, toID, "to scan not found"); !ok {
 		return
 	}
 
@@ -221,10 +242,8 @@ func (h *Handler) getScan(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	job, ok := h.store.GetScan(id)
+	job, ok := h.getScanOrWriteError(w, id, "")
 	if !ok {
-		log.Printf("getScan: not found id=%q (len=%d)", id, len(id))
-		writeError(w, http.StatusNotFound, "scan not found")
 		return
 	}
 
@@ -241,9 +260,8 @@ func (h *Handler) postCancelScan(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "scan id is required")
 		return
 	}
-	if _, ok := h.store.GetScan(id); !ok {
-		log.Printf("postCancelScan: not found id=%q (len=%d)", id, len(id))
-		writeError(w, http.StatusNotFound, "scan not found")
+	cur, ok := h.getScanOrWriteError(w, id, "")
+	if !ok {
 		return
 	}
 	runnerSignaled := false
@@ -254,7 +272,6 @@ func (h *Handler) postCancelScan(w http.ResponseWriter, r *http.Request) {
 		writeJSON(w, http.StatusOK, map[string]any{"ok": true, "runner_canceled": true})
 		return
 	}
-	cur, _ := h.store.GetScan(id)
 	if cur.Status == "queued" {
 		fin := time.Now().UTC()
 		_, _ = h.store.UpdateScan(id, scans.ScanUpdate{Status: "canceled", FinishedAt: &fin})
@@ -270,8 +287,7 @@ func (h *Handler) getScanHosts(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "scan id is required")
 		return
 	}
-	if _, ok := h.store.GetScan(id); !ok {
-		writeError(w, http.StatusNotFound, "scan not found")
+	if _, ok := h.getScanOrWriteError(w, id, ""); !ok {
 		return
 	}
 
@@ -296,8 +312,7 @@ func (h *Handler) getScanPorts(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "scan id is required")
 		return
 	}
-	if _, ok := h.store.GetScan(id); !ok {
-		writeError(w, http.StatusNotFound, "scan not found")
+	if _, ok := h.getScanOrWriteError(w, id, ""); !ok {
 		return
 	}
 
@@ -322,8 +337,7 @@ func (h *Handler) getScanSNMP(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "scan id is required")
 		return
 	}
-	if _, ok := h.store.GetScan(id); !ok {
-		writeError(w, http.StatusNotFound, "scan not found")
+	if _, ok := h.getScanOrWriteError(w, id, ""); !ok {
 		return
 	}
 
@@ -348,8 +362,7 @@ func (h *Handler) getScanLLDP(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "scan id is required")
 		return
 	}
-	if _, ok := h.store.GetScan(id); !ok {
-		writeError(w, http.StatusNotFound, "scan not found")
+	if _, ok := h.getScanOrWriteError(w, id, ""); !ok {
 		return
 	}
 
@@ -374,8 +387,7 @@ func (h *Handler) getScanInterfaces(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "scan id is required")
 		return
 	}
-	if _, ok := h.store.GetScan(id); !ok {
-		writeError(w, http.StatusNotFound, "scan not found")
+	if _, ok := h.getScanOrWriteError(w, id, ""); !ok {
 		return
 	}
 	ip := strings.TrimSpace(r.URL.Query().Get("ip"))
@@ -403,8 +415,7 @@ func (h *Handler) getScanPortDevices(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "scan id is required")
 		return
 	}
-	if _, ok := h.store.GetScan(id); !ok {
-		writeError(w, http.StatusNotFound, "scan not found")
+	if _, ok := h.getScanOrWriteError(w, id, ""); !ok {
 		return
 	}
 	ip := strings.TrimSpace(r.URL.Query().Get("ip"))
@@ -463,8 +474,7 @@ func (h *Handler) getScanMacLocations(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "scan id is required")
 		return
 	}
-	if _, ok := h.store.GetScan(id); !ok {
-		writeError(w, http.StatusNotFound, "scan not found")
+	if _, ok := h.getScanOrWriteError(w, id, ""); !ok {
 		return
 	}
 	raw := strings.TrimSpace(r.URL.Query().Get("mac"))
@@ -612,8 +622,7 @@ func (h *Handler) getScanLinks(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "scan id is required")
 		return
 	}
-	if _, ok := h.store.GetScan(id); !ok {
-		writeError(w, http.StatusNotFound, "scan not found")
+	if _, ok := h.getScanOrWriteError(w, id, ""); !ok {
 		return
 	}
 
@@ -675,8 +684,7 @@ func (h *Handler) getScanTopology(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusBadRequest, "scan id is required")
 		return
 	}
-	if _, ok := h.store.GetScan(id); !ok {
-		writeError(w, http.StatusNotFound, "scan not found")
+	if _, ok := h.getScanOrWriteError(w, id, ""); !ok {
 		return
 	}