security: validate watchlist inputs

internal/features/watchlist/handler.go

@@ -2,7 +2,7 @@ package watchlist
 
 import (
 	"encoding/json"
-	"fmt"
+	"errors"
 	"log"
 	"net/http"
 	"strconv"
@@ -50,7 +50,7 @@ func (h *Handler) HandleUpdateWatchlist(w http.ResponseWriter, r *http.Request)
 	log.Printf("watchlist add: user_id=%s, anime_id=%s, title=%s", user.ID, animeIDStr, animeTitle)
 
 	animeID, err := strconv.ParseInt(animeIDStr, 10, 64)
-	if err != nil {
+	if err != nil || animeID <= 0 {
 		http.Error(w, "invalid anime ID", http.StatusBadRequest)
 		return
 	}
@@ -66,7 +66,12 @@ func (h *Handler) HandleUpdateWatchlist(w http.ResponseWriter, r *http.Request)
 	}
 
 	if err := h.svc.AddEntry(r.Context(), user.ID, req); err != nil {
-		http.Error(w, fmt.Sprintf("failed to update watchlist: %v", err), http.StatusInternalServerError)
+		if errors.Is(err, ErrInvalidAnimeID) || errors.Is(err, ErrInvalidStatus) {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+		log.Printf("watchlist add failed: user_id=%s anime_id=%d err=%v", user.ID, animeID, err)
+		http.Error(w, "failed to update watchlist", http.StatusInternalServerError)
 		return
 	}
 
@@ -88,14 +93,19 @@ func (h *Handler) HandleDeleteWatchlist(w http.ResponseWriter, r *http.Request)
 
 	path := r.URL.Path[len("/api/watchlist/"):]
 	animeID, err := strconv.ParseInt(path, 10, 64)
-	if err != nil {
+	if err != nil || animeID <= 0 {
 		http.Error(w, "invalid anime ID", http.StatusBadRequest)
 		return
 	}
 
 	anime, err := h.svc.RemoveEntry(r.Context(), user.ID, animeID)
 	if err != nil {
-		http.Error(w, fmt.Sprintf("failed to delete from watchlist: %v", err), http.StatusInternalServerError)
+		if errors.Is(err, ErrInvalidAnimeID) {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+		log.Printf("watchlist delete failed: user_id=%s anime_id=%d err=%v", user.ID, animeID, err)
+		http.Error(w, "failed to delete from watchlist", http.StatusInternalServerError)
 		return
 	}
 
@@ -150,7 +160,8 @@ func (h *Handler) HandleGetWatchlist(w http.ResponseWriter, r *http.Request) {
 
 	entries, err := h.svc.GetUserWatchlist(r.Context(), user.ID)
 	if err != nil {
-		http.Error(w, fmt.Sprintf("failed to fetch watchlist: %v", err), http.StatusInternalServerError)
+		log.Printf("watchlist fetch failed: user_id=%s err=%v", user.ID, err)
+		http.Error(w, "failed to fetch watchlist", http.StatusInternalServerError)
 		return
 	}
 
@@ -193,7 +204,8 @@ func (h *Handler) HandleExportWatchlist(w http.ResponseWriter, r *http.Request)
 
 	export, err := h.svc.Export(r.Context(), user.ID)
 	if err != nil {
-		http.Error(w, fmt.Sprintf("failed to export: %v", err), http.StatusInternalServerError)
+		log.Printf("watchlist export failed: user_id=%s err=%v", user.ID, err)
+		http.Error(w, "failed to export", http.StatusInternalServerError)
 		return
 	}
 

internal/features/watchlist/service.go

@@ -3,6 +3,7 @@ package watchlist
 import (
 	"context"
 	"database/sql"
+	"errors"
 	"fmt"
 	"time"
 
@@ -15,6 +16,19 @@ type Service struct {
 	db database.Querier
 }
 
+var (
+	ErrInvalidAnimeID = errors.New("invalid anime ID")
+	ErrInvalidStatus  = errors.New("invalid watchlist status")
+)
+
+var validStatuses = map[string]struct{}{
+	"watching":      {},
+	"completed":     {},
+	"on_hold":       {},
+	"dropped":       {},
+	"plan_to_watch": {},
+}
+
 func NewService(db database.Querier) *Service {
 	return &Service{db: db}
 }
@@ -30,8 +44,12 @@ type AddRequest struct {
 }
 
 func (s *Service) AddEntry(ctx context.Context, userID string, req AddRequest) error {
-	if req.AnimeID == 0 {
-		return fmt.Errorf("invalid anime ID")
+	if req.AnimeID <= 0 {
+		return ErrInvalidAnimeID
+	}
+
+	if _, ok := validStatuses[req.Status]; !ok {
+		return ErrInvalidStatus
 	}
 
 	_, err := s.db.UpsertAnime(ctx, database.UpsertAnimeParams{
@@ -62,8 +80,8 @@ func (s *Service) AddEntry(ctx context.Context, userID string, req AddRequest) e
 }
 
 func (s *Service) RemoveEntry(ctx context.Context, userID string, animeID int64) (database.Anime, error) {
-	if animeID == 0 {
-		return database.Anime{}, fmt.Errorf("invalid anime ID")
+	if animeID <= 0 {
+		return database.Anime{}, ErrInvalidAnimeID
 	}
 
 	anime, err := s.db.GetAnime(ctx, animeID)