fix: upload part tmp+rename (B4), transactional last-admin DeleteUser (B5), RowsAffected order (B13)

backend/cmd/webui/handlers/uploads.go

@@ -198,8 +198,11 @@ func (h *H) UploadPart(c *gin.Context) {
 	}
 	lo, hi := chunkRange(m, idx)
 	c.Request.Body = http.MaxBytesReader(c.Writer, c.Request.Body, hi-lo)
+	// B4: write to .tmp then rename — prevents truncated parts from being
+	// reported as "received" by UploadStatus if the process crashes mid-write.
 	p := filepath.Join(dir, "parts", strconv.FormatInt(idx, 10))
-	f, e := os.OpenFile(p, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o644)
+	tmp := p + ".tmp"
+	f, e := os.OpenFile(tmp, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o644)
 	if e != nil {
 		err(c, http.StatusInternalServerError, "internal", "create part")
 		return
@@ -207,7 +210,7 @@ func (h *H) UploadPart(c *gin.Context) {
 	n, e := io.Copy(f, c.Request.Body)
 	f.Close()
 	if e != nil || n != hi-lo {
-		os.Remove(p)
+		os.Remove(tmp)
 		var mbe *http.MaxBytesError
 		code, msg := "too_large", "part size mismatch"
 		if errors.As(e, &mbe) {
@@ -216,6 +219,11 @@ func (h *H) UploadPart(c *gin.Context) {
 		err(c, http.StatusRequestEntityTooLarge, code, msg)
 		return
 	}
+	if e := os.Rename(tmp, p); e != nil {
+		os.Remove(tmp)
+		err(c, http.StatusInternalServerError, "internal", "rename part")
+		return
+	}
 	c.JSON(http.StatusAccepted, gin.H{"accepted": true})
 }
 

backend/cmd/webui/handlers/users.go

@@ -8,15 +8,13 @@ import (
 
 	"github.com/gin-gonic/gin"
 	"github.com/jackc/pgx/v5"
-	"github.com/jackc/pgx/v5/pgconn"
 
 	"booklib/internal/auth"
+	"booklib/internal/store"
 )
 
-func isUnique(e error) bool {
+// isUnique is a convenience alias for store.IsUniqueViolation.
-	var pgErr *pgconn.PgError
+func isUnique(e error) bool { return store.IsUniqueViolation(e) }
-	return errors.As(e, &pgErr) && pgErr.Code == "23505"
-}
 
 func (h *H) ListUsers(c *gin.Context) {
 	users, e := h.st.ListUsers(c)
@@ -73,23 +71,16 @@ func (h *H) DeleteUser(c *gin.Context) {
 		err(c, http.StatusBadRequest, "bad_request", "cannot delete yourself")
 		return
 	}
-	target, e := h.st.GetUserByID(c, id)
+	// B5: transactional last-admin check eliminates TOCTOU race.
-	if e != nil {
+	if e := h.st.DeleteUser(c, id); e != nil {
 		if errors.Is(e, pgx.ErrNoRows) {
 			err(c, http.StatusNotFound, "not_found", "no such user")
 			return
 		}
-		dbErr(c, e)
+		if errors.Is(e, store.ErrLastAdmin) {
-		return
-	}
-	if target.Role == "admin" {
-		n, _ := h.st.CountAdmins(c) // 防删光最后一个 admin
-		if n <= 1 {
 			err(c, http.StatusBadRequest, "bad_request", "cannot delete the last admin")
 			return
 		}
-	}
-	if e := h.st.DeleteUser(c, id); e != nil {
 		dbErr(c, e)
 		return
 	}

backend/internal/store/store.go

@@ -2,12 +2,23 @@ package store
 
 import (
 	"context"
+	"errors"
 	"time"
 
 	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgconn"
 	"github.com/jackc/pgx/v5/pgxpool"
 )
 
+// ErrLastAdmin is returned by DeleteUser when attempting to delete the last admin.
+var ErrLastAdmin = errors.New("cannot delete the last admin")
+
+// IsUniqueViolation reports whether err is a PostgreSQL unique constraint violation (23505).
+func IsUniqueViolation(err error) bool {
+	var pgErr *pgconn.PgError
+	return errors.As(err, &pgErr) && pgErr.Code == "23505"
+}
+
 type Store struct{ P *pgxpool.Pool }
 
 func New(p *pgxpool.Pool) *Store { return &Store{P: p} }
@@ -103,9 +114,31 @@ func (s *Store) ListUsers(ctx context.Context) ([]User, error) {
 	return out, rows.Err()
 }
 
+// DeleteUser deletes a user with a transactional last-admin check (B5).
+// Returns ErrLastAdmin if the target is the last admin.
 func (s *Store) DeleteUser(ctx context.Context, id int64) error {
-	_, err := s.P.Exec(ctx, "DELETE FROM users WHERE id=$1", id)
+	tx, err := s.P.Begin(ctx)
+	if err != nil {
 		return err
+	}
+	defer tx.Rollback(ctx)
+	var role string
+	if err := tx.QueryRow(ctx, "SELECT role FROM users WHERE id=$1 FOR UPDATE", id).Scan(&role); err != nil {
+		return err // includes pgx.ErrNoRows
+	}
+	if role == "admin" {
+		var n int
+		if err := tx.QueryRow(ctx, "SELECT count(*) FROM users WHERE role='admin'").Scan(&n); err != nil {
+			return err
+		}
+		if n <= 1 {
+			return ErrLastAdmin
+		}
+	}
+	if _, err := tx.Exec(ctx, "DELETE FROM users WHERE id=$1", id); err != nil {
+		return err
+	}
+	return tx.Commit(ctx)
 }
 
 func scanUser(row pgx.Row) (User, error) {
@@ -114,12 +147,7 @@ func scanUser(row pgx.Row) (User, error) {
 	return u, err
 }
 
-// CountAdmins 供 Task 5 的"最后一个 admin 不可删"保护
+
-func (s *Store) CountAdmins(ctx context.Context) (int, error) {
-	var n int
-	err := s.P.QueryRow(ctx, "SELECT count(*) FROM users WHERE role='admin'").Scan(&n)
-	return n, err
-}
 
 // ---------- libraries ----------
 
@@ -357,12 +385,18 @@ func (s *Store) ListBookmarks(ctx context.Context, userID, libID int64, bookPath
 
 func (s *Store) UpdateBookmarkNote(ctx context.Context, userID, id int64, note string) (bool, error) {
 	res, err := s.P.Exec(ctx, `UPDATE bookmarks SET note=$3 WHERE id=$1 AND user_id=$2`, id, userID, note)
-	return res.RowsAffected() > 0, err
+	if err != nil {
+		return false, err
+	}
+	return res.RowsAffected() > 0, nil
 }
 
 func (s *Store) DeleteBookmark(ctx context.Context, userID, id int64) (bool, error) {
 	res, err := s.P.Exec(ctx, `DELETE FROM bookmarks WHERE id=$1 AND user_id=$2`, id, userID)
-	return res.RowsAffected() > 0, err
+	if err != nil {
+		return false, err
+	}
+	return res.RowsAffected() > 0, nil
 }
 
 func (s *Store) GetProgress(ctx context.Context, userID, libID int64, bookPath string) (Progress, error) {

backend/internal/store/store_test.go

@@ -2,6 +2,7 @@ package store
 
 import (
 	"context"
+	"errors"
 	"os"
 	"testing"
 
@@ -129,3 +130,50 @@ func TestProgressUpsertAndJoin(t *testing.T) {
 		t.Fatalf("views %+v", views)
 	}
 }
+
+func TestDeleteUserLastAdmin(t *testing.T) {
+	s := setup(t)
+	ctx := context.Background()
+	id, err := s.CreateUser(ctx, "onlyadmin", "hash", "admin")
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = s.DeleteUser(ctx, id)
+	if !errors.Is(err, ErrLastAdmin) {
+		t.Fatalf("expected ErrLastAdmin, got %v", err)
+	}
+	// Verify user still exists.
+	_, err = s.GetUserByID(ctx, id)
+	if err != nil {
+		t.Fatal("admin should still exist after blocked delete")
+	}
+}
+
+func TestDeleteUserNonLastAdmin(t *testing.T) {
+	s := setup(t)
+	ctx := context.Background()
+	id1, _ := s.CreateUser(ctx, "admin1", "h", "admin")
+	_, _ = s.CreateUser(ctx, "admin2", "h", "admin")
+	if err := s.DeleteUser(ctx, id1); err != nil {
+		t.Fatalf("should allow deleting non-last admin: %v", err)
+	}
+}
+
+func TestDeleteUserMember(t *testing.T) {
+	s := setup(t)
+	ctx := context.Background()
+	id, _ := s.CreateUser(ctx, "member", "h", "member")
+	if err := s.DeleteUser(ctx, id); err != nil {
+		t.Fatalf("member delete should succeed: %v", err)
+	}
+}
+
+func TestIsUniqueViolation(t *testing.T) {
+	s := setup(t)
+	ctx := context.Background()
+	_, _ = s.CreateUser(ctx, "dup", "h", "member")
+	_, err := s.CreateUser(ctx, "dup", "h", "member")
+	if !IsUniqueViolation(err) {
+		t.Fatalf("expected unique violation, got %v", err)
+	}
+}