fix: a huge export or list page answers an empty page instead of panicking (WR-14)

(page-1)*perPage overflowed for a large page and sliced out of range.
Export compares the page with the page count before multiplying, and the
list endpoints cap the page number.

classes/transfer.go

@@ -160,9 +160,11 @@ func (s *Service) Export(ctx context.Context, dataset, delimiter string, page, p
 			page = 1
 		}
 		out.Page = page
-		start := (page - 1) * perPage
-		if start > len(rows) {
-			start = len(rows)
+		// A page past the last is empty; compared before multiplying, so a
+		// huge page cannot overflow into a negative start (WR-14).
+		start := len(rows)
+		if page <= out.Pages {
+			start = (page - 1) * perPage
 		}
 		end := min(start+perPage, len(rows))
 		rows = rows[start:end]

controllers/api/auth.go

@@ -184,10 +184,12 @@ func read(ctx context.Context, svc *classes.Service) (*gorm.DB, error) {
 	return svc.DB(ctx)
 }
 
-// The page sizes of the list endpoints.
+// The page sizes of the list endpoints, and the highest page number read
+// (a later page is empty anyway).
 const (
 	defaultPerPage = 50
 	maxPerPage     = 200
+	maxPage        = 1_000_000
 )
 
 // ListInput is the paging and search query every list tool shares.
@@ -206,6 +208,10 @@ func listParams(r *http.Request) ListInput {
 	if in.Page < 1 {
 		in.Page = 1
 	}
+	// (Page-1)*PerPage must not overflow into a negative offset (WR-14).
+	if in.Page > maxPage {
+		in.Page = maxPage
+	}
 	if in.PerPage < 1 {
 		in.PerPage = defaultPerPage
 	}

transfer_test.go

@@ -73,6 +73,16 @@ func TestCSVTransfer(t *testing.T) {
 		t.Fatalf("filename = %v", exp["filename"])
 	}
 
+	// A huge page number is an empty page, not a panic (WR-14); so is a
+	// list page.
+	far := env.mcpExpect(t, http.StatusOK, http.MethodGet, "/_seo/api/v1/export?dataset=redirects&page=9223372036854777", agent, nil)
+	if c, _ := far["csv"].(string); strings.Contains(c, "/e1") {
+		t.Fatalf("export of a huge page = %v, want no rows", far)
+	}
+	if l := env.mcpExpect(t, http.StatusOK, http.MethodGet, "/_seo/api/v1/redirects?page=9223372036854775807&per_page=200", agent, nil); len(l["data"].([]any)) != 0 {
+		t.Fatalf("list of a huge page = %v, want no rows", l)
+	}
+
 	preview := env.mcpExpect(t, http.StatusOK, http.MethodPost, "/_seo/api/v1/import", agent, map[string]any{"dataset": "redirects", "csv": csv, "delimiter": ";", "dry_run": true})
 	if s := summary(t, preview); s["unchanged"] != 2 || s["new"] != 0 || s["changed"] != 0 || s["refused"] != 0 {
 		t.Fatalf("re-import of the export = %v, want 2 unchanged", preview)