fix: cache tenant routing on message hot path

server/db/mysql/adapter_tenant_route_cache_test.go

@@ -0,0 +1,66 @@
+//go:build mysql
+
+package mysql
+
+import (
+	"testing"
+	"time"
+
+	"github.com/tinode/chat/server/store/types"
+)
+
+func TestTenantRouteCacheExpiresAndInvalidates(t *testing.T) {
+	now := time.Now()
+	tenantID := types.TenantID(8)
+	tenantAdp := &adapter{tenantID: tenantID}
+	root := &adapter{
+		tenantDBRouting:   true,
+		tenantAdapters:    map[types.TenantID]*adapter{tenantID: tenantAdp},
+		tenantRouteExpiry: make(map[types.TenantID]time.Time),
+	}
+
+	root.cacheTenantAdapter(tenantID, tenantAdp, root.tenantRouteGeneration(), now.Add(time.Minute))
+	if got, ok := root.cachedTenantAdapter(tenantID, now); !ok || got != tenantAdp {
+		t.Fatalf("cached route = %p, %v; want %p, true", got, ok, tenantAdp)
+	}
+	if got, _, err := root.TenantAdapterFor(tenantID); err != nil || got != tenantAdp {
+		t.Fatalf("TenantAdapterFor cached route = %p, %v; want %p, nil", got, err, tenantAdp)
+	}
+
+	staleGeneration := root.tenantRouteGeneration()
+	root.InvalidateTenantRoute(tenantID)
+	if _, ok := root.cachedTenantAdapter(tenantID, now); ok {
+		t.Fatal("invalidated tenant route remained cached")
+	}
+	root.cacheTenantAdapter(tenantID, tenantAdp, staleGeneration, now.Add(time.Minute))
+	if _, ok := root.cachedTenantAdapter(tenantID, now); ok {
+		t.Fatal("an in-flight stale refresh repopulated the route cache")
+	}
+
+	root.cacheTenantAdapter(tenantID, tenantAdp, root.tenantRouteGeneration(), now.Add(-time.Second))
+	if _, ok := root.cachedTenantAdapter(tenantID, now); ok {
+		t.Fatal("expired tenant route remained cached")
+	}
+}
+
+func TestInvalidateAllTenantRoutes(t *testing.T) {
+	now := time.Now()
+	root := &adapter{
+		tenantDBRouting: true,
+		tenantAdapters: map[types.TenantID]*adapter{
+			8: {tenantID: 8},
+			9: {tenantID: 9},
+		},
+		tenantRouteExpiry: map[types.TenantID]time.Time{
+			8: now.Add(time.Minute),
+			9: now.Add(time.Minute),
+		},
+	}
+
+	root.InvalidateTenantRoute(0)
+	for _, tenantID := range []types.TenantID{8, 9} {
+		if _, ok := root.cachedTenantAdapter(tenantID, now); ok {
+			t.Fatalf("tenant %d route remained cached after global invalidation", tenantID)
+		}
+	}
+}