feat(12.2-01): add deferred bindings, guarded upload store and purge

- deferred_bindings migration set under summercms.deferred with backend_user_id
- lagoon.DeferredBind/Unbind/Bindings/Forget/Slaves scoped by DeferredKey
- lagoon.PurgeDeferred with SKIP LOCKED batches and after-commit blob deletes
- attach.Store with the ported image guard, extension and MIME limits
- attach.Relation, attach.HasRelations, attach.BlobKeys, File.ThumbKey
- lagoon README and attachments docs

modules/lagoon/deferred_migrations.go

@@ -0,0 +1,55 @@
+package lagoon
+
+import (
+	"github.com/go-gormigrate/gormigrate/v2"
+	"gorm.io/gorm"
+)
+
+// DeferredHistoryID is the history id of the deferred-binding migration set;
+// its gormigrate table is summer_migrations_summercms_deferred.
+const DeferredHistoryID = "summercms.deferred"
+
+// DeferredBindingMigrations creates WinterCMS's deferred_bindings table,
+// folded from winter/storm's 2013_10_01_000001_Db_Deferred_Bindings.php and
+// 2021_01_19_000001_Db_Add_Pivot_Data_To_Deferred_Bindings.php. One column is
+// added: backend_user_id, the backend admin who owns the binding, so a
+// session key replayed by another admin matches nothing. master_type and
+// slave_type hold morph type strings (see MorphType), never PHP class names
+// of framework internals. Rolling the set back drops the table.
+var DeferredBindingMigrations = []*gormigrate.Migration{
+	{
+		ID: "202610020001_create_deferred_bindings",
+		Migrate: func(tx *gorm.DB) error {
+			stmts := []string{
+				`CREATE TABLE deferred_bindings (
+	id SERIAL PRIMARY KEY,
+	master_type TEXT NOT NULL,
+	master_field TEXT NOT NULL,
+	slave_type TEXT NOT NULL,
+	slave_id TEXT NOT NULL,
+	pivot_data TEXT,
+	session_key TEXT NOT NULL,
+	is_bind BOOLEAN NOT NULL DEFAULT TRUE,
+	backend_user_id INTEGER NOT NULL,
+	created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+	updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+)`,
+				`CREATE INDEX deferred_bindings_master_type_index ON deferred_bindings (master_type)`,
+				`CREATE INDEX deferred_bindings_master_field_index ON deferred_bindings (master_field)`,
+				`CREATE INDEX deferred_bindings_slave_type_index ON deferred_bindings (slave_type)`,
+				`CREATE INDEX deferred_bindings_slave_id_index ON deferred_bindings (slave_id)`,
+				`CREATE INDEX deferred_bindings_session_lookup_index ON deferred_bindings (session_key, backend_user_id, master_type)`,
+				`CREATE INDEX deferred_bindings_created_at_index ON deferred_bindings (created_at)`,
+			}
+			for _, stmt := range stmts {
+				if err := tx.Exec(stmt).Error; err != nil {
+					return err
+				}
+			}
+			return nil
+		},
+		Rollback: func(tx *gorm.DB) error {
+			return tx.Exec("DROP TABLE IF EXISTS deferred_bindings").Error
+		},
+	},
+}