Merge Updater structs (#1069)

* Move Updater structs to shared and use it for postgres

* Add constructors for NewXXXUpdater and a useTxns flag

In sqlite, we set useTxns=false and comment why.

* Handle nil txn

* Handle nil in transaction

* Missed one

* Close the txn at the right time

* Don't close the transaction as we reuse it between calls

roomserver/storage/shared/prepare.go

@@ -16,6 +16,7 @@
 package shared
 
 import (
+	"context"
 	"database/sql"
 )
 
@@ -34,3 +35,26 @@ func (s StatementList) Prepare(db *sql.DB) (err error) {
 	}
 	return
 }
+
+type transaction struct {
+	ctx context.Context
+	txn *sql.Tx
+}
+
+// Commit implements types.Transaction
+func (t *transaction) Commit() error {
+	if t.txn == nil {
+		// The Updater structs can operate in useTxns=false mode. The code will still call this though.
+		return nil
+	}
+	return t.txn.Commit()
+}
+
+// Rollback implements types.Transaction
+func (t *transaction) Rollback() error {
+	if t.txn == nil {
+		// The Updater structs can operate in useTxns=false mode. The code will still call this though.
+		return nil
+	}
+	return t.txn.Rollback()
+}