1 files changed, 172 insertions, 0 deletions
diff --git a/internal/sqlutil/sql.go b/internal/sqlutil/sql.go
new file mode 100644
index 00000000..a25a4a5b
--- /dev/null
+++ b/internal/sqlutil/sql.go
@@ -0,0 +1,172 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sqlutil
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"runtime"
+	"time"
+
+	"go.uber.org/atomic"
+)
+
+// ErrUserExists is returned if a username already exists in the database.
+var ErrUserExists = errors.New("Username already exists")
+
+// A Transaction is something that can be committed or rolledback.
+type Transaction interface {
+	// Commit the transaction
+	Commit() error
+	// Rollback the transaction.
+	Rollback() error
+}
+
+// EndTransaction ends a transaction.
+// If the transaction succeeded then it is committed, otherwise it is rolledback.
+// You MUST check the error returned from this function to be sure that the transaction
+// was applied correctly. For example, 'database is locked' errors in sqlite will happen here.
+func EndTransaction(txn Transaction, succeeded *bool) error {
+	if *succeeded {
+		return txn.Commit() // nolint: errcheck
+	} else {
+		return txn.Rollback() // nolint: errcheck
+	}
+}
+
+// WithTransaction runs a block of code passing in an SQL transaction
+// If the code returns an error or panics then the transactions is rolledback
+// Otherwise the transaction is committed.
+func WithTransaction(db *sql.DB, fn func(txn *sql.Tx) error) (err error) {
+	txn, err := db.Begin()
+	if err != nil {
+		return
+	}
+	succeeded := false
+	defer func() {
+		err2 := EndTransaction(txn, &succeeded)
+		if err == nil && err2 != nil { // failed to commit/rollback
+			err = err2
+		}
+	}()
+
+	err = fn(txn)
+	if err != nil {
+		return
+	}
+
+	succeeded = true
+	return
+}
+
+// TxStmt wraps an SQL stmt inside an optional transaction.
+// If the transaction is nil then it returns the original statement that will
+// run outside of a transaction.
+// Otherwise returns a copy of the statement that will run inside the transaction.
+func TxStmt(transaction *sql.Tx, statement *sql.Stmt) *sql.Stmt {
+	if transaction != nil {
+		statement = transaction.Stmt(statement)
+	}
+	return statement
+}
+
+// Hack of the century
+func QueryVariadic(count int) string {
+	return QueryVariadicOffset(count, 0)
+}
+
+func QueryVariadicOffset(count, offset int) string {
+	str := "("
+	for i := 0; i < count; i++ {
+		str += fmt.Sprintf("$%d", i+offset+1)
+		if i < (count - 1) {
+			str += ", "
+		}
+	}
+	str += ")"
+	return str
+}
+
+func SQLiteDriverName() string {
+	if runtime.GOOS == "js" {
+		return "sqlite3_js"
+	}
+	return "sqlite3"
+}
+
+// DbProperties functions return properties used by database/sql/DB
+type DbProperties interface {
+	MaxIdleConns() int
+	MaxOpenConns() int
+	ConnMaxLifetime() time.Duration
+}
+
+// TransactionWriter allows queuing database writes so that you don't
+// contend on database locks in, e.g. SQLite. Only one task will run
+// at a time on a given TransactionWriter.
+type TransactionWriter struct {
+	running atomic.Bool
+	todo    chan transactionWriterTask
+}
+
+func NewTransactionWriter() *TransactionWriter {
+	return &TransactionWriter{
+		todo: make(chan transactionWriterTask),
+	}
+}
+
+// transactionWriterTask represents a specific task.
+type transactionWriterTask struct {
+	db   *sql.DB
+	f    func(txn *sql.Tx) error
+	wait chan error
+}
+
+// Do queues a task to be run by a TransactionWriter. The function
+// provided will be ran within a transaction as supplied by the
+// database parameter. This will block until the task is finished.
+func (w *TransactionWriter) Do(db *sql.DB, f func(txn *sql.Tx) error) error {
+	if w.todo == nil {
+		return errors.New("not initialised")
+	}
+	if !w.running.Load() {
+		go w.run()
+	}
+	task := transactionWriterTask{
+		db:   db,
+		f:    f,
+		wait: make(chan error, 1),
+	}
+	w.todo <- task
+	return <-task.wait
+}
+
+// run processes the tasks for a given transaction writer. Only one
+// of these goroutines will run at a time. A transaction will be
+// opened using the database object from the task and then this will
+// be passed as a parameter to the task function.
+func (w *TransactionWriter) run() {
+	if !w.running.CAS(false, true) {
+		return
+	}
+	defer w.running.Store(false)
+	for task := range w.todo {
+		task.wait <- WithTransaction(task.db, func(txn *sql.Tx) error {
+			return task.f(txn)
+		})
+		close(task.wait)
+	}
+}