From 0cf218e26ee152d10334074048e27a9f825dac97 Mon Sep 17 00:00:00 2001
From: Ivan Trubach <mr.trubach@icloud.com>
Date: Wed, 30 Sep 2020 12:31:01 +0300
Subject: [PATCH] database/sql: close driver.Connector if it implements an
 io.Closer

This change allows driver implementations to manage resources in
driver.Connector, e.g. to share the same underlying database handle
between multiple connections. That is, it allows embedded databases
with in-memory backends like SQLite and Genji to safely release the
resources once the sql.DB is closed.

This makes it possible to address oddities with in-memory stores in
SQLite and Genji drivers without introducing too much complexity in
the driver implementations.

See also:
- https://github.com/mattn/go-sqlite3/issues/204
- https://github.com/mattn/go-sqlite3/issues/511
- https://github.com/genjidb/genji/issues/210
---
 src/database/sql/driver/driver.go |  3 +++
 src/database/sql/fakedb_test.go   |  9 +++++++++
 src/database/sql/sql.go           |  3 +++
 src/database/sql/sql_test.go      | 11 ++++++++++-
 4 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/src/database/sql/driver/driver.go b/src/database/sql/driver/driver.go
index 5bbcf20db2f07d..d1702a624e066e 100644
--- a/src/database/sql/driver/driver.go
+++ b/src/database/sql/driver/driver.go
@@ -115,6 +115,9 @@ type DriverContext interface {
 // DriverContext's OpenConnector method, to allow drivers
 // access to context and to avoid repeated parsing of driver
 // configuration.
+//
+// A Connector may optionally implement io.Closer interface
+// to release the resources when sql.DB is closed.
 type Connector interface {
 	// Connect returns a connection to the database.
 	// Connect may return a cached connection (one previously
diff --git a/src/database/sql/fakedb_test.go b/src/database/sql/fakedb_test.go
index 7605a2a6d23e03..1bfd1118aad68b 100644
--- a/src/database/sql/fakedb_test.go
+++ b/src/database/sql/fakedb_test.go
@@ -56,6 +56,7 @@ type fakeConnector struct {
 	name string
 
 	waiter func(context.Context)
+	closed bool
 }
 
 func (c *fakeConnector) Connect(context.Context) (driver.Conn, error) {
@@ -68,6 +69,14 @@ func (c *fakeConnector) Driver() driver.Driver {
 	return fdriver
 }
 
+func (c *fakeConnector) Close() error {
+	if c.closed {
+		return errors.New("fakedb: connector is closed")
+	}
+	c.closed = true
+	return nil
+}
+
 type fakeDriverCtx struct {
 	fakeDriver
 }
diff --git a/src/database/sql/sql.go b/src/database/sql/sql.go
index 726aadb8990e68..a1286ca650508f 100644
--- a/src/database/sql/sql.go
+++ b/src/database/sql/sql.go
@@ -850,6 +850,9 @@ func (db *DB) Close() error {
 		}
 	}
 	db.stop()
+	if c, ok := db.connector.(io.Closer); ok {
+		err = c.Close()
+	}
 	return err
 }
 
diff --git a/src/database/sql/sql_test.go b/src/database/sql/sql_test.go
index 99bfd62491fa3b..c06e565ea9c7a5 100644
--- a/src/database/sql/sql_test.go
+++ b/src/database/sql/sql_test.go
@@ -4059,9 +4059,18 @@ func TestOpenConnector(t *testing.T) {
 	}
 	defer db.Close()
 
-	if _, is := db.connector.(*fakeConnector); !is {
+	c, ok := db.connector.(*fakeConnector)
+	if !ok {
 		t.Fatal("not using *fakeConnector")
 	}
+
+	if err := db.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	if !c.closed {
+		t.Fatal("connector is not closed")
+	}
 }
 
 type ctxOnlyDriver struct {