database/sql: close driver.Connector if it implements 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

Fixes #41790

Change-Id: Idbd19763134438ed38288b9d44f16608e4e97fd7
GitHub-Last-Rev: 962c785dfb3bb6ad98b2216bcedd84ba383fe872
GitHub-Pull-Request: golang/go#41710
Reviewed-on: https://go-review.googlesource.com/c/go/+/258360
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
TryBot-Result: Go Bot <gobot@golang.org>

4 files changed, 28 insertions, 1 deletions

diff --git a/src/database/sql/driver/driver.go b/src/database/sql/driver/driver.go
index 5bbcf20db2..f09396175a 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.
+//
+// If a Connector implements io.Closer, the sql package's DB.Close
+// method will call Close and return error (if any).
 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 7605a2a6d2..1bfd1118aa 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 726aadb899..37bcb0d091 100644
--- a/src/database/sql/sql.go
+++ b/src/database/sql/sql.go
@@ -850,6 +850,12 @@ func (db *DB) Close() error {
 		}
 	}
 	db.stop()
+	if c, ok := db.connector.(io.Closer); ok {
+		err1 := c.Close()
+		if err1 != nil {
+			err = err1
+		}
+	}
 	return err
 }
 
diff --git a/src/database/sql/sql_test.go b/src/database/sql/sql_test.go
index 99bfd62491..c06e565ea9 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 {