implement driver.Pinger interface

conn_go18.go

@@ -76,6 +76,18 @@ func (cn *conn) BeginTx(ctx context.Context, opts driver.TxOptions) (driver.Tx,
 	return tx, nil
 }
 
+func (cn *conn) Ping(ctx context.Context) error {
+	if finish := cn.watchCancel(ctx); finish != nil {
+		defer finish()
+	}
+	rows, err := cn.simpleQuery("SELECT 'lib/pq ping test';")
+	if err != nil {
+		return driver.ErrBadConn // https://golang.org/pkg/database/sql/driver/#Pinger
+	}
+	rows.Close()
+	return nil
+}
+
 func (cn *conn) watchCancel(ctx context.Context) func() {
 	if done := ctx.Done(); done != nil {
 		finished := make(chan struct{})

go19_test.go

@@ -0,0 +1,69 @@
+// +build go1.9
+
+package pq
+
+import (
+	"context"
+	"database/sql"
+	"database/sql/driver"
+	"reflect"
+	"testing"
+)
+
+func TestPing(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	db := openTestConn(t)
+	defer db.Close()
+
+	if _, ok := reflect.TypeOf(db).MethodByName("Conn"); !ok {
+		t.Skipf("Conn method undefined on type %T, skipping test (requires at least go1.9)", db)
+	}
+
+	if err := db.PingContext(ctx); err != nil {
+		t.Fatal("expected Ping to succeed")
+	}
+	defer cancel()
+
+	// grab a connection
+	conn, err := db.Conn(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// start a transaction and read backend pid of our connection
+	tx, err := conn.BeginTx(ctx, &sql.TxOptions{
+		Isolation: sql.LevelDefault,
+		ReadOnly:  true,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	rows, err := tx.Query("SELECT pg_backend_pid()")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer rows.Close()
+
+	// read the pid from result
+	var pid int
+	for rows.Next() {
+		if err := rows.Scan(&pid); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if rows.Err() != nil {
+		t.Fatal(err)
+	}
+	if err := tx.Rollback(); err != nil {
+		t.Fatal(err)
+	}
+
+	// kill the process which handles our connection and test if the ping fails
+	if _, err := db.Exec("SELECT pg_terminate_backend($1)", pid); err != nil {
+		t.Fatal(err)
+	}
+	if err := conn.PingContext(ctx); err != driver.ErrBadConn {
+		t.Fatalf("expected error %s, instead got %s", driver.ErrBadConn, err)
+	}
+}