feat: support connect_timeout property

Add support for a connect_timeout property that sets the maximum time that the driver
will wait when creating a new connection to Spanner. This property only affects the
very first creation of a connection to Spanner for a given connector. Once a connection
has been established, all further connection creations will not use this value.

Fixes #576

Author: olavloite

connection_properties.go

@@ -461,6 +461,15 @@ var propertyDisableStatementCache = createConnectionProperty(
 	connectionstate.ContextStartup,
 	connectionstate.ConvertBool,
 )
+var propertyConnectTimeout = createConnectionProperty(
+	"connect_timeout",
+	"The amount of time to wait before timing out when creating a new connection.",
+	0,
+	false,
+	nil,
+	connectionstate.ContextStartup,
+	connectionstate.ConvertDuration,
+)
 
 // Generated read-only properties. These cannot be set by the user anywhere.
 var propertyCommitTimestamp = createReadOnlyConnectionProperty(

connectionstate/converters.go

@@ -113,7 +113,7 @@ func parseTimestamp(re *regexp.Regexp, params string) (time.Time, error) {
 func parseDuration(re *regexp.Regexp, value string) (time.Duration, error) {
 	matches := matchesToMap(re, value)
 	if matches["duration"] == "" && matches["number"] == "" && matches["null"] == "" {
-		return 0, spanner.ToSpannerError(status.Error(codes.InvalidArgument, fmt.Sprintf("No duration found: %v", value)))
+		return 0, spanner.ToSpannerError(status.Error(codes.InvalidArgument, fmt.Sprintf("No or invalid duration found: %v", value)))
 	}
 	if matches["duration"] != "" {
 		d, err := time.ParseDuration(matches["duration"])

driver.go

@@ -732,6 +732,17 @@ func openDriverConn(ctx context.Context, c *connector) (driver.Conn, error) {
 		c.connectorConfig.Project,
 		c.connectorConfig.Instance,
 		c.connectorConfig.Database)
+	if value, ok := c.initialPropertyValues[propertyConnectTimeout.Key()]; ok {
+		if timeout, err := value.GetValue(); err == nil {
+			if duration, ok := timeout.(time.Duration); ok {
+				var cancel context.CancelFunc
+				// This will set the actual timeout of the context to the lower of the
+				// current context timeout (if any) and the value from the connection property.
+				ctx, cancel = context.WithTimeout(ctx, duration)
+				defer cancel()
+			}
+		}
+	}
 
 	if err := c.increaseConnCount(ctx, databaseName, opts); err != nil {
 		return nil, err

driver_with_mockserver_test.go

@@ -5555,6 +5555,47 @@ func TestReturnResultSetMetadataAndStats(t *testing.T) {
 	}
 }
 
+func TestConnectTimeout(t *testing.T) {
+	t.Parallel()
+
+	server, _, serverTeardown := setupMockedTestServerWithDialect(t, databasepb.DatabaseDialect_GOOGLE_STANDARD_SQL)
+	defer serverTeardown()
+	db, err := sql.Open(
+		"spanner",
+		fmt.Sprintf("%s/projects/p/instances/i/databases/d?useplaintext=true;connect_timeout=1ms", server.Address))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer silentClose(db)
+
+	// Make the ExecuteStreamingSql method a bit slow, so the query that is used to detect the dialect responds a bit slowly.
+	server.TestSpanner.PutExecutionTime(testutil.MethodExecuteStreamingSql, testutil.SimulatedExecutionTime{MinimumExecutionTime: time.Millisecond * 10})
+
+	// Try to get/create a connection using a context without a deadline.
+	// This will cause the connect_timeout to be used.
+	c, err := db.Conn(context.Background())
+	if g, w := spanner.ErrCode(err), codes.DeadlineExceeded; g != w {
+		t.Fatalf("error code mismatch\n Got: %v\nWant: %v", g, w)
+	} else if c != nil {
+		_ = c.Close()
+	}
+}
+
+func TestInvalidConnectTimeout(t *testing.T) {
+	t.Parallel()
+
+	server, _, serverTeardown := setupMockedTestServerWithDialect(t, databasepb.DatabaseDialect_GOOGLE_STANDARD_SQL)
+	defer serverTeardown()
+	db, err := sql.Open(
+		"spanner",
+		fmt.Sprintf("%s/projects/p/instances/i/databases/d?useplaintext=true;connect_timeout='very long'", server.Address))
+	if g, w := spanner.ErrCode(err), codes.InvalidArgument; g != w {
+		t.Fatalf("error code mismatch\n Got: %v\nWant: %v", g, w)
+	} else if db != nil {
+		defer silentClose(db)
+	}
+}
+
 func numeric(v string) big.Rat {
 	res, _ := big.NewRat(1, 1).SetString(v)
 	return *res