vtgate: Use the time zone setting correctly

go/test/endtoend/vtgate/queries/misc/misc_test.go

@@ -17,13 +17,16 @@ limitations under the License.
 package misc
 
 import (
+	"context"
 	"database/sql"
 	"fmt"
 	"strconv"
 	"strings"
 	"testing"
 	"time"
 
+	"vitess.io/vitess/go/mysql"
+
 	_ "github.com/go-sql-driver/mysql"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -473,3 +476,49 @@ func TestEnumSetVals(t *testing.T) {
 	mcmp.AssertMatches("select id, enum_col, cast(enum_col as signed) from tbl_enum_set order by enum_col, id", `[[INT64(4) ENUM("xsmall") INT64(1)] [INT64(2) ENUM("small") INT64(2)] [INT64(1) ENUM("medium") INT64(3)] [INT64(5) ENUM("medium") INT64(3)] [INT64(3) ENUM("large") INT64(4)]]`)
 	mcmp.AssertMatches("select id, set_col, cast(set_col as unsigned) from tbl_enum_set order by set_col, id", `[[INT64(4) SET("a,b") UINT64(3)] [INT64(3) SET("c") UINT64(4)] [INT64(5) SET("a,d") UINT64(9)] [INT64(1) SET("a,b,e") UINT64(19)] [INT64(2) SET("e,f,g") UINT64(112)]]`)
 }
+
+func TestTimeZones(t *testing.T) {
+	testCases := []struct {
+		name         string
+		targetTZ     string
+		expectedDiff time.Duration
+	}{
+		{"UTC to +08:00", "+08:00", 8 * time.Hour},
+		{"UTC to -08:00", "-08:00", -8 * time.Hour},
+		{"UTC to +05:30", "+05:30", 5*time.Hour + 30*time.Minute},
+		{"UTC to -05:45", "-05:45", -(5*time.Hour + 45*time.Minute)},
+		{"UTC to +09:00", "+09:00", 9 * time.Hour},
+		{"UTC to -12:00", "-12:00", -12 * time.Hour},
+	}
+
+	// Connect to Vitess
+	conn, err := mysql.Connect(context.Background(), &vtParams)
+	require.NoError(t, err)
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			// Set the initial time zone and get the time
+			utils.Exec(t, conn, "set time_zone = '+00:00'")
+			rs1 := utils.Exec(t, conn, "select now()")
+
+			// Set the target time zone and get the time
+			utils.Exec(t, conn, fmt.Sprintf("set time_zone = '%s'", tc.targetTZ))
+			rs2 := utils.Exec(t, conn, "select now()")
+
+			// Parse the times from the query result
+			layout := "2006-01-02 15:04:05" // MySQL default datetime format
+			time1, err := time.Parse(layout, rs1.Rows[0][0].ToString())
+			require.NoError(t, err)
+			time2, err := time.Parse(layout, rs2.Rows[0][0].ToString())
+			require.NoError(t, err)
+
+			// Calculate the actual difference between time2 and time1
+			actualDiff := time2.Sub(time1)
+			allowableDeviation := time.Second // allow up to 1-second difference
+
+			// Use a range to allow for slight variations
+			require.InDeltaf(t, tc.expectedDiff.Seconds(), actualDiff.Seconds(), allowableDeviation.Seconds(),
+				"time2 should be approximately %v after time1, within 1 second tolerance\n%v vs %v", tc.expectedDiff, time1, time2)
+		})
+	}
+}

go/vt/vtgate/executor_set_test.go

@@ -625,3 +625,22 @@ func TestExecutorSetAndSelect(t *testing.T) {
 		})
 	}
 }
+
+// TestTimeZone verifies that setting different time zones in the session
+// results in different outputs for the `now()` function.
+func TestExecutorTimeZone(t *testing.T) {
+	e, _, _, _, ctx := createExecutorEnv(t)
+
+	session := NewAutocommitSession(&vtgatepb.Session{TargetString: KsTestUnsharded, EnableSystemSettings: true})
+	session.SetSystemVariable("time_zone", "'+08:00'")
+
+	qr, err := e.Execute(ctx, nil, "TestExecutorSetAndSelect", session, "select now()", nil)
+
+	require.NoError(t, err)
+	session.SetSystemVariable("time_zone", "'+02:00'")
+
+	qrWith, err := e.Execute(ctx, nil, "TestExecutorSetAndSelect", session, "select now()", nil)
+	require.NoError(t, err)
+
+	assert.False(t, qr.Rows[0][0].Equal(qrWith.Rows[0][0]), "%v vs %v", qr.Rows[0][0].ToString(), qrWith.Rows[0][0].ToString())
+}

go/vt/vtgate/safe_session.go

@@ -23,6 +23,8 @@ import (
 	"sync"
 	"time"
 
+	"vitess.io/vitess/go/sqltypes"
+
 	"google.golang.org/protobuf/proto"
 
 	"vitess.io/vitess/go/mysql/datetime"
@@ -563,13 +565,21 @@ func (session *SafeSession) HasSystemVariables() (found bool) {
 
 func (session *SafeSession) TimeZone() *time.Location {
 	session.mu.Lock()
-	tz, ok := session.SystemVariables["time_zone"]
+	zoneSQL, ok := session.SystemVariables["time_zone"]
 	session.mu.Unlock()
 
 	if !ok {
 		return nil
 	}
+
+	tz, err := sqltypes.DecodeStringSQL(zoneSQL)
+	if err != nil {
+		return nil
+	}
+
 	loc, _ := datetime.ParseTimeZone(tz)
+	// it's safe to ignore the error - if we get an error, loc will be nil,
+	// and this is exactly the behaviour we want anyway
 	return loc
 }
 

go/vt/vtgate/safe_session_test.go

@@ -73,11 +73,11 @@ func TestTimeZone(t *testing.T) {
 		want string
 	}{
 		{
-			tz:   "Europe/Amsterdam",
+			tz:   "'Europe/Amsterdam'",
 			want: "Europe/Amsterdam",
 		},
 		{
-			tz:   "+02:00",
+			tz:   "'+02:00'",
 			want: "UTC+02:00",
 		},
 		{