Function TestRawBytesAreNotModified

driver_test.go:3279–3328

TestRawBytesAreNotModified checks for a race condition that arises when a query context is canceled while a user is calling rows.Scan. This is a more stringent test than the one proposed in https://github.com/golang/go/issues/23519. Here we're explicitly using `sql.RawBytes` to check the contents of

(t *testing.T)

// `sql.RawBytes` to check the contents of our internal buffers are not modified after an implicit
// call to `Rows.Close`, so Context cancellation should **not** invalidate the backing buffers.
func TestRawBytesAreNotModified(t *testing.T) {
	const blob = "abcdefghijklmnop"
	const contextRaceIterations = 20
	const blobSize = defaultBufSize * 3 / 4 // Second row overwrites first row.
	const insertRows = 4

	var sqlBlobs = [2]string{
		strings.Repeat(blob, blobSize/len(blob)),
		strings.Repeat(strings.ToUpper(blob), blobSize/len(blob)),
	}

	runTests(t, dsn, func(dbt *DBTest) {
		dbt.mustExec("CREATE TABLE test (id int, value BLOB) CHARACTER SET utf8")
		for i := range insertRows {
			dbt.mustExec("INSERT INTO test VALUES (?, ?)", i+1, sqlBlobs[i&1])
		}

		for i := range contextRaceIterations {
			func() {
				ctx, cancel := context.WithCancel(context.Background())
				defer cancel()

				rows, err := dbt.db.QueryContext(ctx, `SELECT id, value FROM test`)
				if err != nil {
					dbt.Fatal(err)
				}
				defer rows.Close()

				var b int
				var raw sql.RawBytes
				if !rows.Next() {
					dbt.Fatal("expected at least one row")
				}
				if err := rows.Scan(&b, &raw); err != nil {
					dbt.Fatal(err)
				}

				before := string(raw)
				// Ensure cancelling the query does not corrupt the contents of `raw`
				cancel()
				time.Sleep(time.Microsecond * 100)
				after := string(raw)

				if before != after {
					dbt.Fatalf("the backing storage for sql.RawBytes has been modified (i=%v)", i)
				}
			}()
		}
	})
}

var _ driver.DriverContext = &MySQLDriver{}