gqlgen RFC3339 Timestamp Scalar

timestamp.go

package scalars

import (
	"errors"
	"io"
	"strconv"
	"time"

	"github.com/99designs/gqlgen/graphql"
)

// MarshalTimestamp returns a marshaler to convert a Go timestamp
// to a suitable GraphQL timestamp representation.
func MarshalTimestamp(t time.Time) graphql.Marshaler {
	return graphql.WriterFunc(func(w io.Writer) {
		io.WriteString(w, strconv.Quote(t.Format(time.RFC3339)))
	})
}

// UnmarshalTimestamp is used by GraphQL to unmarshal supplied timestamps
// into a Golang representation for further use internally.
func UnmarshalTimestamp(v interface{}) (time.Time, error) {
	if tmpStr, ok := v.(string); ok {
		return time.Parse(time.RFC3339, tmpStr)
	}

	return time.Time{}, errors.New("time should be a RFC3339 compliant ISO-8601 timestamp")
}

timestamp_test.go

package scalars

import (
	"strconv"
	"strings"
	"testing"
	"time"

	"github.com/stretchr/testify/require"
)

func TestMarshalTimestamp (t *testing.T) {
	now := time.Now()

	// Test that we can successfully marshal the timestamp
	buf := new(strings.Builder)
	MarshalTimestamp(now).MarshalGQL(buf)

	// Test that the marshaled result is as expected
	require.NotNil(t, buf)
	require.Equal(t, strconv.Quote(now.Format(time.RFC3339)), buf.String(), "marshaled time does not match expected time string")
}

func TestUnmarshalTimestamp (t *testing.T) {
	timeStr := "2021-04-05T21:03:14Z"

	// Unmarshal the timestamp from the RFC 3339 string
	unmarshalledTime, err := UnmarshalTimestamp(timeStr)
	require.Nil(t, err, "failed to unmarshal timestamp")

	// Compare the individual time components
	require.Equal(t, 2021, unmarshalledTime.Year())
	require.Equal(t, 04, (int)(unmarshalledTime.Month()))
	require.Equal(t, 05, unmarshalledTime.Day())
	require.Equal(t, 21, unmarshalledTime.Hour())
	require.Equal(t, 03, unmarshalledTime.Minute())
	require.Equal(t, 14, unmarshalledTime.Second())

	// Quick sanity check that it converts back to it's self correctly
	require.Equal(t, timeStr, unmarshalledTime.Format(time.RFC3339), "unmarshalled time does not convert back to it's self")
}