Increase domain for model.TimeAsEpochMicroseconds

Use `time.Unix()` instead of `time.UnixNano()` when the input exceeds the domain of `time.UnixNano()`

Signed-off-by: Prithvi Raj <p.r@uber.com>

model/time.go

@@ -26,7 +26,12 @@ func EpochMicrosecondsAsTime(ts uint64) time.Time {
 // TimeAsEpochMicroseconds converts time.Time to microseconds since epoch,
 // which is the format the StartTime field is stored in the Span.
 func TimeAsEpochMicroseconds(t time.Time) uint64 {
-	return uint64(t.UnixNano() / 1000)
+	if t.Year() > 1678 && t.Year() < 2262 {
+		// UnixNano's result is undefined if the Unix time in nanoseconds cannot be
+		// represented by an int64(less than year 1678 or greater than year 2262)
+		return uint64(t.UnixNano() / 1000)
+	}
+	return uint64(t.Unix() * 1e6)
 }
 
 // MicrosecondsAsDuration converts duration in microseconds to time.Duration value.

model/time_test.go

@@ -15,6 +15,7 @@
 package model_test
 
 import (
+	"math"
 	"testing"
 	"time"
 
@@ -39,3 +40,32 @@ func TestTimeZoneUTC(t *testing.T) {
 	ts := model.EpochMicrosecondsAsTime(10000100)
 	assert.Equal(t, time.UTC, ts.Location())
 }
+
+func TestTimeAsEpochMicroseconds(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    time.Time
+		expected uint64
+	}{
+		{
+			name:     "2018",
+			input:    time.Date(2018, 0, 0, 0, 0, 0, 0, time.UTC),
+			expected: 1512000000000000,
+		},
+		{
+			name:     "0",
+			input:    time.Unix(0, 0),
+			expected: 0,
+		},
+		{
+			name:     "large time",
+			input:    time.Date(math.MaxInt64, 0, 0, 0, 0, 0, 0, time.UTC),
+			expected: 18384542515693551616,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.expected, model.TimeAsEpochMicroseconds(tt.input))
+		})
+	}
+}