time: Add additional timestamp format for DateTime

Adds support for parsing DateTime timestamp formatted time similar to
RFC 3339, but without the `Z` character, nor UTC offset.

Fixes aws/aws-sdk-go-v2#1387

CHANGELOG.md

@@ -1,3 +1,11 @@
+# Release pending
+
+### Smithy Go Module
+
+* `time`: Add support for parsing additional DateTime timestamp format ([#324](https://github.com/aws/smithy-go/pull/324))
+  * Adds support for parsing DateTime timestamp formatted time similar to RFC 3339, but without the `Z` character, nor UTC offset.
+  * Fixes [#1387](https://github.com/aws/aws-sdk-go-v2/issues/1387)
+
 # Release v1.7.0
 
 ### Smithy Go Module

time/time.go

@@ -10,8 +10,9 @@ import (
 
 const (
 	// dateTimeFormat is a IMF-fixdate formatted RFC3339 section 5.6
-	dateTimeFormatInput  = "2006-01-02T15:04:05.999999999Z"
-	dateTimeFormatOutput = "2006-01-02T15:04:05.999Z"
+	dateTimeFormatInput    = "2006-01-02T15:04:05.999999999Z"
+	dateTimeFormatInputNoZ = "2006-01-02T15:04:05.999999999"
+	dateTimeFormatOutput   = "2006-01-02T15:04:05.999Z"
 
 	// httpDateFormat is a date time defined by RFC 7231#section-7.1.1.1
 	// IMF-fixdate with no UTC offset.
@@ -36,6 +37,7 @@ func FormatDateTime(value time.Time) string {
 func ParseDateTime(value string) (time.Time, error) {
 	return tryParse(value,
 		dateTimeFormatInput,
+		dateTimeFormatInputNoZ,
 		time.RFC3339Nano,
 		time.RFC3339,
 	)

time/time_test.go

@@ -19,6 +19,12 @@ func TestDateTime(t *testing.T) {
 				time.UTC),
 			SymmetricString: true,
 		},
+		"no offset, no Z": {
+			TimeString: "1985-04-12T23:20:50.524",
+			TimeValue: time.Date(1985, 4, 12, 23, 20, 50, int(524*time.Millisecond),
+				time.UTC),
+			SymmetricString: false,
+		},
 		"with negative offset": {
 			TimeString: "1985-04-12T23:20:50.52-07:00",
 			TimeValue: time.Date(1985, 4, 12, 23, 20, 50, int(520*time.Millisecond),