encoding/asn1: Improved control of flags and times

This change corrects the serialization of asn1.Flag values, so that
when set, they serialize to an empty value, and when unset, they are
omitted. It also adds a format parameter that allows calling code
to control whether time.Time values are serialized as UTCTime or
GeneralizedTime.

Change-Id: I6d97abf009ea317338dab30c80f35a2de7e07104
Reviewed-on: https://go-review.googlesource.com/5970
Reviewed-by: Adam Langley <agl@golang.org>
Run-TryBot: Adam Langley <agl@golang.org>

src/encoding/asn1/asn1.go

@@ -579,6 +579,8 @@ func parseField(v reflect.Value, bytes []byte, initOffset int, params fieldParam
 				result, err = parseObjectIdentifier(innerBytes)
 			case tagUTCTime:
 				result, err = parseUTCTime(innerBytes)
+			case tagGeneralizedTime:
+				result, err = parseGeneralizedTime(innerBytes)
 			case tagOctetString:
 				result = innerBytes
 			default:

src/encoding/asn1/asn1_test.go

@@ -358,6 +358,8 @@ func newBool(b bool) *bool { return &b }
 var parseFieldParametersTestData []parseFieldParametersTest = []parseFieldParametersTest{
 	{"", fieldParameters{}},
 	{"ia5", fieldParameters{stringType: tagIA5String}},
+	{"generalized", fieldParameters{timeType: tagGeneralizedTime}},
+	{"utc", fieldParameters{timeType: tagUTCTime}},
 	{"printable", fieldParameters{stringType: tagPrintableString}},
 	{"optional", fieldParameters{optional: true}},
 	{"explicit", fieldParameters{explicit: true, tag: new(int)}},
@@ -366,7 +368,7 @@ var parseFieldParametersTestData []parseFieldParametersTest = []parseFieldParame
 	{"default:42", fieldParameters{defaultValue: newInt64(42)}},
 	{"tag:17", fieldParameters{tag: newInt(17)}},
 	{"optional,explicit,default:42,tag:17", fieldParameters{optional: true, explicit: true, defaultValue: newInt64(42), tag: newInt(17)}},
-	{"optional,explicit,default:42,tag:17,rubbish1", fieldParameters{true, true, false, newInt64(42), newInt(17), 0, false, false}},
+	{"optional,explicit,default:42,tag:17,rubbish1", fieldParameters{true, true, false, newInt64(42), newInt(17), 0, 0, false, false}},
 	{"set", fieldParameters{set: true}},
 }
 

src/encoding/asn1/common.go

@@ -74,6 +74,7 @@ type fieldParameters struct {
 	defaultValue *int64 // a default value for INTEGER typed fields (maybe nil).
 	tag          *int   // the EXPLICIT or IMPLICIT tag (maybe nil).
 	stringType   int    // the string tag to use when marshaling.
+	timeType     int    // the time tag to use when marshaling.
 	set          bool   // true iff this should be encoded as a SET
 	omitEmpty    bool   // true iff this should be omitted if empty when marshaling.
 
@@ -94,6 +95,10 @@ func parseFieldParameters(str string) (ret fieldParameters) {
 			if ret.tag == nil {
 				ret.tag = new(int)
 			}
+		case part == "generalized":
+			ret.timeType = tagGeneralizedTime
+		case part == "utc":
+			ret.timeType = tagUTCTime
 		case part == "ia5":
 			ret.stringType = tagIA5String
 		case part == "printable":

src/encoding/asn1/marshal.go

@@ -410,9 +410,11 @@ func stripTagAndLength(in []byte) []byte {
 
 func marshalBody(out *forkableWriter, value reflect.Value, params fieldParameters) (err error) {
 	switch value.Type() {
+	case flagType:
+		return nil
 	case timeType:
 		t := value.Interface().(time.Time)
-		if outsideUTCRange(t) {
+		if params.timeType == tagGeneralizedTime || outsideUTCRange(t) {
 			return marshalGeneralizedTime(out, t)
 		} else {
 			return marshalUTCTime(out, t)
@@ -552,6 +554,10 @@ func marshalField(out *forkableWriter, v reflect.Value, params fieldParameters)
 	}
 	class := classUniversal
 
+	if params.timeType != 0 && tag != tagUTCTime {
+		return StructuralError{"explicit time type given to non-time member"}
+	}
+
 	if params.stringType != 0 && tag != tagPrintableString {
 		return StructuralError{"explicit string type given to non-string member"}
 	}
@@ -575,7 +581,7 @@ func marshalField(out *forkableWriter, v reflect.Value, params fieldParameters)
 			tag = params.stringType
 		}
 	case tagUTCTime:
-		if outsideUTCRange(v.Interface().(time.Time)) {
+		if params.timeType == tagGeneralizedTime || outsideUTCRange(v.Interface().(time.Time)) {
 			tag = tagGeneralizedTime
 		}
 	}

src/encoding/asn1/marshal_test.go

@@ -42,6 +42,14 @@ type explicitTagTest struct {
 	A int `asn1:"explicit,tag:5"`
 }
 
+type flagTest struct {
+	A Flag `asn1:"tag:0,optional"`
+}
+
+type generalizedTimeTest struct {
+	A time.Time `asn1:"generalized"`
+}
+
 type ia5StringTest struct {
 	A string `asn1:"ia5"`
 }
@@ -92,10 +100,13 @@ var marshalTests = []marshalTest{
 	{[]byte{1, 2, 3}, "0403010203"},
 	{implicitTagTest{64}, "3003850140"},
 	{explicitTagTest{64}, "3005a503020140"},
+	{flagTest{true}, "30028000"},
+	{flagTest{false}, "3000"},
 	{time.Unix(0, 0).UTC(), "170d3730303130313030303030305a"},
 	{time.Unix(1258325776, 0).UTC(), "170d3039313131353232353631365a"},
 	{time.Unix(1258325776, 0).In(PST), "17113039313131353134353631362d30383030"},
 	{farFuture(), "180f32313030303430353132303130315a"},
+	{generalizedTimeTest{time.Unix(1258325776, 0).UTC()}, "3011180f32303039313131353232353631365a"},
 	{BitString{[]byte{0x80}, 1}, "03020780"},
 	{BitString{[]byte{0x81, 0xf0}, 12}, "03030481f0"},
 	{ObjectIdentifier([]int{1, 2, 3, 4}), "06032a0304"},