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>

5 files changed, 29 insertions, 3 deletions

diff --git a/src/encoding/asn1/asn1.go b/src/encoding/asn1/asn1.go
index aa99ca5cc5..7172c1c786 100644
--- a/src/encoding/asn1/asn1.go
+++ b/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:
diff --git a/src/encoding/asn1/asn1_test.go b/src/encoding/asn1/asn1_test.go
index 4e864d08ac..1a2ae2569f 100644
--- a/src/encoding/asn1/asn1_test.go
+++ b/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}},
 }
 
diff --git a/src/encoding/asn1/common.go b/src/encoding/asn1/common.go
index 33a117ece1..ab85e0496f 100644
--- a/src/encoding/asn1/common.go
+++ b/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":
diff --git a/src/encoding/asn1/marshal.go b/src/encoding/asn1/marshal.go
index bf92c04c9f..67a019db2d 100644
--- a/src/encoding/asn1/marshal.go
+++ b/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
 		}
 	}
diff --git a/src/encoding/asn1/marshal_test.go b/src/encoding/asn1/marshal_test.go
index 5b0115f28c..cdca8aa336 100644
--- a/src/encoding/asn1/marshal_test.go
+++ b/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"},