summaryrefslogtreecommitdiffstats
path: root/src/encoding/asn1/common.go
blob: 40115df8b4b6aae141b603a360e1af6fb1761179 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package asn1

import (
	"reflect"
	"strconv"
	"strings"
)

// ASN.1 objects have metadata preceding them:
//   the tag: the type of the object
//   a flag denoting if this object is compound or not
//   the class type: the namespace of the tag
//   the length of the object, in bytes

// Here are some standard tags and classes

// ASN.1 tags represent the type of the following object.
const (
	TagBoolean         = 1
	TagInteger         = 2
	TagBitString       = 3
	TagOctetString     = 4
	TagNull            = 5
	TagOID             = 6
	TagEnum            = 10
	TagUTF8String      = 12
	TagSequence        = 16
	TagSet             = 17
	TagNumericString   = 18
	TagPrintableString = 19
	TagT61String       = 20
	TagIA5String       = 22
	TagUTCTime         = 23
	TagGeneralizedTime = 24
	TagGeneralString   = 27
	TagBMPString       = 30
)

// ASN.1 class types represent the namespace of the tag.
const (
	ClassUniversal       = 0
	ClassApplication     = 1
	ClassContextSpecific = 2
	ClassPrivate         = 3
)

type tagAndLength struct {
	class, tag, length int
	isCompound         bool
}

// ASN.1 has IMPLICIT and EXPLICIT tags, which can be translated as "instead
// of" and "in addition to". When not specified, every primitive type has a
// default tag in the UNIVERSAL class.
//
// For example: a BIT STRING is tagged [UNIVERSAL 3] by default (although ASN.1
// doesn't actually have a UNIVERSAL keyword). However, by saying [IMPLICIT
// CONTEXT-SPECIFIC 42], that means that the tag is replaced by another.
//
// On the other hand, if it said [EXPLICIT CONTEXT-SPECIFIC 10], then an
// /additional/ tag would wrap the default tag. This explicit tag will have the
// compound flag set.
//
// (This is used in order to remove ambiguity with optional elements.)
//
// You can layer EXPLICIT and IMPLICIT tags to an arbitrary depth, however we
// don't support that here. We support a single layer of EXPLICIT or IMPLICIT
// tagging with tag strings on the fields of a structure.

// fieldParameters is the parsed representation of tag string from a structure field.
type fieldParameters struct {
	optional     bool   // true iff the field is OPTIONAL
	explicit     bool   // true iff an EXPLICIT tag is in use.
	application  bool   // true iff an APPLICATION tag is in use.
	private      bool   // true iff a PRIVATE tag is in use.
	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.

	// Invariants:
	//   if explicit is set, tag is non-nil.
}

// Given a tag string with the format specified in the package comment,
// parseFieldParameters will parse it into a fieldParameters structure,
// ignoring unknown parts of the string.
func parseFieldParameters(str string) (ret fieldParameters) {
	var part string
	for len(str) > 0 {
		part, str, _ = strings.Cut(str, ",")
		switch {
		case part == "optional":
			ret.optional = true
		case part == "explicit":
			ret.explicit = true
			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":
			ret.stringType = TagPrintableString
		case part == "numeric":
			ret.stringType = TagNumericString
		case part == "utf8":
			ret.stringType = TagUTF8String
		case strings.HasPrefix(part, "default:"):
			i, err := strconv.ParseInt(part[8:], 10, 64)
			if err == nil {
				ret.defaultValue = new(int64)
				*ret.defaultValue = i
			}
		case strings.HasPrefix(part, "tag:"):
			i, err := strconv.Atoi(part[4:])
			if err == nil {
				ret.tag = new(int)
				*ret.tag = i
			}
		case part == "set":
			ret.set = true
		case part == "application":
			ret.application = true
			if ret.tag == nil {
				ret.tag = new(int)
			}
		case part == "private":
			ret.private = true
			if ret.tag == nil {
				ret.tag = new(int)
			}
		case part == "omitempty":
			ret.omitEmpty = true
		}
	}
	return
}

// Given a reflected Go type, getUniversalType returns the default tag number
// and expected compound flag.
func getUniversalType(t reflect.Type) (matchAny bool, tagNumber int, isCompound, ok bool) {
	switch t {
	case rawValueType:
		return true, -1, false, true
	case objectIdentifierType:
		return false, TagOID, false, true
	case bitStringType:
		return false, TagBitString, false, true
	case timeType:
		return false, TagUTCTime, false, true
	case enumeratedType:
		return false, TagEnum, false, true
	case bigIntType:
		return false, TagInteger, false, true
	}
	switch t.Kind() {
	case reflect.Bool:
		return false, TagBoolean, false, true
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return false, TagInteger, false, true
	case reflect.Struct:
		return false, TagSequence, true, true
	case reflect.Slice:
		if t.Elem().Kind() == reflect.Uint8 {
			return false, TagOctetString, false, true
		}
		if strings.HasSuffix(t.Name(), "SET") {
			return false, TagSet, true, true
		}
		return false, TagSequence, true, true
	case reflect.String:
		return false, TagPrintableString, false, true
	}
	return false, 0, false, false
}