1 // Copyright 2009 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4 5 package asn1
6 7 import (
8 "strconv"
9 "bytes"
10 )
11 12 // ASN.1 objects have metadata preceding them:
13 // the tag: the type of the object
14 // a flag denoting if this object is compound or not
15 // the class type: the namespace of the tag
16 // the length of the object, in bytes
17 18 // Here are some standard tags and classes
19 20 // ASN.1 tags represent the type of the following object.
21 const (
22 TagBoolean = 1
23 TagInteger = 2
24 TagBitString = 3
25 TagOctetString = 4
26 TagNull = 5
27 TagOID = 6
28 TagEnum = 10
29 TagUTF8String = 12
30 TagSequence = 16
31 TagSet = 17
32 TagNumericString = 18
33 TagPrintableString = 19
34 TagT61String = 20
35 TagIA5String = 22
36 TagUTCTime = 23
37 TagGeneralizedTime = 24
38 TagGeneralString = 27
39 TagBMPString = 30
40 )
41 42 // ASN.1 class types represent the namespace of the tag.
43 const (
44 ClassUniversal = 0
45 ClassApplication = 1
46 ClassContextSpecific = 2
47 ClassPrivate = 3
48 )
49 50 type tagAndLength struct {
51 class, tag, length int
52 isCompound bool
53 }
54 55 // ASN.1 has IMPLICIT and EXPLICIT tags, which can be translated as "instead
56 // of" and "in addition to". When not specified, every primitive type has a
57 // default tag in the UNIVERSAL class.
58 //
59 // For example: a BIT STRING is tagged [UNIVERSAL 3] by default (although ASN.1
60 // doesn't actually have a UNIVERSAL keyword). However, by saying [IMPLICIT
61 // CONTEXT-SPECIFIC 42], that means that the tag is replaced by another.
62 //
63 // On the other hand, if it said [EXPLICIT CONTEXT-SPECIFIC 10], then an
64 // /additional/ tag would wrap the default tag. This explicit tag will have the
65 // compound flag set.
66 //
67 // (This is used in order to remove ambiguity with optional elements.)
68 //
69 // You can layer EXPLICIT and IMPLICIT tags to an arbitrary depth, however we
70 // don't support that here. We support a single layer of EXPLICIT or IMPLICIT
71 // tagging with tag strings on the fields of a structure.
72 73 // fieldParameters is the parsed representation of tag string from a structure field.
74 type fieldParameters struct {
75 optional bool // true iff the field is OPTIONAL
76 explicit bool // true iff an EXPLICIT tag is in use.
77 application bool // true iff an APPLICATION tag is in use.
78 private bool // true iff a PRIVATE tag is in use.
79 defaultValue *int64 // a default value for INTEGER typed fields (maybe nil).
80 tag *int // the EXPLICIT or IMPLICIT tag (maybe nil).
81 stringType int // the string tag to use when marshaling.
82 timeType int // the time tag to use when marshaling.
83 set bool // true iff this should be encoded as a SET
84 omitEmpty bool // true iff this should be omitted if empty when marshaling.
85 86 // Invariants:
87 // if explicit is set, tag is non-nil.
88 }
89 90 // Given a tag string with the format specified in the package comment,
91 // parseFieldParameters will parse it into a fieldParameters structure,
92 // ignoring unknown parts of the string.
93 func parseFieldParameters(str []byte) (ret fieldParameters) {
94 var part []byte
95 for len(str) > 0 {
96 part, str, _ = bytes.Cut(str, ",")
97 switch {
98 case part == "optional":
99 ret.optional = true
100 case part == "explicit":
101 ret.explicit = true
102 if ret.tag == nil {
103 var zero int
104 ret.tag = &zero
105 }
106 case part == "generalized":
107 ret.timeType = TagGeneralizedTime
108 case part == "utc":
109 ret.timeType = TagUTCTime
110 case part == "ia5":
111 ret.stringType = TagIA5String
112 case part == "printable":
113 ret.stringType = TagPrintableString
114 case part == "numeric":
115 ret.stringType = TagNumericString
116 case part == "utf8":
117 ret.stringType = TagUTF8String
118 case bytes.HasPrefix(part, "default:"):
119 i, err := strconv.ParseInt(part[8:], 10, 64)
120 if err == nil {
121 dv := i
122 ret.defaultValue = &dv
123 }
124 case bytes.HasPrefix(part, "tag:"):
125 i, err := strconv.Atoi(part[4:])
126 if err == nil {
127 tag := i
128 ret.tag = &tag
129 }
130 case part == "set":
131 ret.set = true
132 case part == "application":
133 ret.application = true
134 if ret.tag == nil {
135 var zero int
136 ret.tag = &zero
137 }
138 case part == "private":
139 ret.private = true
140 if ret.tag == nil {
141 var zero int
142 ret.tag = &zero
143 }
144 case part == "omitempty":
145 ret.omitEmpty = true
146 }
147 }
148 return
149 }
150 151 // getUniversalType returns the default ASN.1 tag number and expected compound
152 // flag for a type identified by its raw type code pointer.
153 func getUniversalType(t *_rawType) (matchAny bool, tagNumber int, isCompound, ok bool) {
154 switch t {
155 case _rawValueTC:
156 return true, -1, false, true
157 case _objectIdentifierTC:
158 return false, TagOID, false, true
159 case _bitStringTC:
160 return false, TagBitString, false, true
161 case _timeTC:
162 return false, TagUTCTime, false, true
163 case _enumeratedTC:
164 return false, TagEnum, false, true
165 case _bigIntPtrTC:
166 return false, TagInteger, false, true
167 }
168 switch t.kind() {
169 case akBool:
170 return false, TagBoolean, false, true
171 case akInt, akInt8, akInt16, akInt32, akInt64:
172 return false, TagInteger, false, true
173 case akStruct:
174 return false, TagSequence, true, true
175 case akSlice:
176 if t.elem().kind() == akUint8 {
177 return false, TagOctetString, false, true
178 }
179 if bytes.HasSuffix(t.typeName(), "SET") {
180 return false, TagSet, true, true
181 }
182 return false, TagSequence, true, true
183 case akBytes:
184 return false, TagPrintableString, false, true
185 }
186 return false, 0, false, false
187 }
188