1 // Copyright 2017 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 cryptobyte contains types that help with parsing and constructing
6 // length-prefixed, binary messages, including ASN.1 DER. (The asn1 subpackage
7 // contains useful ASN.1 constants.)
8 //
9 // The String type is for parsing. It wraps a []byte slice and provides helper
10 // functions for consuming structures, value by value.
11 //
12 // The Builder type is for constructing messages. It providers helper functions
13 // for appending values and also for appending length-prefixed submessages –
14 // without having to worry about calculating the length prefix ahead of time.
15 //
16 // See the documentation and examples for the Builder and String types to get
17 // started.
18 package cryptobyte
19 20 // String represents a string of bytes. It provides methods for parsing
21 // fixed-length and length-prefixed values from it.
22 type String []byte
23 24 // read advances a String by n bytes and returns them. If less than n bytes
25 // remain, it returns nil.
26 func (s *String) read(n int) []byte {
27 if len(*s) < n || n < 0 {
28 return nil
29 }
30 v := (*s)[:n]
31 *s = (*s)[n:]
32 return v
33 }
34 35 // Skip advances the String by n byte and reports whether it was successful.
36 func (s *String) Skip(n int) bool {
37 return s.read(n) != nil
38 }
39 40 // ReadUint8 decodes an 8-bit value into out and advances over it.
41 // It reports whether the read was successful.
42 func (s *String) ReadUint8(out *uint8) bool {
43 v := s.read(1)
44 if v == nil {
45 return false
46 }
47 *out = uint8(v[0])
48 return true
49 }
50 51 // ReadUint16 decodes a big-endian, 16-bit value into out and advances over it.
52 // It reports whether the read was successful.
53 func (s *String) ReadUint16(out *uint16) bool {
54 v := s.read(2)
55 if v == nil {
56 return false
57 }
58 *out = uint16(v[0])<<8 | uint16(v[1])
59 return true
60 }
61 62 // ReadUint24 decodes a big-endian, 24-bit value into out and advances over it.
63 // It reports whether the read was successful.
64 func (s *String) ReadUint24(out *uint32) bool {
65 v := s.read(3)
66 if v == nil {
67 return false
68 }
69 *out = uint32(v[0])<<16 | uint32(v[1])<<8 | uint32(v[2])
70 return true
71 }
72 73 // ReadUint32 decodes a big-endian, 32-bit value into out and advances over it.
74 // It reports whether the read was successful.
75 func (s *String) ReadUint32(out *uint32) bool {
76 v := s.read(4)
77 if v == nil {
78 return false
79 }
80 *out = uint32(v[0])<<24 | uint32(v[1])<<16 | uint32(v[2])<<8 | uint32(v[3])
81 return true
82 }
83 84 // ReadUint48 decodes a big-endian, 48-bit value into out and advances over it.
85 // It reports whether the read was successful.
86 func (s *String) ReadUint48(out *uint64) bool {
87 v := s.read(6)
88 if v == nil {
89 return false
90 }
91 *out = uint64(v[0])<<40 | uint64(v[1])<<32 | uint64(v[2])<<24 | uint64(v[3])<<16 | uint64(v[4])<<8 | uint64(v[5])
92 return true
93 }
94 95 // ReadUint64 decodes a big-endian, 64-bit value into out and advances over it.
96 // It reports whether the read was successful.
97 func (s *String) ReadUint64(out *uint64) bool {
98 v := s.read(8)
99 if v == nil {
100 return false
101 }
102 *out = uint64(v[0])<<56 | uint64(v[1])<<48 | uint64(v[2])<<40 | uint64(v[3])<<32 | uint64(v[4])<<24 | uint64(v[5])<<16 | uint64(v[6])<<8 | uint64(v[7])
103 return true
104 }
105 106 func (s *String) readUnsigned(out *uint32, length int) bool {
107 v := s.read(length)
108 if v == nil {
109 return false
110 }
111 var result uint32
112 for i := 0; i < length; i++ {
113 result <<= 8
114 result |= uint32(v[i])
115 }
116 *out = result
117 return true
118 }
119 120 func (s *String) readLengthPrefixed(lenLen int, outChild *String) bool {
121 lenBytes := s.read(lenLen)
122 if lenBytes == nil {
123 return false
124 }
125 var length uint32
126 for _, b := range lenBytes {
127 length = length << 8
128 length = length | uint32(b)
129 }
130 v := s.read(int(length))
131 if v == nil {
132 return false
133 }
134 *outChild = v
135 return true
136 }
137 138 // ReadUint8LengthPrefixed reads the content of an 8-bit length-prefixed value
139 // into out and advances over it. It reports whether the read was successful.
140 func (s *String) ReadUint8LengthPrefixed(out *String) bool {
141 return s.readLengthPrefixed(1, out)
142 }
143 144 // ReadUint16LengthPrefixed reads the content of a big-endian, 16-bit
145 // length-prefixed value into out and advances over it. It reports whether the
146 // read was successful.
147 func (s *String) ReadUint16LengthPrefixed(out *String) bool {
148 return s.readLengthPrefixed(2, out)
149 }
150 151 // ReadUint24LengthPrefixed reads the content of a big-endian, 24-bit
152 // length-prefixed value into out and advances over it. It reports whether
153 // the read was successful.
154 func (s *String) ReadUint24LengthPrefixed(out *String) bool {
155 return s.readLengthPrefixed(3, out)
156 }
157 158 // ReadBytes reads n bytes into out and advances over them. It reports
159 // whether the read was successful.
160 func (s *String) ReadBytes(out *[]byte, n int) bool {
161 v := s.read(n)
162 if v == nil {
163 return false
164 }
165 *out = v
166 return true
167 }
168 169 // CopyBytes copies len(out) bytes into out and advances over them. It reports
170 // whether the copy operation was successful
171 func (s *String) CopyBytes(out []byte) bool {
172 n := len(out)
173 v := s.read(n)
174 if v == nil {
175 return false
176 }
177 return copy(out, v) == n
178 }
179 180 // Empty reports whether the string does not contain any bytes.
181 func (s String) Empty() bool {
182 return len(s) == 0
183 }
184