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.
18package cryptobyte // import "golang.org/x/crypto/cryptobyte"
19
20// String represents a string of bytes. It provides methods for parsing
21// fixed-length and length-prefixed values from it.
22type String []byte
23
24// read advances a String by n bytes and returns them. If less than n bytes
25// remain, it returns nil.
26func (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.
36func (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.
42func (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.
53func (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.
64func (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.
75func (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.
86func (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.
97func (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
106func (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
120func (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.
140func (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.
147func (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.
154func (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.
160func (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
171func (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.
181func (s String) Empty() bool {
182	return len(s) == 0
183}
184