Bitcoin Core  0.20.99
P2P Digital Currency
univalue_utffilter.h
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1 // Copyright 2016 Wladimir J. van der Laan
2 // Distributed under the MIT software license, see the accompanying
3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
4 #ifndef UNIVALUE_UTFFILTER_H
5 #define UNIVALUE_UTFFILTER_H
6 
7 #include <string>
8 
14 {
15 public:
16  explicit JSONUTF8StringFilter(std::string &s):
17  str(s), is_valid(true), codepoint(0), state(0), surpair(0)
18  {
19  }
20  // Write single 8-bit char (may be part of UTF-8 sequence)
21  void push_back(unsigned char ch)
22  {
23  if (state == 0) {
24  if (ch < 0x80) // 7-bit ASCII, fast direct pass-through
25  str.push_back(ch);
26  else if (ch < 0xc0) // Mid-sequence character, invalid in this state
27  is_valid = false;
28  else if (ch < 0xe0) { // Start of 2-byte sequence
29  codepoint = (ch & 0x1f) << 6;
30  state = 6;
31  } else if (ch < 0xf0) { // Start of 3-byte sequence
32  codepoint = (ch & 0x0f) << 12;
33  state = 12;
34  } else if (ch < 0xf8) { // Start of 4-byte sequence
35  codepoint = (ch & 0x07) << 18;
36  state = 18;
37  } else // Reserved, invalid
38  is_valid = false;
39  } else {
40  if ((ch & 0xc0) != 0x80) // Not a continuation, invalid
41  is_valid = false;
42  state -= 6;
43  codepoint |= (ch & 0x3f) << state;
44  if (state == 0)
46  }
47  }
48  // Write codepoint directly, possibly collating surrogate pairs
49  void push_back_u(unsigned int codepoint_)
50  {
51  if (state) // Only accept full codepoints in open state
52  is_valid = false;
53  if (codepoint_ >= 0xD800 && codepoint_ < 0xDC00) { // First half of surrogate pair
54  if (surpair) // Two subsequent surrogate pair openers - fail
55  is_valid = false;
56  else
57  surpair = codepoint_;
58  } else if (codepoint_ >= 0xDC00 && codepoint_ < 0xE000) { // Second half of surrogate pair
59  if (surpair) { // Open surrogate pair, expect second half
60  // Compute code point from UTF-16 surrogate pair
61  append_codepoint(0x10000 | ((surpair - 0xD800)<<10) | (codepoint_ - 0xDC00));
62  surpair = 0;
63  } else // Second half doesn't follow a first half - fail
64  is_valid = false;
65  } else {
66  if (surpair) // First half of surrogate pair not followed by second - fail
67  is_valid = false;
68  else
69  append_codepoint(codepoint_);
70  }
71  }
72  // Check that we're in a state where the string can be ended
73  // No open sequences, no open surrogate pairs, etc
74  bool finalize()
75  {
76  if (state || surpair)
77  is_valid = false;
78  return is_valid;
79  }
80 private:
81  std::string &str;
82  bool is_valid;
83  // Current UTF-8 decoding state
84  unsigned int codepoint;
85  int state; // Top bit to be filled in for next UTF-8 byte, or 0
86 
87  // Keep track of the following state to handle the following section of
88  // RFC4627:
89  //
90  // To escape an extended character that is not in the Basic Multilingual
91  // Plane, the character is represented as a twelve-character sequence,
92  // encoding the UTF-16 surrogate pair. So, for example, a string
93  // containing only the G clef character (U+1D11E) may be represented as
94  // "\uD834\uDD1E".
95  //
96  // Two subsequent \u.... may have to be replaced with one actual codepoint.
97  unsigned int surpair; // First half of open UTF-16 surrogate pair, or 0
98 
99  void append_codepoint(unsigned int codepoint_)
100  {
101  if (codepoint_ <= 0x7f)
102  str.push_back((char)codepoint_);
103  else if (codepoint_ <= 0x7FF) {
104  str.push_back((char)(0xC0 | (codepoint_ >> 6)));
105  str.push_back((char)(0x80 | (codepoint_ & 0x3F)));
106  } else if (codepoint_ <= 0xFFFF) {
107  str.push_back((char)(0xE0 | (codepoint_ >> 12)));
108  str.push_back((char)(0x80 | ((codepoint_ >> 6) & 0x3F)));
109  str.push_back((char)(0x80 | (codepoint_ & 0x3F)));
110  } else if (codepoint_ <= 0x1FFFFF) {
111  str.push_back((char)(0xF0 | (codepoint_ >> 18)));
112  str.push_back((char)(0x80 | ((codepoint_ >> 12) & 0x3F)));
113  str.push_back((char)(0x80 | ((codepoint_ >> 6) & 0x3F)));
114  str.push_back((char)(0x80 | (codepoint_ & 0x3F)));
115  }
116  }
117 };
118 
119 #endif
void append_codepoint(unsigned int codepoint_)
void push_back(unsigned char ch)
Filter that generates and validates UTF-8, as well as collates UTF-16 surrogate pairs as specified in...
void push_back_u(unsigned int codepoint_)
JSONUTF8StringFilter(std::string &s)