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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 https://opensource.org/licenses/mit-license.php.
4 : : #ifndef BITCOIN_UNIVALUE_INCLUDE_UNIVALUE_UTFFILTER_H
5 : : #define BITCOIN_UNIVALUE_INCLUDE_UNIVALUE_UTFFILTER_H
6 : :
7 : : #include <string>
8 : :
9 : : /**
10 : : * Filter that generates and validates UTF-8, as well as collates UTF-16
11 : : * surrogate pairs as specified in RFC4627.
12 : : */
13 : : class JSONUTF8StringFilter
14 : : {
15 : : public:
16 : 15889 : explicit JSONUTF8StringFilter(std::string& s)
17 : 15889 : : str(s)
18 : : {
19 : 15889 : }
20 : : // Write single 8-bit char (may be part of UTF-8 sequence)
21 : 778633 : void push_back(unsigned char ch)
22 : : {
23 [ + + ]: 778633 : if (state == 0) {
24 [ + + ]: 778622 : if (ch < 0x80) // 7-bit ASCII, fast direct pass-through
25 : 778614 : str.push_back(ch);
26 [ + + ]: 8 : else if (ch < 0xc0) // Mid-sequence character, invalid in this state
27 : 3 : is_valid = false;
28 [ + + ]: 5 : else if (ch < 0xe0) { // Start of 2-byte sequence
29 : 1 : codepoint = (ch & 0x1f) << 6;
30 : 1 : state = 6;
31 [ + + ]: 4 : } else if (ch < 0xf0) { // Start of 3-byte sequence
32 : 1 : codepoint = (ch & 0x0f) << 12;
33 : 1 : state = 12;
34 [ + - ]: 3 : } else if (ch < 0xf8) { // Start of 4-byte sequence
35 : 3 : codepoint = (ch & 0x07) << 18;
36 : 3 : state = 18;
37 : : } else // Reserved, invalid
38 : 0 : is_valid = false;
39 : : } else {
40 [ - + ]: 11 : if ((ch & 0xc0) != 0x80) // Not a continuation, invalid
41 : 0 : is_valid = false;
42 : 11 : state -= 6;
43 : 11 : codepoint |= (ch & 0x3f) << state;
44 [ + + ]: 11 : if (state == 0)
45 : 4 : push_back_u(codepoint);
46 : : }
47 : 778633 : }
48 : : // Write codepoint directly, possibly collating surrogate pairs
49 : 54 : void push_back_u(unsigned int codepoint_)
50 : : {
51 [ - + ]: 54 : if (state) // Only accept full codepoints in open state
52 : 0 : is_valid = false;
53 [ + + ]: 54 : if (codepoint_ >= 0xD800 && codepoint_ < 0xDC00) { // First half of surrogate pair
54 [ - + ]: 2 : if (surpair) // Two subsequent surrogate pair openers - fail
55 : 0 : is_valid = false;
56 : : else
57 : 2 : surpair = codepoint_;
58 [ + + ]: 52 : } else if (codepoint_ >= 0xDC00 && codepoint_ < 0xE000) { // Second half of surrogate pair
59 [ + + ]: 2 : if (surpair) { // Open surrogate pair, expect second half
60 : : // Compute code point from UTF-16 surrogate pair
61 : 1 : append_codepoint(0x10000 | ((surpair - 0xD800)<<10) | (codepoint_ - 0xDC00));
62 : 1 : surpair = 0;
63 : : } else // Second half doesn't follow a first half - fail
64 : 1 : is_valid = false;
65 : : } else {
66 [ - + ]: 50 : if (surpair) // First half of surrogate pair not followed by second - fail
67 : 0 : is_valid = false;
68 : : else
69 : 50 : append_codepoint(codepoint_);
70 : : }
71 : 54 : }
72 : : // Check that we're in a state where the string can be ended
73 : : // No open sequences, no open surrogate pairs, etc
74 : 15881 : bool finalize()
75 : : {
76 [ + + ]: 15881 : if (state || surpair)
77 : 2 : is_valid = false;
78 [ + + ]: 15881 : return is_valid;
79 : : }
80 : : private:
81 : : std::string &str;
82 : : bool is_valid{true};
83 : : // Current UTF-8 decoding state
84 : : unsigned int codepoint{0};
85 : : int state{0}; // 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{0}; // First half of open UTF-16 surrogate pair, or 0
98 : :
99 : 51 : void append_codepoint(unsigned int codepoint_)
100 : : {
101 [ + + ]: 51 : if (codepoint_ <= 0x7f)
102 : 32 : str.push_back((char)codepoint_);
103 [ + + ]: 19 : else if (codepoint_ <= 0x7FF) {
104 : 3 : str.push_back((char)(0xC0 | (codepoint_ >> 6)));
105 : 3 : str.push_back((char)(0x80 | (codepoint_ & 0x3F)));
106 [ + + ]: 16 : } else if (codepoint_ <= 0xFFFF) {
107 : 13 : str.push_back((char)(0xE0 | (codepoint_ >> 12)));
108 : 13 : str.push_back((char)(0x80 | ((codepoint_ >> 6) & 0x3F)));
109 : 13 : str.push_back((char)(0x80 | (codepoint_ & 0x3F)));
110 [ + - ]: 3 : } else if (codepoint_ <= 0x1FFFFF) {
111 : 3 : str.push_back((char)(0xF0 | (codepoint_ >> 18)));
112 : 3 : str.push_back((char)(0x80 | ((codepoint_ >> 12) & 0x3F)));
113 : 3 : str.push_back((char)(0x80 | ((codepoint_ >> 6) & 0x3F)));
114 : 3 : str.push_back((char)(0x80 | (codepoint_ & 0x3F)));
115 : : }
116 : 51 : }
117 : : };
118 : :
119 : : #endif // BITCOIN_UNIVALUE_INCLUDE_UNIVALUE_UTFFILTER_H
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