Wladimir J. van der Laan
9 years ago
11 changed files with 181 additions and 37 deletions
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@@ -0,0 +1,119 @@
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// Copyright 2016 Wladimir J. van der Laan
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#ifndef UNIVALUE_UTFFILTER_H |
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#define UNIVALUE_UTFFILTER_H |
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#include <string> |
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/**
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* Filter that generates and validates UTF-8, as well as collates UTF-16 |
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* surrogate pairs as specified in RFC4627. |
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*/ |
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class JSONUTF8StringFilter |
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{ |
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public: |
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JSONUTF8StringFilter(std::string &s): |
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str(s), is_valid(true), codepoint(0), state(0), surpair(0) |
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{ |
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} |
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// Write single 8-bit char (may be part of UTF-8 sequence)
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void push_back(unsigned char ch) |
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{ |
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if (state == 0) { |
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if (ch < 0x80) // 7-bit ASCII, fast direct pass-through
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str.push_back(ch); |
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else if (ch < 0xc0) // Mid-sequence character, invalid in this state
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is_valid = false; |
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else if (ch < 0xe0) { // Start of 2-byte sequence
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codepoint = (ch & 0x1f) << 6; |
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state = 6; |
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} else if (ch < 0xf0) { // Start of 3-byte sequence
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codepoint = (ch & 0x0f) << 12; |
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state = 12; |
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} else if (ch < 0xf8) { // Start of 4-byte sequence
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codepoint = (ch & 0x07) << 18; |
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state = 18; |
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} else // Reserved, invalid
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is_valid = false; |
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} else { |
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if ((ch & 0xc0) != 0x80) // Not a continuation, invalid
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is_valid = false; |
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state -= 6; |
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codepoint |= (ch & 0x3f) << state; |
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if (state == 0) |
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push_back_u(codepoint); |
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} |
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} |
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// Write codepoint directly, possibly collating surrogate pairs
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void push_back_u(unsigned int codepoint) |
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{ |
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if (state) // Only accept full codepoints in open state
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is_valid = false; |
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if (codepoint >= 0xD800 && codepoint < 0xDC00) { // First half of surrogate pair
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if (surpair) // Two subsequent surrogate pair openers - fail
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is_valid = false; |
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else |
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surpair = codepoint; |
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} else if (codepoint >= 0xDC00 && codepoint < 0xE000) { // Second half of surrogate pair
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if (surpair) { // Open surrogate pair, expect second half
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// Compute code point from UTF-16 surrogate pair
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append_codepoint(0x10000 | ((surpair - 0xD800)<<10) | (codepoint - 0xDC00)); |
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surpair = 0; |
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} else // Second half doesn't follow a first half - fail
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is_valid = false; |
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} else { |
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if (surpair) // First half of surrogate pair not followed by second - fail
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is_valid = false; |
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else |
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append_codepoint(codepoint); |
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} |
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} |
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// Check that we're in a state where the string can be ended
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// No open sequences, no open surrogate pairs, etc
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bool finalize() |
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{ |
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if (state || surpair) |
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is_valid = false; |
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return is_valid; |
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} |
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private: |
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std::string &str; |
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bool is_valid; |
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// Current UTF-8 decoding state
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unsigned int codepoint; |
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int state; // Top bit to be filled in for next UTF-8 byte, or 0
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// Keep track of the following state to handle the following section of
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// RFC4627:
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//
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// To escape an extended character that is not in the Basic Multilingual
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// Plane, the character is represented as a twelve-character sequence,
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// encoding the UTF-16 surrogate pair. So, for example, a string
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// containing only the G clef character (U+1D11E) may be represented as
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// "\uD834\uDD1E".
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//
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// Two subsequent \u.... may have to be replaced with one actual codepoint.
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unsigned int surpair; // First half of open UTF-16 surrogate pair, or 0
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void append_codepoint(unsigned int codepoint) |
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{ |
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if (codepoint <= 0x7f) |
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str.push_back((char)codepoint); |
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else if (codepoint <= 0x7FF) { |
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str.push_back((char)(0xC0 | (codepoint >> 6))); |
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str.push_back((char)(0x80 | (codepoint & 0x3F))); |
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} else if (codepoint <= 0xFFFF) { |
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str.push_back((char)(0xE0 | (codepoint >> 12))); |
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str.push_back((char)(0x80 | ((codepoint >> 6) & 0x3F))); |
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str.push_back((char)(0x80 | (codepoint & 0x3F))); |
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} else if (codepoint <= 0x1FFFFF) { |
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str.push_back((char)(0xF0 | (codepoint >> 18))); |
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str.push_back((char)(0x80 | ((codepoint >> 12) & 0x3F))); |
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str.push_back((char)(0x80 | ((codepoint >> 6) & 0x3F))); |
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str.push_back((char)(0x80 | (codepoint & 0x3F))); |
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} |
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} |
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}; |
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#endif |
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