mirror of
https://github.com/liquidraver/ZephCore.git
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77 lines
1.9 KiB
C++
77 lines
1.9 KiB
C++
/*
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* SPDX-License-Identifier: MIT
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* ZephCore UTF8Helpers - UTF-8 aware truncation
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*
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* Ported from Arduino MeshCore 79dc1de6 ("fix: preserve UTF-8 advert names").
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*/
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#pragma once
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#include <stddef.h>
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#include <stdint.h>
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namespace mesh {
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inline bool isUtf8Continuation(uint8_t byte)
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{
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return (byte & 0xC0) == 0x80;
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}
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/**
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* Length of the longest prefix of `text` that is (a) valid UTF-8 and (b) no
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* longer than `max_bytes`. Never splits a multi-byte code point, and rejects
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* overlong encodings, surrogates and out-of-range 4-byte sequences.
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*
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* @returns byte count to copy; 0 if not even one code point fits
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*/
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inline size_t validUtf8PrefixLength(const char *text, size_t max_bytes)
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{
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if (text == nullptr) return 0;
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size_t offset = 0;
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while (text[offset] != '\0') {
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const uint8_t first = (uint8_t)text[offset];
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size_t sequence_length = 0;
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if (first <= 0x7F) {
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sequence_length = 1;
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} else if (first >= 0xC2 && first <= 0xDF) {
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sequence_length = 2;
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} else if (first >= 0xE0 && first <= 0xEF) {
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sequence_length = 3;
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} else if (first >= 0xF0 && first <= 0xF4) {
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sequence_length = 4;
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} else {
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break; /* continuation byte or overlong 2-byte lead */
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}
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if (offset + sequence_length > max_bytes) break;
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bool complete = true;
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for (size_t i = 1; i < sequence_length; i++) {
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if (text[offset + i] == '\0' ||
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!isUtf8Continuation((uint8_t)text[offset + i])) {
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complete = false;
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break;
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}
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}
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if (!complete) break;
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/* Reject overlong 3-byte forms and UTF-16 surrogates. */
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if (sequence_length == 3) {
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const uint8_t second = (uint8_t)text[offset + 1];
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if ((first == 0xE0 && second < 0xA0) ||
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(first == 0xED && second > 0x9F)) break;
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} else if (sequence_length == 4) {
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const uint8_t second = (uint8_t)text[offset + 1];
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if ((first == 0xF0 && second < 0x90) ||
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(first == 0xF4 && second > 0x8F)) break;
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}
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offset += sequence_length;
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}
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return offset;
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}
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} // namespace mesh
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