57 lines
2.2 KiB
C
57 lines
2.2 KiB
C
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/*
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* Copyright (c) Meta Platforms, Inc. and affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*/
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#pragma once
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#include <vector>
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namespace facebook::react::jsinspector_modern {
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/**
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* Takes a vector of bytes representing a fragment of a UTF-8 string, and
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* removes the minimum number (0-3) of trailing bytes so that the remainder is
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* valid UTF-8. Useful for slicing binary data into UTF-8 strings.
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*
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* \param buffer Buffer to operate on - will be resized if necessary.
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*/
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inline void truncateToValidUTF8(std::vector<char>& buffer) {
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const auto length = buffer.size();
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// Ensure we don't cut a UTF-8 code point in the middle by removing any
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// trailing bytes representing an incomplete UTF-8 code point.
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// If the last byte is a UTF-8 first byte or continuation byte (topmost bit
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// is 1) (otherwise the last char is ASCII and we don't need to do
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// anything).
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if (length > 0 && (buffer[length - 1] & 0b10000000) == 0b10000000) {
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int continuationBytes = 0;
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// Find the first byte of the UTF-8 code point (topmost bits 11) and count
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// the number of continuation bytes following it.
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while ((buffer[length - continuationBytes - 1] & 0b11000000) !=
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0b11000000) {
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continuationBytes++;
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if (continuationBytes > 3 || continuationBytes >= length - 1) {
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throw std::runtime_error("Invalid UTF-8 sequence");
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}
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}
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char firstByteOfSequence = buffer[length - continuationBytes - 1];
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// Check for the special case that our original cut point was at the end
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// of a UTF-8 code-point, and therefore already valid. This will be the
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// case if the first byte indicates continuationBytes continuation bytes
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// should follow, i.e. its top bits are (1+continuationBytes) 1's followed
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// by a 0.
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char mask = static_cast<char>(0b11111000 << (3 - continuationBytes));
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char expectedBitsAfterMask = static_cast<char>(mask << 1);
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if (continuationBytes == 0 ||
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(firstByteOfSequence & mask) != expectedBitsAfterMask) {
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// Remove the trailing continuation bytes, if any, and the first byte.
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buffer.resize(length - (continuationBytes + 1));
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}
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}
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}
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} // namespace facebook::react::jsinspector_modern
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