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ref: added functionality to escapeJSONstrings (ref: #5251) #5508

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ref: added functionality to escapeJSONstrings (ref: #5251) #5508

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ref: added functionality to escapeJSONstrings (ref: #5251)
DarkLord017 Feb 14, 2025
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DarkLord017 Feb 14, 2025
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47 changes: 47 additions & 0 deletions contracts/utils/Strings.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,15 @@ library Strings {

bytes16 private constant HEX_DIGITS = "0123456789abcdef";
uint8 private constant ADDRESS_LENGTH = 20;
uint256 constant SPECIAL_CHARS_LOOKUP =
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(1 << 8) | // backspace
(1 << 9) | // tab
(1 << 10) | // newline
(1 << 12) | // form feed
(1 << 13) | // carriage return
(1 << 34) | // double quote
(1 << 47) | // forward slash
(1 << 92); // backslash
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/**
* @dev The `value` string doesn't fit in the specified `length`.
Expand Down Expand Up @@ -438,4 +447,42 @@ library Strings {
value := mload(add(buffer, add(0x20, offset)))
}
}

function _escapeJsonString(string memory input) private pure returns (string memory) {
bytes memory buffer = bytes(input);
bytes memory output = new bytes(buffer.length * 2); // Allocate max possible space
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I'm worried this allocated a lot of memory that is not freed. This is quite expensive. Alternatives are:

  • count number of "extra chars" in a loop, and allocate the right size directly
  • resize the output buffer without a copy, and move the free memory ptr, using assembly

uint256 outputLength = 0;

for (uint256 i; i < buffer.length; ) {
bytes1 char = buffer[i];

if ((SPECIAL_CHARS_LOOKUP & (1 << uint8(char))) != 0) {
output[outputLength++] = '\\';

if (char == 0x08) output[outputLength++] = 'b';
else if (char == 0x09) output[outputLength++] = 't';
else if (char == 0x0A) output[outputLength++] = 'n';
else if (char == 0x0C) output[outputLength++] = 'f';
else if (char == 0x0D) output[outputLength++] = 'r';
else if (char == 0x22) output[outputLength++] = '"';
else if (char == 0x2F) output[outputLength++] = '/';
else if (char == 0x5C) output[outputLength++] = '\\';
} else {
output[outputLength++] = char;
}

unchecked { ++i; }
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}

// Trim the output to the correct length
bytes memory finalOutput = new bytes(outputLength);
for (uint256 i = 0; i < outputLength; i++) {
finalOutput[i] = output[i];
}

return string(finalOutput);
}



}
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