StrSlice & Slice library for Solidity

• Types: StrSlice for strings, Slice for bytes, StrChar for characters
• Gas efficient
• Versioned releases, available for both foundry and hardhat
• Simple imports, you only need e.g. StrSlice and toSlice
• StrSlice enforces UTF-8 character boundaries; StrChar validates character encoding
• Clean, well-documented and thoroughly-tested source code
• Optional PRBTest extension with assertions like assertContains and assertLt for both slices and native bytes, string
• Slice and StrSlice are value types, not structs
• Low-level functions like memchr, memcmp, memmove etc

Install

Node

yarn add @dk1a/solidity-stringutils

Forge

forge install --no-commit dk1a/solidity-stringutils

StrSlice

import { StrSlice, toSlice } from "@dk1a/solidity-stringutils/src/StrSlice.sol";

using { toSlice } for string;

/// @dev Returns the content of brackets, or empty string if not found
function extractFromBrackets(string memory stuffInBrackets) pure returns (StrSlice extracted) {
    StrSlice s = stuffInBrackets.toSlice();
    bool found;

    (found, , s) = s.splitOnce(toSlice("("));
    if (!found) return toSlice("");

    (found, s, ) = s.rsplitOnce(toSlice(")"));
    if (!found) return toSlice("");

    return s;
}
/*
assertEq(
    extractFromBrackets("((1 + 2) + 3) + 4"),
    toSlice("(1 + 2) + 3")
);
*/

See ExamplesTest.

Internally StrSlice uses Slice and extends it with logic for multibyte UTF-8 where necessary.

Method	Description
len	length in bytes
isEmpty	true if len == 0
toString	copy slice contents to a new string
keccak	equal to keccak256(s.toString()), but cheaper
concatenate
add	Concatenate 2 slices into a new string
join	Join slice array on self as separator
compare
cmp	0 for eq, < 0 for lt, > 0 for gt
eq,ne	==, != (more efficient than cmp)
lt,lte	<, <=
gt,gte	>, >=
index
isCharBoundary	true if given index is an allowed boundary
get	get 1 UTF-8 character at given index
splitAt	(slice[:index], slice[index:])
getSubslice	slice[start:end]
search
find	index of the start of the first match
rfind	index of the start of the last match
	return type(uint256).max for no matches
contains	true if a match is found
startsWith	true if starts with pattern
endsWith	true if ends with pattern
modify
stripPrefix	returns subslice without the prefix
stripSuffix	returns subslice without the suffix
splitOnce	split into 2 subslices on the first match
rsplitOnce	split into 2 subslices on the last match
replacen	experimental replace n matches
	replacen requires 0 < pattern.len() <= to.len()
iterate
chars	character iterator over the slice
ascii
isAscii	true if all chars are ASCII
dangerous
asSlice	get underlying Slice
ptr	get memory pointer

Indexes are in bytes, not characters. Indexing methods revert if isCharBoundary is false.

StrCharsIter

Returned by chars method of StrSlice

import { StrSlice, toSlice, StrCharsIter } from "@dk1a/solidity-stringutils/src/StrSlice.sol";

using { toSlice } for string;

/// @dev Returns a StrSlice of `str` with the 2 first UTF-8 characters removed
/// reverts on invalid UTF8
function removeFirstTwoChars(string memory str) pure returns (StrSlice) {
    StrCharsIter memory chars = str.toSlice().chars();
    for (uint256 i; i < 2; i++) {
        if (chars.isEmpty()) break;
        chars.next();
    }
    return chars.asStr();
}
/*
assertEq(removeFirstTwoChars(unicode"📎!こんにちは"), unicode"こんにちは");
*/

Method	Description
asStr	get underlying StrSlice of the remainder
len	remainder length in bytes
isEmpty	true if len == 0
next	advance the iterator, return the next StrChar
nextBack	advance from the back, return the next StrChar
count	returns the number of UTF-8 characters
validateUtf8	returns true if the sequence is valid UTF-8
dangerous
unsafeNext	advance unsafely, return the next StrChar
unsafeCount	unsafely count chars, read the source for caveats
ptr	get memory pointer

count, validateUtf8, unsafeCount consume the iterator in O(n).

Safe methods revert on an invalid UTF-8 byte sequence.

unsafeNext does NOT check if the iterator is empty, may underflow! Does not revert on invalid UTF-8. If returned StrChar is invalid, it will have length 0. Otherwise length 1-4.

Internally next, unsafeNext, count all use _nextRaw. It's very efficient, but very unsafe and complicated. Read the source and import it separately if you need it.

StrChar

Represents a single UTF-8 encoded character. Internally it's bytes32 with leading byte at MSB.

It's returned by some methods of StrSlice and StrCharsIter.

Method	Description
len	character length in bytes
toBytes32	returns the underlying bytes32 value
toString	copy the character to a new string
toCodePoint	returns the unicode code point (ord in python)
cmp	0 for eq, < 0 for lt, > 0 for gt
eq,ne	==, !=
lt,lte	<, <=
gt,gte	>, >=
isValidUtf8	usually true
isAscii	true if the char is ASCII

Import StrChar__ (static function lib) to use StrChar__.fromCodePoint for code point to StrChar conversion.

len can return 0 only for invalid UTF-8 characters. But some invalid chars may have non-zero len! (use isValidUtf8 to check validity). Note that 0x00 is a valid 1-byte UTF-8 character, its len is 1.

isValidUtf8 can be false if the character was formed with an unsafe method (fromUnchecked, wrap).

Slice

import { Slice, toSlice } from "@dk1a/solidity-stringutils/src/Slice.sol";

using { toSlice } for bytes;

function findZeroByte(bytes memory b) pure returns (uint256 index) {
    return b.toSlice().find(
        bytes(hex"00").toSlice()
    );
}

See using {...} for Slice global in the source for a function summary. Many are shared between Slice and StrSlice, but there are differences.

Internally Slice has very minimal assembly, instead using memcpy, memchr, memcmp and others; if you need the low-level functions, see src/utils/.

Assertions (PRBTest extension)

import { PRBTest } from "@prb/test/src/PRBTest.sol";
import { Assertions } from "@dk1a/solidity-stringutils/src/test/Assertions.sol";

contract StrSliceTest is PRBTest, Assertions {
    function testContains() public {
        bytes memory b1 = "12345";
        bytes memory b2 = "3";
        assertContains(b1, b2);
    }

    function testLt() public {
        string memory s1 = "123";
        string memory s2 = "124";
        assertLt(s1, s2);
    }
}

You can completely ignore slices if all you want is e.g. assertContains for native bytes/string.

Acknowledgements

• Arachnid/solidity-stringutils - I basically wanted to make an updated version of solidity-stringutils
• rust - most similarities are in names and general structure; the implementation can't really be similar (solidity doesn't even have generics)
• paulrberg/prb-math - good template for solidity data structure libraries with using {...} for ... global
• brockelmore/memmove - good assembly memory management examples