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Fix bug in Bytes.lastIndexOf when array is empty and position is not 2²⁵⁶-1 #5797

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merged 8 commits into from
Jul 16, 2025
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Fix bug in Bytes.lastIndexOf when array is empty and position is not 2²⁵⁶-1 #5797

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c62f26d
Fix bug in Bytes.lastIndexOf when array is empty and position is not …
Amxx Jul 15, 2025
aa1cdb8
add changeset
Amxx Jul 15, 2025
29b1b35
branchless
Amxx Jul 15, 2025
edf974e
simplify fuzz cases
Amxx Jul 15, 2025
655c3c0
independant fuzz tests of and without pos
Amxx Jul 15, 2025
cfbb2e6
Update .changeset/witty-hats-flow.md
ernestognw Jul 15, 2025
df473af
use Math.saturatingAdd to more closelly match original syntax
Amxx Jul 16, 2025
6eb86f4
minimize changes
Amxx Jul 16, 2025
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5 changes: 5 additions & 0 deletions .changeset/witty-hats-flow.md
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@@ -0,0 +1,5 @@
---
'openzeppelin-solidity': patch
---

`Bytes`: Fix `lastIndexOf(bytes,byte,uint256)` with empty buffers and finite position to correctly return `type(uint256).max` instead of accessing uninitialized memory sections.
4 changes: 2 additions & 2 deletions contracts/utils/Bytes.sol
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Expand Up @@ -58,8 +58,8 @@ library Bytes {
function lastIndexOf(bytes memory buffer, bytes1 s, uint256 pos) internal pure returns (uint256) {
unchecked {
uint256 length = buffer.length;
// NOTE here we cannot do `i = Math.min(pos + 1, length)` because `pos + 1` could overflow
for (uint256 i = Math.min(pos, length - 1) + 1; i > 0; --i) {
uint256 end = Math.ternary(pos == type(uint256).max, length, Math.min(pos + 1, length));
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This might be more readable, and just as effective.

Suggested change
uint256 end = Math.ternary(pos == type(uint256).max, length, Math.min(pos + 1, length));
uint256 end = Math.min(Math.saturatingAdd(pos, 1), length);

@ernestognw @vesselinux @levi-sledd WDYT ?

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This is indeed equivalent and more readable.

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@Amxx Ahh, sorry to say but I find this to be even less readable haha. That's maybe because the overflow logic is buried inside the saturatingAdd thus making handling of edge cases less obvious. At the same time, I fully accept the arguments against my if-else suggestion.

The above said, I appreciate that readability is subjective, so feel free to adopt whichever of the two suggested variants the Contracts team like best. Indeed both are functionally equivalent and that's what matters at the end of the day.

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the overflow logic is buried inside the saturatingAdd thus making handling of edge cases less obvious

Interesting point of view. imo "burying the logic" should be the goal of the saturatingAdd function (and generally for any other library fn). In fact, I do prefer the saturatingAdd given I'd recommend using it to other developers in a similar situation as this.

for (uint256 i = end; i > 0; --i) {
if (bytes1(_unsafeReadBytesOffset(buffer, i - 1)) == s) {
return i - 1;
}
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70 changes: 70 additions & 0 deletions test/utils/Bytes.t.sol
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Expand Up @@ -9,6 +9,76 @@ import {Bytes} from "@openzeppelin/contracts/utils/Bytes.sol";
contract BytesTest is Test {
using Bytes for bytes;

// INDEX OF
function testIndexOf(bytes memory buffer, bytes1 s) public pure {
uint256 result = Bytes.indexOf(buffer, s);

if (buffer.length == 0) {
// Case 0: buffer is empty
assertEq(result, type(uint256).max);
} else if (result == type(uint256).max) {
// Case 1: search value could not be found
for (uint256 i = 0; i < buffer.length; ++i) assertNotEq(buffer[i], s);
} else {
// Case 2: search value was found
assertEq(buffer[result], s);
// search value is not present anywhere before the found location
for (uint256 i = 0; i < result; ++i) assertNotEq(buffer[i], s);
}
}

function testIndexOf(bytes memory buffer, bytes1 s, uint256 pos) public pure {
uint256 result = Bytes.indexOf(buffer, s, pos);

if (buffer.length == 0) {
// Case 0: buffer is empty
assertEq(result, type(uint256).max);
} else if (result == type(uint256).max) {
// Case 1: search value could not be found
for (uint256 i = pos; i < buffer.length; ++i) assertNotEq(buffer[i], s);
} else {
// Case 2: search value was found
assertEq(buffer[result], s);
// search value is not present anywhere before the found location
for (uint256 i = pos; i < result; ++i) assertNotEq(buffer[i], s);
}
}

function testLastIndexOf(bytes memory buffer, bytes1 s) public pure {
uint256 result = Bytes.lastIndexOf(buffer, s);

if (buffer.length == 0) {
// Case 0: buffer is empty
assertEq(result, type(uint256).max);
} else if (result == type(uint256).max) {
// Case 1: search value could not be found
for (uint256 i = 0; i < buffer.length; ++i) assertNotEq(buffer[i], s);
} else {
// Case 2: search value was found
assertEq(buffer[result], s);
// search value is not present anywhere after the found location
for (uint256 i = result + 1; i < buffer.length; ++i) assertNotEq(buffer[i], s);
}
}

function testLastIndexOf(bytes memory buffer, bytes1 s, uint256 pos) public pure {
uint256 result = Bytes.lastIndexOf(buffer, s, pos);

if (buffer.length == 0) {
// Case 0: buffer is empty
assertEq(result, type(uint256).max);
} else if (result == type(uint256).max) {
// Case 1: search value could not be found
for (uint256 i = 0; i <= Math.min(pos, buffer.length - 1); ++i) assertNotEq(buffer[i], s);
} else {
// Case 2: search value was found
assertEq(buffer[result], s);
// search value is not present anywhere after the found location
for (uint256 i = result + 1; i <= Math.min(pos, buffer.length - 1); ++i) assertNotEq(buffer[i], s);
}
}

// SLICES
function testSliceWithStartOnly(bytes memory buffer, uint256 start) public pure {
bytes memory originalBuffer = bytes.concat(buffer);
bytes memory result = buffer.slice(start);
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40 changes: 28 additions & 12 deletions test/utils/Bytes.test.js
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Expand Up @@ -28,39 +28,55 @@ describe('Bytes', function () {

describe('indexOf', function () {
it('first', async function () {
expect(await this.mock.$indexOf(lorem, ethers.toBeHex(present))).to.equal(lorem.indexOf(present));
await expect(this.mock.$indexOf(lorem, ethers.toBeHex(present))).to.eventually.equal(lorem.indexOf(present));
});

it('from index', async function () {
for (const start in Array(lorem.length + 10).fill()) {
const index = lorem.indexOf(present, start);
const result = index === -1 ? ethers.MaxUint256 : index;
expect(await this.mock.$indexOf(lorem, ethers.toBeHex(present), ethers.Typed.uint256(start))).to.equal(result);
await expect(
this.mock.$indexOf(lorem, ethers.toBeHex(present), ethers.Typed.uint256(start)),
).to.eventually.equal(result);
}
});

it('absent', async function () {
expect(await this.mock.$indexOf(lorem, ethers.toBeHex(absent))).to.equal(ethers.MaxUint256);
await expect(this.mock.$indexOf(lorem, ethers.toBeHex(absent))).to.eventually.equal(ethers.MaxUint256);
});

it('empty buffer', async function () {
await expect(this.mock.$indexOf('0x', '0x00')).to.eventually.equal(ethers.MaxUint256);
await expect(this.mock.$indexOf('0x', '0x00', ethers.Typed.uint256(17))).to.eventually.equal(ethers.MaxUint256);
});
});

describe('lastIndexOf', function () {
it('first', async function () {
expect(await this.mock.$lastIndexOf(lorem, ethers.toBeHex(present))).to.equal(lorem.lastIndexOf(present));
await expect(this.mock.$lastIndexOf(lorem, ethers.toBeHex(present))).to.eventually.equal(
lorem.lastIndexOf(present),
);
});

it('from index', async function () {
for (const start in Array(lorem.length + 10).fill()) {
const index = lorem.lastIndexOf(present, start);
const result = index === -1 ? ethers.MaxUint256 : index;
expect(await this.mock.$lastIndexOf(lorem, ethers.toBeHex(present), ethers.Typed.uint256(start))).to.equal(
result,
);
await expect(
this.mock.$lastIndexOf(lorem, ethers.toBeHex(present), ethers.Typed.uint256(start)),
).to.eventually.equal(result);
}
});

it('absent', async function () {
expect(await this.mock.$lastIndexOf(lorem, ethers.toBeHex(absent))).to.equal(ethers.MaxUint256);
await expect(this.mock.$lastIndexOf(lorem, ethers.toBeHex(absent))).to.eventually.equal(ethers.MaxUint256);
});

it('empty buffer', async function () {
await expect(this.mock.$lastIndexOf('0x', '0x00')).to.eventually.equal(ethers.MaxUint256);
await expect(this.mock.$lastIndexOf('0x', '0x00', ethers.Typed.uint256(17))).to.eventually.equal(
ethers.MaxUint256,
);
});
});

Expand All @@ -73,8 +89,8 @@ describe('Bytes', function () {
})) {
it(descr, async function () {
const result = ethers.hexlify(lorem.slice(start));
expect(await this.mock.$slice(lorem, start)).to.equal(result);
expect(await this.mock.$splice(lorem, start)).to.equal(result);
await expect(this.mock.$slice(lorem, start)).to.eventually.equal(result);
await expect(this.mock.$splice(lorem, start)).to.eventually.equal(result);
});
}
});
Expand All @@ -89,8 +105,8 @@ describe('Bytes', function () {
})) {
it(descr, async function () {
const result = ethers.hexlify(lorem.slice(start, end));
expect(await this.mock.$slice(lorem, start, ethers.Typed.uint256(end))).to.equal(result);
expect(await this.mock.$splice(lorem, start, ethers.Typed.uint256(end))).to.equal(result);
await expect(this.mock.$slice(lorem, start, ethers.Typed.uint256(end))).to.eventually.equal(result);
await expect(this.mock.$splice(lorem, start, ethers.Typed.uint256(end))).to.eventually.equal(result);
});
}
});
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