Solidity Bytes Arrays Utils

Bytes tightly packed arrays' utility library for ethereum contracts written in Solidity.

The library lets you concatenate, slice and type cast bytes arrays both in memory and storage.

Given this library has an all-internal collection of methods it doesn't make sense to have it reside in the mainnet. Instead it will only be available on EPM as an installable package.

Important Fixes Changelog

2021-01-07

A bug regarding zero-length slices was disclosed by @MrChico following an audit to the Optimism codebase.

The exact bug happened under the following conditions: if memory slots higher then the current free-memory pointer were tainted before calling the slice method with a desired length of 0, the returned bytes array, instead of being a zero-length slice was an array of arbitrary length based on the values that previously populated that memory region.

Overall, the usage of zero-length slices should be pretty unusual and, as such, hopefully, this bug does not have far-reaching implications. Nonetheless, please update the library to the new version if you're using it in production.

TL;DR: if you're using the slice method with a length parameter of '0' in your codebase, please update to version 0.1.2 of the bytes library ASAP!

2020-11-01

There was a critical bug in the slice method, reported on an audit to a DXDao codebase.

Previously, no checks were being made on overflows of the _start and _length parameters since previous reviews of the codebase deemed this overflow "unexploitable" because of an inordinate expansion of memory (i.e., reading an immensely large memory offset causing huge memory expansion) resulting in an out-of-gas exception.

However, as noted in the review mentioned above, this is not the case. The slice method in versions <=0.9.0 actually allows for arbitrary kind of (i.e., it allows memory writes to very specific values) arbitrary memory writes _in the specific case where these parameters are user-supplied inputs and not hardcoded values (which is uncommon).

This made me realize that in permissioned blockchains where gas is also not a limiting factor this could become problematic in other methods and so I updated all typecasting-related methods to include new bound checks as well.

TL;DR: if you're using the slice method with user-supplied inputs in your codebase please update the bytes library immediately!

Version Notes:

• Starting from version v0.8.0 the versioning will change to follow compatible Solidity's compiler versions. This means that now the library will only compile on Solidity versions >=0.8.0 so, if you need <0.8.0 support for your project just use v0.1.2 of the library with:

$ truffle install [email protected]

or

$ npm install [email protected]

• Version v0.1.2 has a major bug fix.

• Version v0.1.1 has a critical bug fix.

• Version v0.9.0 now compiles with Solidity compilers 0.5.x and 0.6.x.

• Since version v0.0.7 the library will only compile on Solidity versions >0.4.22 so, if you need v0.4.x support for your project just use v0.0.6 of the library with:

$ truffle install [email protected]

or

$ npm install [email protected]

Usage

You can use the library here present by direct download and importing with:

import "BytesLib.sol";

or, if you have installed it from EPM (see below), with Truffle's specific paths:

import "bytes/BytesLib.sol";

Usage examples and API are more thoroughly explained below.

Also there's an extra library in there called AssertBytes (inside the same named file) which is compatible with Truffle's Solidity testing library Assert.sol event firing and so lets you now test bytes equalities/inequalities in your Solidity tests by just importing it in your .sol test files:

import "bytes/AssertBytes.sol";

and use the library AssertBytes much like they use Assert in Truffle's example.

EthPM

This library is published in EPM under the alias bytes

Installing it with Truffle

$ truffle install bytes

NPM

This library is published in NPM under the alias solidity-bytes-utils

Installing it with NPM

$ npm install solidity-bytes-utils

Importing it in your Solidity contract

import "solidity-bytes-utils/contracts/BytesLib.sol";

Contributing

Contributions are more than welcome in any way shape or form! 😄

TODOs:

• Two storage bytes arrays concatenation
• Slicing directly from storage
• Implement inline assembly functions for better readability

Testing

This project uses Truffle for tests. Truffle's version of solc needs to be at least 0.4.19 for the contracts to compile. If you encounter compilation errors, try:

$ cd /usr/local/lib/node_modules/truffle
$ npm install solc@latest

To run the tests, start a testrpc instance, then run truffle test.

API

• function concat(bytes memory _preBytes, bytes memory _postBytes) internal pure returns (bytes)

Concatenates two bytes arrays in memory and returns the concatenation result as another bytes array in memory.

• function concatStorage(bytes storage _preBytes, bytes memory _postBytes) internal pure

Concatenates a bytes array present in memory directly into the given storage location addressed by the _preBytes storage pointer.

• function slice(bytes _bytes, uint _start, uint _length) internal pure returns (bytes)

Takes a slice from a bytes array in memory of given length starting from _startth byte counting from the left-most one (0-based).

• function toAddress(bytes _bytes, uint _start) internal pure returns (address)

Takes a 20-byte-long sequence present in a bytes array in memory and returns that as an address (also checks for sufficient length).

• function toUint(bytes _bytes, uint _start) internal pure returns (uint256)

Takes a 32-byte-long sequence present in a bytes array in memory and returns that as an unsigned integer (also checks for sufficient length).

• function equal(bytes memory _preBytes, bytes memory _postBytes) internal view returns (bool)

Compares two bytes arrays in memory and returns the comparison result as a bool variable.

• function equalStorage(bytes storage _preBytes, bytes memory _postBytes) internal view returns (bool)

Compares a bytes array in storage against another bytes array in memory and returns the comparison result as a bool variable.

Examples

Ordered to mimic the above API section ordering:

contract MyContract {
	using BytesLib for bytes;

	function myFunc() {
		bytes memory _preBytes = hex"f00dfeed";
		bytes memory _postBytes = hex"f00dfeed";

		bytes memory concatBytes = _preBytes.concat(_postBytes);

		// concatBytes == 0xf00dfeedf00dfeed
	}
}

contract MyContract {
	using BytesLib for bytes;

	bytes storageBytes = hex"f00dfeed";

	function myFunc() {
		bytes memory _postBytes = hex"f00dfeed";

		storageBytes.concatStorage(_postBytes);

		// storageBytes == 0xf00dfeedf00dfeed
	}
}

contract MyContract {
	using BytesLib for bytes;

	function myFunc() {
		bytes memory memBytes = hex"f00dfeedaabbccddeeff";

		bytes memory slice1 = memBytes.slice(0, 2);
		bytes memory slice2 = memBytes.slice(2, 2);

		// slice1 == 0xf00d
		// slice2 == 0xfeed
	}
}

contract MyContract {
	using BytesLib for bytes;

	function myFunc() {
		bytes memory memBytes = hex"f00dfeed383Fa3B60f9B4AB7fBf6835d3c26C3765cD2B2e2f00dfeed";

		address addrFromBytes = memBytes.toAddress(4);

		// addrFromBytes == 0x383Fa3B60f9B4AB7fBf6835d3c26C3765cD2B2e2
	}
}

contract MyContract {
	using BytesLib for bytes;

	function myFunc() {
		bytes memory memBytes = hex"f00d0000000000000000000000000000000000000000000000000000000000000042feed";

		uint256 uintFromBytes = memBytes.toUint(2);

		// uintFromBytes == 42
	}
}

contract MyContract {
	using BytesLib for bytes;

	function myFunc() {
		bytes memory memBytes = hex"f00dfeed";
		bytes memory checkBytesTrue = hex"f00dfeed";
		bytes memory checkBytesFalse = hex"00000000";

		bool check1 = memBytes.equal(checkBytesTrue);
		bool check2 = memBytes.equal(checkBytesFalse);

		// check1 == true
		// check2 == false
	}
}

contract MyContract {
	using BytesLib for bytes;

	bytes storageBytes = hex"f00dfeed";

	function myFunc() {
		bytes memory checkBytesTrue = hex"f00dfeed";
		bytes memory checkBytesFalse = hex"00000000";

		bool check1 = storageBytes.equalStorage(checkBytesTrue);
		bool check2 = storageBytes.equalStorage(checkBytesFalse);

		// check1 == true
		// check2 == false
	}
}