Add Bytes.concat

[Amxx]

Mentionned in https://github.com/OpenZeppelin/openzeppelin-contracts/pull/5680/files#diff-0399261b2cd954212dda0147b86044380b879ab21e1d1b89c564cb48f3552216R217

See #5680

PR Checklist

• Tests
• Documentation
• Changeset entry (run npx changeset add)

Summary by Sourcery

Introduce a new concat function in the Bytes library to merge multiple byte buffers into a single bytes value, with comprehensive tests and documentation.

New Features:

• Add Bytes.concat function to concatenate an array of byte buffers into one bytes object.

Documentation:

• Add NatSpec documentation for the new Bytes.concat function.

Tests:

• Add unit tests for concat covering empty arrays, single-item arrays, and multiple-item arrays.

Chores:

• Add changeset entry for a minor version bump.

[changeset-bot]

🦋 Changeset detected

Latest commit: bbda17f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
openzeppelin-solidity	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[sourcery-ai]

Reviewer's Guide

Introduces a new Bytes.concat function to merge an array of byte buffers into a single bytes object, along with targeted unit tests and a changeset entry.

Class diagram for the updated Bytes library with concat function

classDiagram
    class Bytes {
        <<library>>
        +concat(buffers: bytes[]) bytes
        +equal(a: bytes, b: bytes) bool
        ...
    }

Loading

Flow diagram for Bytes.concat function logic

flowchart TD
    A[Start] --> B[Initialize length = 0]
    B --> C[Loop over buffers to sum lengths]
    C --> D[Create result bytes of total length]
    D --> E[Set offset = 0x20]
    E --> F[Loop over buffers]
    F --> G[Copy buffer into result at offset]
    G --> H[Increment offset by buffer length]
    H --> I{All buffers processed?}
    I -- No --> F
    I -- Yes --> J[Return result]
    J --> K[End]

Loading

File-Level Changes

Change	Details	Files
Implement Bytes.concat utility	Sum lengths of all input buffers Allocate a new bytes array of the combined length Copy each input into the result using an assembly mcopy loop	contracts/utils/Bytes.sol
Add unit tests for concat	Verify empty array returns zero bytes Verify single item returns itself Verify multiple items match ethers.concat	test/utils/Bytes.test.js
Add changeset entry for concat	Document the new minor release for Bytes.concat	.changeset/old-memes-dress.md

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[sourcery-ai]

Hey there - I've reviewed your changes - here's some feedback:

• Consider wrapping the offset += input.length arithmetic inside an unchecked block to avoid redundant overflow checks and save gas.
• Add a test case where some buffers are empty and others are non‐empty (e.g. interleaved zero‐length elements) to ensure correct concatenation behavior in edge cases.
• Double‐check that the mcopy memory‐safe assembly macro is supported on all targeted Solidity compiler versions and consider providing a fallback memcpy implementation if not.

Prompt for AI Agents

Please address the comments from this code review:
## Overall Comments
- Consider wrapping the `offset += input.length` arithmetic inside an `unchecked` block to avoid redundant overflow checks and save gas.
- Add a test case where some buffers are empty and others are non‐empty (e.g. interleaved zero‐length elements) to ensure correct concatenation behavior in edge cases.
- Double‐check that the `mcopy` memory‐safe assembly macro is supported on all targeted Solidity compiler versions and consider providing a fallback memcpy implementation if not.

## Individual Comments

### Comment 1
<location> `contracts/utils/Bytes.sol:134` </location>
<code_context>
+    /**
+     * @dev Concatenate an array of bytes into a single bytes object.
+     *
+     * For fixed bytes types, we recommand using the solidity built-in `bytes.concat` or (equivalent)
+     *`abi.encodePacked`.
+     *
</code_context>

<issue_to_address>
Typo in documentation: 'recommand' should be 'recommend'.

Fixing the typo enhances documentation quality.
</issue_to_address>

<suggested_fix>
<<<<<<< SEARCH
     * For fixed bytes types, we recommand using the solidity built-in `bytes.concat` or (equivalent)
     *`abi.encodePacked`.
=======
     * For fixed bytes types, we recommend using the solidity built-in `bytes.concat` or (equivalent)
     *`abi.encodePacked`.
>>>>>>> REPLACE

</suggested_fix>

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[ernestognw]

Looks good.

I initially thought about this function to be in Arrays mimicking the Javascript's API for flatten. If you guys think this is a good approach, then it may be worth exploring.

[Amxx]

Javascript's flatten is "Array of Array => Array", which makes sens in the case of javascript because Arrays can contain multiple different types.

IMO, Buffer or Strings would be a better match to solidity's bytes than Array. In javascript, Array.flat does NOT merge strings or buffer, which would mean that this concat function (equivalent to ethers.concat) doesn't really match Array.flat.

Also IMO, this "bytes concatenate" function is more bytes specific then it is array specific. I guess that can be disputed, but I'm not sure it would make sens to have a similar function for arrays of uint256, or arrays of bytes32. It would make sens to have something similar for arrays of strings, but I would put that in Strings.sol, not in Array.sol.