Add Bytes.splice, an inplace variant of Buffer.slice (#5733)

Co-authored-by: James Toussaint <33313130+james-toussaint@users.noreply.github.com>
Co-authored-by: ernestognw <ernestognw@gmail.com>

Author: 3 people

.changeset/afraid-chicken-attack.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`Bytes`: Add `splice(bytes,uint256)` and `splice(bytes,uint256,uint256)` functions that move a specified range of bytes to the start of the buffer and truncate it in place, as an alternative to `slice`.

contracts/utils/Bytes.sol

@@ -80,7 +80,7 @@ library Bytes {
 
     /**
      * @dev Copies the content of `buffer`, from `start` (included) to `end` (excluded) into a new bytes object in
-     * memory.
+     * memory. The `end` argument is truncated to the length of the `buffer`.
      *
      * NOTE: replicates the behavior of https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice[Javascript's `Array.slice`]
      */
@@ -100,6 +100,36 @@ library Bytes {
     }
 
     /**
+     * @dev Moves the content of `buffer`, from `start` (included) to the end of `buffer` to the start of that buffer.
+     *
+     * NOTE: This function modifies the provided buffer in place. If you need to preserve the original buffer, use {slice} instead
+     */
+    function splice(bytes memory buffer, uint256 start) internal pure returns (bytes memory) {
+        return splice(buffer, start, buffer.length);
+    }
+
+    /**
+     * @dev Moves the content of `buffer`, from `start` (included) to end (excluded) to the start of that buffer. The
+     * `end` argument is truncated to the length of the `buffer`.
+     *
+     * NOTE: This function modifies the provided buffer in place. If you need to preserve the original buffer, use {slice} instead
+     */
+    function splice(bytes memory buffer, uint256 start, uint256 end) internal pure returns (bytes memory) {
+        // sanitize
+        uint256 length = buffer.length;
+        end = Math.min(end, length);
+        start = Math.min(start, end);
+
+        // allocate and copy
+        assembly ("memory-safe") {
+            mcopy(add(buffer, 0x20), add(add(buffer, 0x20), start), sub(end, start))
+            mstore(buffer, sub(end, start))
+        }
+
+        return buffer;
+    }
+
+    /*
      * @dev Reverses the byte order of a bytes32 value, converting between little-endian and big-endian.
      * Inspired in https://graphics.stanford.edu/~seander/bithacks.html#ReverseParallel[Reverse Parallel]
      */

test/utils/Bytes.t.sol

@@ -3,9 +3,84 @@
 pragma solidity ^0.8.20;
 
 import {Test} from "forge-std/Test.sol";
+import {Math} from "@openzeppelin/contracts/utils/math/Math.sol";
 import {Bytes} from "@openzeppelin/contracts/utils/Bytes.sol";
 
 contract BytesTest is Test {
+    using Bytes for bytes;
+
+    function testSliceWithStartOnly(bytes memory buffer, uint256 start) public pure {
+        bytes memory originalBuffer = bytes.concat(buffer);
+        bytes memory result = buffer.slice(start);
+
+        // Original buffer was not modified
+        assertEq(buffer, originalBuffer);
+
+        // Should return bytes from start to end
+        assertEq(result.length, Math.saturatingSub(buffer.length, start));
+
+        // Verify content matches
+        for (uint256 i = 0; i < result.length; ++i) {
+            assertEq(result[i], buffer[start + i]);
+        }
+    }
+
+    function testSlice(bytes memory buffer, uint256 start, uint256 end) public pure {
+        bytes memory originalBuffer = bytes.concat(buffer);
+        bytes memory result = buffer.slice(start, end);
+
+        // Original buffer was not modified
+        assertEq(buffer, originalBuffer);
+
+        // Calculate expected bounds after sanitization
+        uint256 sanitizedEnd = Math.min(end, buffer.length);
+        uint256 sanitizedStart = Math.min(start, sanitizedEnd);
+        uint256 expectedLength = sanitizedEnd - sanitizedStart;
+
+        assertEq(result.length, expectedLength);
+
+        // Verify content matches when there's content to verify
+        for (uint256 i = 0; i < result.length; ++i) {
+            assertEq(result[i], buffer[sanitizedStart + i]);
+        }
+    }
+
+    function testSpliceWithStartOnly(bytes memory buffer, uint256 start) public pure {
+        bytes memory originalBuffer = bytes.concat(buffer);
+        bytes memory result = buffer.splice(start);
+
+        // Result should be the same object as input (modified in place)
+        assertEq(result, buffer);
+
+        // Should contain bytes from start to end, moved to beginning
+        assertEq(result.length, Math.saturatingSub(originalBuffer.length, start));
+
+        // Verify content matches moved content
+        for (uint256 i = 0; i < result.length; ++i) {
+            assertEq(result[i], originalBuffer[start + i]);
+        }
+    }
+
+    function testSplice(bytes memory buffer, uint256 start, uint256 end) public pure {
+        bytes memory originalBuffer = bytes.concat(buffer);
+        bytes memory result = buffer.splice(start, end);
+
+        // Result should be the same object as input (modified in place)
+        assertEq(result, buffer);
+
+        // Calculate expected bounds after sanitization
+        uint256 sanitizedEnd = Math.min(end, originalBuffer.length);
+        uint256 sanitizedStart = Math.min(start, sanitizedEnd);
+        uint256 expectedLength = sanitizedEnd - sanitizedStart;
+
+        assertEq(result.length, expectedLength);
+
+        // Verify content matches moved content
+        for (uint256 i = 0; i < result.length; ++i) {
+            assertEq(result[i], originalBuffer[sanitizedStart + i]);
+        }
+    }
+
     // REVERSE BITS
     function testSymbolicReverseBytes32(bytes32 value) public pure {
         assertEq(Bytes.reverseBytes32(Bytes.reverseBytes32(value)), value);

test/utils/Bytes.test.js

@@ -64,8 +64,8 @@ describe('Bytes', function () {
     });
   });
 
-  describe('slice', function () {
-    describe('slice(bytes, uint256)', function () {
+  describe('slice & splice', function () {
+    describe('slice(bytes, uint256) & splice(bytes, uint256)', function () {
       for (const [descr, start] of Object.entries({
         'start = 0': 0,
         'start within bound': 10,
@@ -74,11 +74,12 @@ 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);
         });
       }
     });
 
-    describe('slice(bytes, uint256, uint256)', function () {
+    describe('slice(bytes, uint256, uint256) & splice(bytes, uint256, uint256)', function () {
       for (const [descr, [start, end]] of Object.entries({
         'start = 0': [0, 42],
         'start and end within bound': [17, 42],
@@ -89,6 +90,7 @@ 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);
         });
       }
     });