Add immutable strings array library

packages/contracts/contracts/libs/v0.8.x/ImmutableStringArray.sol

@@ -0,0 +1,281 @@
+// SPDX-License-Identifier: LGPL-3.0-only
+// Created By: Art Blocks Inc.
+
+pragma solidity ^0.8.0;
+
+import {SSTORE2} from "./SSTORE2.sol"; // Import SSTORE2 library
+
+/**
+ * @title ImmutableStringArray
+ * @author Art Blocks Inc.
+ * @notice This library is optimized to store immutable arrays of strings much more efficiently than using native Solidity storage arrays.
+ * It uses a single SSTORE2 contract to store the length + packed offsets + packed string data.
+ * Allows overwriting the pointer to point to a new immutable array.
+ */
+library ImmutableStringArray {
+    /**
+     * @notice Struct to store the SSTORE2 pointer to the packed string array.
+     * @dev dataPointer is the SSTORE2 pointer to the packed string array.
+     */
+    struct StringArray {
+        address dataPointer; // SSTORE2 pointer storing length + packed offsets + packed string data
+    }
+
+    /**
+     * @notice Stores a packed immutable string array using a single SSTORE2 contract.
+     * Allows overwriting the pointer to point to a new immutable array.
+     * @param storageArray The storage reference to store the packed array.
+     * @param strings The array of strings to pack.
+     */
+    function store(
+        StringArray storage storageArray,
+        string[] memory strings
+    ) internal {
+        uint256 arrayLength = strings.length;
+        uint64[] memory offsets = new uint64[](arrayLength);
+
+        // compute total bytes length and offsets (ensuring no overflow)
+        uint256 totalStringBytesLength;
+        for (uint256 i = 0; i < arrayLength; i++) {
+            offsets[i] = uint64(totalStringBytesLength);
+            totalStringBytesLength += bytes(strings[i]).length;
+        }
+        // realistically will not overflow uint64, but check for security guarantees
+        // @dev no coverage on else (difficulty of triggering)
+        require(
+            totalStringBytesLength <= type(uint64).max,
+            "Offset exceeds uint64 limit"
+        );
+
+        // prepare the combined storage structure (length + packed offsets + packed strings)
+        // @dev 8 bytes for length, 8 bytes per offset, totalStringBytesLength bytes for strings
+        // over-allocate 32 bytes for memory safety
+        // note: shorten length by 32 bytes at end of function before returning
+        uint256 packedDataLength = 8 +
+            (arrayLength * 8) +
+            totalStringBytesLength;
+        bytes memory packedData = new bytes(packedDataLength + 0x20);
+        uint256 ptr;
+
+        // store the length of the strings array in the first 8 bytes of the packedData
+        assembly ("memory-safe") {
+            ptr := add(packedData, 0x20) // pointer to first byte of packedData
+            mstore(ptr, shl(192, arrayLength)) // left-align only 8 bytes in the 32-byte slot
+            ptr := add(ptr, 8) // move pointer forward by 8 bytes
+        }
+
+        // store offsets in packed `uint64` format
+        for (uint256 i = 0; i < arrayLength; i++) {
+            uint256 offset = offsets[i];
+            assembly ("memory-safe") {
+                mstore(ptr, shl(192, offset))
+                // move pointer ahead 8 bytes for uint64
+                ptr := add(ptr, 8)
+            }
+        }
+
+        // pack the strings efficiently, using assembly to copy 32 bytes at a time
+        for (uint i = 0; i < arrayLength; i++) {
+            bytes memory currentString = bytes(strings[i]);
+            uint currentLength = currentString.length;
+            uint currentPtr;
+
+            assembly ("memory-safe") {
+                currentPtr := add(currentString, 0x20) // start of current string's data
+            }
+
+            // copy the full 32-byte chunks
+            uint chunks = currentLength / 32;
+            uint remainder = currentLength % 32;
+            // store the full 32 byte chunks
+            for (uint j = 0; j < chunks; j++) {
+                assembly ("memory-safe") {
+                    let chunk := mload(currentPtr) // load 32 bytes of the current string
+                    mstore(ptr, chunk) // store the 32 bytes into the result
+                    ptr := add(ptr, 0x20) // move the result pointer forward by 32 bytes
+                    currentPtr := add(currentPtr, 0x20) // move the current string pointer forward by 32 bytes
+                }
+            }
+            // store any partial chunks
+            if (remainder > 0) {
+                bytes32 chunk;
+                assembly ("memory-safe") {
+                    chunk := mload(currentPtr) // load full 32-byte word
+                    // safe to write past end of final array - 32 bytes of buffer at end of array
+                    mstore(ptr, chunk) // store the final chunk's remaining bytes
+                    ptr := add(ptr, remainder) // move the result pointer forward by the remainder length for next iteration
+                }
+            }
+        }
+
+        // remove the buffer from the packedData bytes array length
+        assembly ("memory-safe") {
+            ptr := packedData
+            mstore(ptr, packedDataLength)
+        }
+
+        // Store all packed data in a SSTORE2 contract, store result in storage
+        storageArray.dataPointer = SSTORE2.write(packedData);
+    }
+
+    /**
+     * @notice Retrieves the total number of stored strings from SSTORE2.
+     * @param storageArray The storage reference containing packed strings.
+     * @return count The count of stored strings.
+     */
+    function length(
+        StringArray storage storageArray
+    ) internal view returns (uint256 count) {
+        // @dev this could be more efficient by only reading the first 8 bytes of the SSTORE2 contract
+        // but prefer to keep simple
+        bytes memory allData = SSTORE2.read(storageArray.dataPointer);
+
+        assembly ("memory-safe") {
+            count := shr(192, mload(add(allData, 32)))
+        }
+    }
+
+    /**
+     * @notice Retrieves a single string from storage by index.
+     * @param storageArray The storage reference containing packed strings.
+     * @param index The index of the string to retrieve.
+     * @return result The retrieved string.
+     */
+    function get(
+        StringArray storage storageArray,
+        uint256 index
+    ) internal view returns (string memory result) {
+        bytes memory allData = SSTORE2.read(storageArray.dataPointer);
+        uint256 offsetsStart;
+        uint64 start;
+        uint64 end;
+        // load the total length of the strings array from the first 8 bytes of the SSTORE2 contract
+        uint256 arrayLength;
+        assembly ("memory-safe") {
+            arrayLength := shr(192, mload(add(allData, 32)))
+        }
+
+        require(index < arrayLength, "Index out of bounds");
+        if (index + 1 == arrayLength) {
+            uint256 allDataLength = allData.length;
+            assembly ("memory-safe") {
+                offsetsStart := add(allData, 40) // skipping first 8 bytes (length)
+                start := shr(192, mload(add(offsetsStart, mul(index, 8)))) // load offsets[index] as uint64
+                end := sub(
+                    allDataLength,
+                    add(8, mul(arrayLength, 8)) // subtract 8 bytes for overall array length, and 8*length for the offsets section
+                )
+            }
+        } else {
+            assembly ("memory-safe") {
+                offsetsStart := add(allData, 40) // skipping first 8 bytes (length)
+                start := shr(192, mload(add(offsetsStart, mul(index, 8)))) // load offsets[index] as uint64
+                end := shr(192, mload(add(offsetsStart, mul(add(index, 1), 8)))) // load offsets[index + 1]
+            }
+        }
+
+        uint256 strLength = end - start;
+        // over-allocate 32 bytes for memory safety
+        bytes memory strBytes = new bytes(strLength + 32);
+        uint256 ptr;
+        assembly ("memory-safe") {
+            ptr := add(strBytes, 0x20) // pointer to first byte of strBytes
+        }
+
+        // efficiently copy 32 bytes at a time from allData to strBytes
+        for (uint256 i = 0; i < strLength; i += 32) {
+            // offset = 32 bytes for length + 8 bytes for overall array length + 8 bytes per offset * length of array + start of string + i
+            uint256 offset = 32 + 8 + (arrayLength * 8) + start + i;
+            assembly ("memory-safe") {
+                let chunk := mload(add(allData, offset)) // load 32 bytes of the current string
+                mstore(ptr, chunk) // store the 32 bytes into the result (buffer keeps this memory safe)
+                ptr := add(ptr, 0x20) // move the result pointer forward by 32 bytes
+            }
+        }
+
+        // remove the buffer length from the strBytes bytes array length
+        assembly ("memory-safe") {
+            ptr := strBytes
+            mstore(ptr, strLength)
+        }
+        result = string(strBytes);
+    }
+
+    /**
+     * @notice Retrieves all stored strings in a single batch call.
+     * @param storageArray The storage reference containing packed strings.
+     * @return results An array of all stored strings.
+     */
+    function getAll(
+        StringArray storage storageArray
+    ) internal view returns (string[] memory results) {
+        // load the packed data from the SSTORE2 contract
+        bytes memory allData = SSTORE2.read(storageArray.dataPointer);
+        // load the total length of the strings array from the first 8 bytes of the SSTORE2 contract
+        uint256 arrayLength;
+        assembly ("memory-safe") {
+            arrayLength := shr(192, mload(add(allData, 32)))
+        }
+
+        // for each string in the array, populate results
+        results = new string[](arrayLength);
+
+        for (uint256 index = 0; index < arrayLength; index++) {
+            // @dev start and end are calculated for each index for code simplicity/code re-use from get() function
+            uint256 offsetsStart;
+            uint64 start;
+            uint64 end;
+
+            if (index + 1 == arrayLength) {
+                uint256 allDataLength = allData.length;
+                assembly ("memory-safe") {
+                    offsetsStart := add(allData, 40) // Skipping first 8 bytes (length)
+                    start := shr(192, mload(add(offsetsStart, mul(index, 8)))) // Load offsets[index] as uint64
+                    end := sub(
+                        allDataLength,
+                        add(8, mul(arrayLength, 8)) // subtract 8 bytes for overall array length, and 8*length for the offsets section
+                    )
+                }
+            } else {
+                assembly ("memory-safe") {
+                    offsetsStart := add(allData, 40) // Skipping first 8 bytes (length)
+                    start := shr(192, mload(add(offsetsStart, mul(index, 8)))) // Load offsets[index] as uint64
+                    end := shr(
+                        192,
+                        mload(add(offsetsStart, mul(add(index, 1), 8)))
+                    ) // Load offsets[index + 1]
+                }
+            }
+
+            uint256 strLength = end - start;
+            // over-allocate 32 bytes for memory safety
+            bytes memory strBytes = new bytes(strLength + 32);
+            uint256 ptr;
+            assembly ("memory-safe") {
+                ptr := add(strBytes, 0x20) // pointer to first byte of strBytes
+            }
+
+            // efficiently copy 32 bytes at a time from allData to strBytes
+            for (uint256 i = 0; i < strLength; i += 32) {
+                // offset = 32 bytes for length + 8 bytes for overall array length + 8 bytes per offset * length of array + start of string + i
+                uint256 offset = 32 + 8 + (arrayLength * 8) + start + i;
+                assembly ("memory-safe") {
+                    let chunk := mload(add(allData, offset)) // Load 32 bytes of the current string
+                    mstore(ptr, chunk) // Store the 32 bytes into the result (buffer keeps this memory safe)
+                    ptr := add(ptr, 0x20) // Move the result pointer forward by 32 bytes
+                }
+            }
+
+            // remove the buffer length from the strBytes bytes array length
+            assembly ("memory-safe") {
+                ptr := strBytes
+                mstore(ptr, strLength)
+            }
+
+            // store the string in the results array
+            results[index] = string(strBytes);
+        }
+
+        // results is returned by reference, so no need for explicit return
+    }
+}

packages/contracts/contracts/mock/ImmutableStringArrayMock.sol

@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+import {ImmutableStringArray} from "../libs/v0.8.x/ImmutableStringArray.sol";
+
+/**
+ * @title ImmutableStringArrayMock
+ * @notice Mock contract for testing ImmutableStringArray library functionality
+ */
+contract ImmutableStringArrayMock {
+    using ImmutableStringArray for ImmutableStringArray.StringArray;
+
+    ImmutableStringArray.StringArray private stringArray;
+
+    /**
+     * @notice Store an array of strings
+     * @param strings The array of strings to store
+     */
+    function store(string[] memory strings) external {
+        stringArray.store(strings);
+    }
+
+    /**
+     * @notice Get the length of the stored array
+     * @return The number of strings stored
+     */
+    function length() external view returns (uint256) {
+        return stringArray.length();
+    }
+
+    /**
+     * @notice Get a string at a specific index
+     * @param index The index to retrieve
+     * @return The string at the given index
+     */
+    function get(uint256 index) external view returns (string memory) {
+        return stringArray.get(index);
+    }
+
+    /**
+     * @notice Get all stored strings
+     * @return An array containing all stored strings
+     */
+    function getAll() external view returns (string[] memory) {
+        return stringArray.getAll();
+    }
+}