Refactor ERC1155 transfers to use internal functions (#2636)

* Refactor ERC1155 transfers to use internal functions #2622

* apply length check to all internal calls

Co-authored-by: Robert Kaiser <kairo@kairo.at>

contracts/token/ERC1155/ERC1155.sol

@@ -130,24 +130,11 @@ contract ERC1155 is Context, ERC165, IERC1155, IERC1155MetadataURI {
         virtual
         override
     {
-        require(to != address(0), "ERC1155: transfer to the zero address");
         require(
             from == _msgSender() || isApprovedForAll(from, _msgSender()),
             "ERC1155: caller is not owner nor approved"
         );
-
+        _safeTransferFrom(from, to, id, amount, data);
-        address operator = _msgSender();
-
-        _beforeTokenTransfer(operator, from, to, _asSingletonArray(id), _asSingletonArray(amount), data);
-
-        uint256 fromBalance = _balances[id][from];
-        require(fromBalance >= amount, "ERC1155: insufficient balance for transfer");
-        _balances[id][from] = fromBalance - amount;
-        _balances[id][to] += amount;
-
-        emit TransferSingle(operator, from, to, id, amount);
-
-        _doSafeTransferAcceptanceCheck(operator, from, to, id, amount, data);
     }
 
     /**
@@ -164,12 +151,73 @@ contract ERC1155 is Context, ERC165, IERC1155, IERC1155MetadataURI {
         virtual
         override
     {
-        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");
-        require(to != address(0), "ERC1155: transfer to the zero address");
         require(
             from == _msgSender() || isApprovedForAll(from, _msgSender()),
             "ERC1155: transfer caller is not owner nor approved"
         );
+        _safeBatchTransferFrom(from, to, ids, amounts, data);
+    }
+
+    /**
+     * @dev Transfers `amount` tokens of token type `id` from `from` to `to`.
+     *
+     * Emits a {TransferSingle} event.
+     *
+     * Requirements:
+     *
+     * - `to` cannot be the zero address.
+     * - `from` must have a balance of tokens of type `id` of at least `amount`.
+     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155Received} and return the
+     * acceptance magic value.
+     */
+    function _safeTransferFrom(
+        address from,
+        address to,
+        uint256 id,
+        uint256 amount,
+        bytes memory data
+    )
+        internal
+        virtual
+    {
+        require(to != address(0), "ERC1155: transfer to the zero address");
+
+        address operator = _msgSender();
+
+        _beforeTokenTransfer(operator, from, to, _asSingletonArray(id), _asSingletonArray(amount), data);
+
+        uint256 fromBalance = _balances[id][from];
+        require(fromBalance >= amount, "ERC1155: insufficient balance for transfer");
+        _balances[id][from] = fromBalance - amount;
+        _balances[id][to] += amount;
+
+        emit TransferSingle(operator, from, to, id, amount);
+
+        _doSafeTransferAcceptanceCheck(operator, from, to, id, amount, data);
+    }
+
+    /**
+     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {_safeTransferFrom}.
+     *
+     * Emits a {TransferBatch} event.
+     *
+     * Requirements:
+     *
+     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155BatchReceived} and return the
+     * acceptance magic value.
+     */
+    function _safeBatchTransferFrom(
+        address from,
+        address to,
+        uint256[] memory ids,
+        uint256[] memory amounts,
+        bytes memory data
+    )
+        internal
+        virtual
+    {
+        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");
+        require(to != address(0), "ERC1155: transfer to the zero address");
 
         address operator = _msgSender();