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

@@ -130,11 +130,57 @@ 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);
+    }
+
+    /**
+     * @dev See {IERC1155-safeBatchTransferFrom}.
+     */
+    function safeBatchTransferFrom(
+        address from,
+        address to,
+        uint256[] memory ids,
+        uint256[] memory amounts,
+        bytes memory data
+    )
+        public
+        virtual
+        override
+    {
+        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();
 
@@ -151,25 +197,27 @@ contract ERC1155 is Context, ERC165, IERC1155, IERC1155MetadataURI {
     }
 
     /**
-     * @dev See {IERC1155-safeBatchTransferFrom}.
+     * @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(
+    function _safeBatchTransferFrom(
         address from,
         address to,
         uint256[] memory ids,
         uint256[] memory amounts,
         bytes memory data
     )
-        public
+        internal
         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"
-        );
 
         address operator = _msgSender();