From 12ce4afe35cf4d75664615e80effb8208b41c86c Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 15:44:18 +0530
Subject: [PATCH 01/16] new: batch deposit of ERC721 tokens in mintable
 predicate

---
 .../MintableERC721Predicate.sol               | 51 +++++++++++++++++--
 1 file changed, 46 insertions(+), 5 deletions(-)

diff --git a/contracts/root/TokenPredicates/MintableERC721Predicate.sol b/contracts/root/TokenPredicates/MintableERC721Predicate.sol
index f373da73..b5c49af0 100644
--- a/contracts/root/TokenPredicates/MintableERC721Predicate.sol
+++ b/contracts/root/TokenPredicates/MintableERC721Predicate.sol
@@ -27,6 +27,13 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
         uint256 tokenId
     );
 
+    event LockedMintableERC721Batch(
+        address indexed depositor,
+        address indexed depositReceiver,
+        address indexed rootToken,
+        uint256[] tokenIds
+    );
+
     constructor() public {}
 
     function initialize(address _owner) external initializer {
@@ -52,11 +59,11 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
     }
 
     /**
-     * @notice Lock ERC721 tokens for deposit, callable only by manager
+     * @notice Lock ERC721 token(s) for deposit, callable only by manager
      * @param depositor Address who wants to deposit token
      * @param depositReceiver Address (address) who wants to receive token on child chain
      * @param rootToken Token which gets deposited
-     * @param depositData ABI encoded tokenId
+     * @param depositData ABI encoded tokenId(s). It's possible to deposit batch of tokens.
      */
     function lockTokens(
         address depositor,
@@ -68,9 +75,43 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
         override
         only(MANAGER_ROLE)
     {
-        uint256 tokenId = abi.decode(depositData, (uint256));
-        emit LockedMintableERC721(depositor, depositReceiver, rootToken, tokenId);
-        IMintableERC721(rootToken).safeTransferFrom(depositor, address(this), tokenId);
+
+        // Locking single ERC721 token
+        if (depositData.length == 32) {
+
+            uint256 tokenId = abi.decode(depositData, (uint256));
+
+            // Emitting event that single token is getting locked in predicate
+            emit LockedMintableERC721(depositor, depositReceiver, rootToken, tokenId);
+
+            // Transferring token to this address, which will be
+            // released when attempted to be unlocked
+            IERC721(rootToken).safeTransferFrom(depositor, address(this), tokenId);
+
+        } else {
+            // Locking a set a ERC721 token(s)
+
+            uint256[] memory tokenIds = abi.decode(depositData, (uint256[]));
+
+            // Emitting event that a set of ERC721 tokens are getting lockec
+            // in this predicate contract
+            emit LockedMintableERC721Batch(depositor, depositReceiver, rootToken, tokenIds);
+
+            // These many tokens are attempted to be deposited
+            // by user
+            uint256 length = tokenIds.length;
+            require(length <= BATCH_LIMIT, "MintableERC721Predicate: EXCEEDS_BATCH_LIMIT");
+
+            // Iteratively trying to transfer ERC721 token
+            // to this predicate address
+            for (uint256 i; i < length; i++) {
+
+                IERC721(rootToken).safeTransferFrom(depositor, address(this), tokenIds[i]);
+
+            }
+
+        }
+
     }
 
     /**

From 7887b7bbffd0197a3c1871d7ccd65d351312cafa Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 16:12:20 +0530
Subject: [PATCH 02/16] new: batch withdraw in mintable ERC721 predicate

---
 .../MintableERC721Predicate.sol               | 28 +++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/contracts/root/TokenPredicates/MintableERC721Predicate.sol b/contracts/root/TokenPredicates/MintableERC721Predicate.sol
index b5c49af0..21cf5ab3 100644
--- a/contracts/root/TokenPredicates/MintableERC721Predicate.sol
+++ b/contracts/root/TokenPredicates/MintableERC721Predicate.sol
@@ -15,9 +15,11 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
     bytes32 public constant MANAGER_ROLE = 0x241ecf16d79d0f8dbfb92cbc07fe17840425976cf0667f022fe9877caa831b08;
     // keccak256("MintableERC721")
     bytes32 public constant TOKEN_TYPE = 0xd4392723c111fcb98b073fe55873efb447bcd23cd3e49ec9ea2581930cd01ddc;
-    // keccak("Transfer(address,address,uint256)")
+    // keccak256("Transfer(address,address,uint256)")
     bytes32 public constant TRANSFER_EVENT_SIG = 0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef;
-    // keccak("TransferWithMetadata(address,address,uint256,string)")
+    // keccak256("WithdrawnBatch(address,uint256[])")
+    bytes32 public constant WITHDRAW_BATCH_EVENT_SIG = 0xf871896b17e9cb7a64941c62c188a4f5c621b86800e3d15452ece01ce56073df;
+    // keccak256("TransferWithMetadata(address,address,uint256,string)")
     bytes32 public constant TRANSFER_WITH_METADATA_EVENT_SIG = 0xf3c6803764de9a0fc1c2acb6a71f53407c5e2b9a3e04973e6586da23d64ecaa5;
 
     event LockedMintableERC721(
@@ -158,6 +160,28 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
                 token.mint(withdrawer, tokenId);
             }
 
+        } else if (bytes32(logTopicRLPList[0].toUint()) == WITHDRAW_BATCH_EVENT_SIG) { // topic0 is event sig
+            // If it's a simple batch exit, where a set of
+            // ERC721s were burnt in child chain with event signature
+            // looking like `WithdrawnBatch(address indexed user, uint256[] tokenIds);`
+            //
+            // @note This doesn't allow transfer of metadata cross chain
+            // For that check below `else if` block
+
+            address withdrawer = address(logTopicRLPList[1].toUint()); // topic1 is from address
+
+            // RLP encoded tokenId list
+            bytes memory logData = logRLPList[2].toBytes();
+
+            (uint256[] memory tokenIds) = abi.decode(logData, (uint256[]));
+            uint256 length = tokenIds.length;
+
+            for (uint256 i; i < length; i++) {
+
+                IERC721(rootToken).safeTransferFrom(address(this), withdrawer, tokenIds[i]);
+
+            }
+
         } else if (bytes32(logTopicRLPList[0].toUint()) == TRANSFER_WITH_METADATA_EVENT_SIG) { 
             // If this is NFT exit with metadata i.e. URI 👆
             //

From 3b79ef6060e6bf03b135e9de5c11817b5c2da81f Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 16:21:32 +0530
Subject: [PATCH 03/16] new: batch deposit/ withdraw in child mintable ERC721
 implementation

---
 .../child/ChildToken/ChildMintableERC721.sol  | 61 +++++++++++++++++--
 1 file changed, 56 insertions(+), 5 deletions(-)

diff --git a/contracts/child/ChildToken/ChildMintableERC721.sol b/contracts/child/ChildToken/ChildMintableERC721.sol
index 1572fec8..a5f4e742 100644
--- a/contracts/child/ChildToken/ChildMintableERC721.sol
+++ b/contracts/child/ChildToken/ChildMintableERC721.sol
@@ -19,6 +19,14 @@ contract ChildMintableERC721 is
 
     event TransferWithMetadata(address indexed from, address indexed to, uint256 indexed tokenId, bytes metaData);
 
+    // limit batching of tokens due to gas limit restrictions
+    uint256 public constant BATCH_LIMIT = 20;
+
+    event WithdrawnBatch(
+        address indexed user,
+        uint256[] tokenIds
+    );
+
     constructor(
         string memory name_,
         string memory symbol_,
@@ -44,20 +52,34 @@ contract ChildMintableERC721 is
     /**
      * @notice called when token is deposited on root chain
      * @dev Should be callable only by ChildChainManager
-     * Should handle deposit by minting the required tokenId for user
+     * Should handle deposit by minting the required tokenId(s) for user
      * Should set `withdrawnTokens` mapping to `false` for the tokenId being deposited
      * Minting can also be done by other functions
      * @param user user address for whom deposit is being done
-     * @param depositData abi encoded tokenId
+     * @param depositData abi encoded tokenIds. Batch deposit also supported.
      */
     function deposit(address user, bytes calldata depositData)
         external
         override
         only(DEPOSITOR_ROLE)
     {
-        uint256 tokenId = abi.decode(depositData, (uint256));
-        withdrawnTokens[tokenId] = false;
-        _mint(user, tokenId);
+
+        // deposit single
+        if (depositData.length == 32) {
+            uint256 tokenId = abi.decode(depositData, (uint256));
+            withdrawnTokens[tokenId] = false;
+            _mint(user, tokenId);
+
+        // deposit batch
+        } else {
+            uint256[] memory tokenIds = abi.decode(depositData, (uint256[]));
+            uint256 length = tokenIds.length;
+            for (uint256 i; i < length; i++) {
+                withdrawnTokens[tokenIds[i]] = false;
+                _mint(user, tokenIds[i]);
+            }
+        }
+
     }
 
     /**
@@ -73,6 +95,35 @@ contract ChildMintableERC721 is
         _burn(tokenId);
     }
 
+    /**
+     * @notice called when user wants to withdraw multiple tokens back to root chain
+     * @dev Should burn user's tokens. This transaction will be verified when exiting on root chain
+     * @param tokenIds tokenId list to withdraw
+     */
+    function withdrawBatch(uint256[] calldata tokenIds) external {
+
+        uint256 length = tokenIds.length;
+        require(length <= BATCH_LIMIT, "ChildMintableERC721: EXCEEDS_BATCH_LIMIT");
+
+        // Iteratively burn ERC721 tokens, for performing
+        // batch withdraw
+        for (uint256 i; i < length; i++) {
+
+            uint256 tokenId = tokenIds[i];
+
+            require(_msgSender() == ownerOf(tokenId), string(abi.encodePacked("ChildMintableERC721: INVALID_TOKEN_OWNER ", tokenId)));
+            withdrawnTokens[tokenId] = true;
+            _burn(tokenId);
+
+        }
+
+        // At last emit this event, which will be used
+        // in MintableERC721 predicate contract on L1
+        // while verifying burn proof
+        emit WithdrawnBatch(_msgSender(), tokenIds);
+
+    }
+
     /**
      * @notice called when user wants to withdraw token back to root chain with token URI
      * @dev Should handle withraw by burning user's token.

From dff39a0b513bbb15efa6a2e0922a49f093dfe487 Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 16:46:17 +0530
Subject: [PATCH 04/16] new: withdraw a batch of tokens with respective
 metadata, for child token

---
 .../child/ChildToken/ChildMintableERC721.sol  | 58 ++++++++++++++++---
 1 file changed, 49 insertions(+), 9 deletions(-)

diff --git a/contracts/child/ChildToken/ChildMintableERC721.sol b/contracts/child/ChildToken/ChildMintableERC721.sol
index a5f4e742..3edf92a8 100644
--- a/contracts/child/ChildToken/ChildMintableERC721.sol
+++ b/contracts/child/ChildToken/ChildMintableERC721.sol
@@ -17,15 +17,12 @@ contract ChildMintableERC721 is
     bytes32 public constant DEPOSITOR_ROLE = keccak256("DEPOSITOR_ROLE");
     mapping (uint256 => bool) public withdrawnTokens;
 
-    event TransferWithMetadata(address indexed from, address indexed to, uint256 indexed tokenId, bytes metaData);
-
     // limit batching of tokens due to gas limit restrictions
     uint256 public constant BATCH_LIMIT = 20;
 
-    event WithdrawnBatch(
-        address indexed user,
-        uint256[] tokenIds
-    );
+    event WithdrawnBatch(address indexed user, uint256[] tokenIds);
+    event TransferWithMetadata(address indexed from, address indexed to, uint256 indexed tokenId, bytes metaData);
+    event WithdrawBatchWithMetadata(address indexed from, address indexed to, uint256[] tokenIds, bytes[] metaData);
 
     constructor(
         string memory name_,
@@ -130,9 +127,6 @@ contract ChildMintableERC721 is
      * Should set `withdrawnTokens` mapping to `true` for the tokenId being withdrawn
      * This transaction will be verified when exiting on root chain
      *
-     * Before calling this function, you may want calling `encodeTokenMetadata`
-     * and get metadata to be transferred from L2 to L1 during exit
-     *
      * @param tokenId tokenId to withdraw
      */
     function withdrawWithMetadata(uint256 tokenId) external {
@@ -147,6 +141,52 @@ contract ChildMintableERC721 is
 
     }
 
+    /**
+     * @notice called when user wants to withdraw tokens i.e. a batch of tokens, back to root chain with all respective metaData
+     * @dev Should handle withraw by burning user's token.
+     * Should set `withdrawnTokens` mapping to `true` for the tokenId being withdrawn
+     * This transaction will be verified when exiting on root chain
+     *
+     * @param tokenId tokenId to withdraw
+     */
+    function withdrawBatchWithMetadata(uint256 calldata tokenIds) external {
+
+        uint256 length = tokenIds.length;
+        require(length <= BATCH_LIMIT, "ChildMintableERC721: EXCEEDS_BATCH_LIMIT");
+
+        // During iteratively burning tokens, attempting
+        // to store respective metadata
+        //
+        // To be emitted with event, which will be
+        // verified on L1 & used for setting token metadata
+        // when exiting from L2 to L1
+        uint256[length] memory metaData;
+
+        // Iteratively burn ERC721 tokens, for performing
+        // batch withdraw
+        for (uint256 i; i < length; i++) {
+
+            uint256 tokenId = tokenIds[i];
+
+            require(_msgSender() == ownerOf(tokenId), string(abi.encodePacked("ChildMintableERC721: INVALID_TOKEN_OWNER ", tokenId)));
+            // Marking token has been withdrawn
+            withdrawnTokens[tokenId] = true;
+
+            // Storing metadata of respective token
+            // in ordered fashion
+            metaData[i] = this.encodeTokenMetadata(tokenId);
+            // Then burning token
+            _burn(tokenId);
+
+        }
+
+        // At last emit this event, which will be used
+        // in MintableERC721 predicate contract on L1
+        // while verifying burn proof
+        emit WithdrawBatchWithMetadata(_msgSender(), address(0), tokenIds, metaData);
+
+    }
+
     /**
      * @notice This method is supposed to be called by client when withdrawing token with metadata
      * and pass return value of this function as second paramter of `withdrawWithMetadata` method

From 824caf0b526e4324d48ae593df1e71b38539ff34 Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 18:33:27 +0530
Subject: [PATCH 05/16] new: batch withdraw op for mintable ERC721

---
 .../MintableERC721Predicate.sol               | 76 ++++++++++++++++++-
 1 file changed, 73 insertions(+), 3 deletions(-)

diff --git a/contracts/root/TokenPredicates/MintableERC721Predicate.sol b/contracts/root/TokenPredicates/MintableERC721Predicate.sol
index 21cf5ab3..46514743 100644
--- a/contracts/root/TokenPredicates/MintableERC721Predicate.sol
+++ b/contracts/root/TokenPredicates/MintableERC721Predicate.sol
@@ -19,8 +19,10 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
     bytes32 public constant TRANSFER_EVENT_SIG = 0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef;
     // keccak256("WithdrawnBatch(address,uint256[])")
     bytes32 public constant WITHDRAW_BATCH_EVENT_SIG = 0xf871896b17e9cb7a64941c62c188a4f5c621b86800e3d15452ece01ce56073df;
-    // keccak256("TransferWithMetadata(address,address,uint256,string)")
-    bytes32 public constant TRANSFER_WITH_METADATA_EVENT_SIG = 0xf3c6803764de9a0fc1c2acb6a71f53407c5e2b9a3e04973e6586da23d64ecaa5;
+    // keccak256("TransferWithMetadata(address,address,uint256,bytes)")
+    bytes32 public constant TRANSFER_WITH_METADATA_EVENT_SIG = 0xf94915c6d1fd521cee85359239227480c7e8776d7caf1fc3bacad5c269b66a14;
+    // keccak256("WithdrawBatchWithMetadata(address,address,uint256[],bytes[])")
+    bytes32 public constant WITHDRAW_BATCH_WITH_METADATA_EVENT_SIG = 0x4f83879b5380fb2113c27cb03563cd911fe5f79f11b4ce5c470b40070c2acd86;
 
     event LockedMintableERC721(
         address indexed depositor,
@@ -176,9 +178,27 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
             (uint256[] memory tokenIds) = abi.decode(logData, (uint256[]));
             uint256 length = tokenIds.length;
 
+            IMintableERC721 token = IMintableERC721(rootToken);
+
             for (uint256 i; i < length; i++) {
 
-                IERC721(rootToken).safeTransferFrom(address(this), withdrawer, tokenIds[i]);
+                uint256 tokenId = tokenIds[i];
+
+                // Check if token exists or not
+                //
+                // If does, transfer token to withdrawer
+                if (token.exists(tokenId)) {
+                    token.safeTransferFrom(
+                        address(this),
+                        withdrawer,
+                        tokenId
+                    );
+                } else {
+                    // If token was minted on L2
+                    // we'll mint it here, on L1, during
+                    // exiting from L2
+                    token.mint(withdrawer, tokenId);
+                }
 
             }
 
@@ -217,6 +237,56 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
                 token.mint(withdrawer, tokenId, logRLPList[2].toBytes());
             }
 
+        } else if (bytes32(logTopicRLPList[0].toUint()) == WITHDRAW_BATCH_WITH_METADATA_EVENT_SIG) {
+            // If this is batch NFT exit with all respective metadata 👆
+            //
+            // Note: This is nothing but batch version of previous
+            // block of code
+
+            address withdrawer = address(logTopicRLPList[1].toUint()); // topic1 is from address
+
+            require(
+                address(logTopicRLPList[2].toUint()) == address(0), // topic2 is to address
+                "MintableERC721Predicate: INVALID_RECEIVER"
+            );
+
+            IMintableERC721 token = IMintableERC721(rootToken);
+
+            // RLP encoded tokenId, token metadata list ( in ordered form )
+            bytes memory logData = logRLPList[2].toBytes();
+
+            (uint256[] memory tokenIds, bytes[] memory metaData) = abi.decode(logData, (uint256[], bytes[]));
+            require(tokenIds.length == metaData.length, "MintableERC721Predicate: TokenId & Metadata Length Mismatch");
+
+            uint256 length = tokenIds.length;
+
+            for (uint256 i; i < length; i++) {
+
+                uint256 tokenId = tokenIds[i];
+
+                // Check if token exists or not
+                //
+                // If does, transfer token to withdrawer
+                if (token.exists(tokenId)) {
+
+                    token.safeTransferFrom(
+                        address(this),
+                        withdrawer,
+                        tokenId
+                    );
+
+                } else {
+
+                    // If token was minted on L2
+                    // we'll mint it here, on L1, during
+                    // exiting from L2, while setting its
+                    // metadata passed from L2
+                    token.mint(withdrawer, tokenId, metadata[i]);
+
+                }
+
+            }
+
         } else {
             // Attempting to exit with some event signature from L2, which is
             // not ( yet ) supported by L1 exit manager

From 1376ec4011399d9ba6e2696dc19c499e1a7429e0 Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 18:49:54 +0530
Subject: [PATCH 06/16] chg: removed batch withdraw with metadata

---
 .../child/ChildToken/ChildMintableERC721.sol  | 47 ---------------
 .../MintableERC721Predicate.sol               | 59 ++-----------------
 2 files changed, 5 insertions(+), 101 deletions(-)

diff --git a/contracts/child/ChildToken/ChildMintableERC721.sol b/contracts/child/ChildToken/ChildMintableERC721.sol
index 3edf92a8..2a10191a 100644
--- a/contracts/child/ChildToken/ChildMintableERC721.sol
+++ b/contracts/child/ChildToken/ChildMintableERC721.sol
@@ -22,7 +22,6 @@ contract ChildMintableERC721 is
 
     event WithdrawnBatch(address indexed user, uint256[] tokenIds);
     event TransferWithMetadata(address indexed from, address indexed to, uint256 indexed tokenId, bytes metaData);
-    event WithdrawBatchWithMetadata(address indexed from, address indexed to, uint256[] tokenIds, bytes[] metaData);
 
     constructor(
         string memory name_,
@@ -141,52 +140,6 @@ contract ChildMintableERC721 is
 
     }
 
-    /**
-     * @notice called when user wants to withdraw tokens i.e. a batch of tokens, back to root chain with all respective metaData
-     * @dev Should handle withraw by burning user's token.
-     * Should set `withdrawnTokens` mapping to `true` for the tokenId being withdrawn
-     * This transaction will be verified when exiting on root chain
-     *
-     * @param tokenId tokenId to withdraw
-     */
-    function withdrawBatchWithMetadata(uint256 calldata tokenIds) external {
-
-        uint256 length = tokenIds.length;
-        require(length <= BATCH_LIMIT, "ChildMintableERC721: EXCEEDS_BATCH_LIMIT");
-
-        // During iteratively burning tokens, attempting
-        // to store respective metadata
-        //
-        // To be emitted with event, which will be
-        // verified on L1 & used for setting token metadata
-        // when exiting from L2 to L1
-        uint256[length] memory metaData;
-
-        // Iteratively burn ERC721 tokens, for performing
-        // batch withdraw
-        for (uint256 i; i < length; i++) {
-
-            uint256 tokenId = tokenIds[i];
-
-            require(_msgSender() == ownerOf(tokenId), string(abi.encodePacked("ChildMintableERC721: INVALID_TOKEN_OWNER ", tokenId)));
-            // Marking token has been withdrawn
-            withdrawnTokens[tokenId] = true;
-
-            // Storing metadata of respective token
-            // in ordered fashion
-            metaData[i] = this.encodeTokenMetadata(tokenId);
-            // Then burning token
-            _burn(tokenId);
-
-        }
-
-        // At last emit this event, which will be used
-        // in MintableERC721 predicate contract on L1
-        // while verifying burn proof
-        emit WithdrawBatchWithMetadata(_msgSender(), address(0), tokenIds, metaData);
-
-    }
-
     /**
      * @notice This method is supposed to be called by client when withdrawing token with metadata
      * and pass return value of this function as second paramter of `withdrawWithMetadata` method
diff --git a/contracts/root/TokenPredicates/MintableERC721Predicate.sol b/contracts/root/TokenPredicates/MintableERC721Predicate.sol
index 46514743..453cf406 100644
--- a/contracts/root/TokenPredicates/MintableERC721Predicate.sol
+++ b/contracts/root/TokenPredicates/MintableERC721Predicate.sol
@@ -21,8 +21,9 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
     bytes32 public constant WITHDRAW_BATCH_EVENT_SIG = 0xf871896b17e9cb7a64941c62c188a4f5c621b86800e3d15452ece01ce56073df;
     // keccak256("TransferWithMetadata(address,address,uint256,bytes)")
     bytes32 public constant TRANSFER_WITH_METADATA_EVENT_SIG = 0xf94915c6d1fd521cee85359239227480c7e8776d7caf1fc3bacad5c269b66a14;
-    // keccak256("WithdrawBatchWithMetadata(address,address,uint256[],bytes[])")
-    bytes32 public constant WITHDRAW_BATCH_WITH_METADATA_EVENT_SIG = 0x4f83879b5380fb2113c27cb03563cd911fe5f79f11b4ce5c470b40070c2acd86;
+
+    // limit batching of tokens due to gas limit restrictions
+    uint256 public constant BATCH_LIMIT = 20;
 
     event LockedMintableERC721(
         address indexed depositor,
@@ -90,7 +91,7 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
 
             // Transferring token to this address, which will be
             // released when attempted to be unlocked
-            IERC721(rootToken).safeTransferFrom(depositor, address(this), tokenId);
+            IMintableERC721(rootToken).safeTransferFrom(depositor, address(this), tokenId);
 
         } else {
             // Locking a set a ERC721 token(s)
@@ -110,7 +111,7 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
             // to this predicate address
             for (uint256 i; i < length; i++) {
 
-                IERC721(rootToken).safeTransferFrom(depositor, address(this), tokenIds[i]);
+                IMintableERC721(rootToken).safeTransferFrom(depositor, address(this), tokenIds[i]);
 
             }
 
@@ -237,56 +238,6 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
                 token.mint(withdrawer, tokenId, logRLPList[2].toBytes());
             }
 
-        } else if (bytes32(logTopicRLPList[0].toUint()) == WITHDRAW_BATCH_WITH_METADATA_EVENT_SIG) {
-            // If this is batch NFT exit with all respective metadata 👆
-            //
-            // Note: This is nothing but batch version of previous
-            // block of code
-
-            address withdrawer = address(logTopicRLPList[1].toUint()); // topic1 is from address
-
-            require(
-                address(logTopicRLPList[2].toUint()) == address(0), // topic2 is to address
-                "MintableERC721Predicate: INVALID_RECEIVER"
-            );
-
-            IMintableERC721 token = IMintableERC721(rootToken);
-
-            // RLP encoded tokenId, token metadata list ( in ordered form )
-            bytes memory logData = logRLPList[2].toBytes();
-
-            (uint256[] memory tokenIds, bytes[] memory metaData) = abi.decode(logData, (uint256[], bytes[]));
-            require(tokenIds.length == metaData.length, "MintableERC721Predicate: TokenId & Metadata Length Mismatch");
-
-            uint256 length = tokenIds.length;
-
-            for (uint256 i; i < length; i++) {
-
-                uint256 tokenId = tokenIds[i];
-
-                // Check if token exists or not
-                //
-                // If does, transfer token to withdrawer
-                if (token.exists(tokenId)) {
-
-                    token.safeTransferFrom(
-                        address(this),
-                        withdrawer,
-                        tokenId
-                    );
-
-                } else {
-
-                    // If token was minted on L2
-                    // we'll mint it here, on L1, during
-                    // exiting from L2, while setting its
-                    // metadata passed from L2
-                    token.mint(withdrawer, tokenId, metadata[i]);
-
-                }
-
-            }
-
         } else {
             // Attempting to exit with some event signature from L2, which is
             // not ( yet ) supported by L1 exit manager

From 42415b08876e7c2ba8e3afd630c7056967318cf0 Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 18:50:17 +0530
Subject: [PATCH 07/16] gen: flattened contracts

---
 flat/BaseRootTunnel.sol          |   1 -
 flat/ChildMintableERC721.sol     |  60 +++++++++++++++---
 flat/MintableERC721Predicate.sol | 102 ++++++++++++++++++++++++++++---
 flat/RootTunnel.sol              |   1 -
 4 files changed, 146 insertions(+), 18 deletions(-)

diff --git a/flat/BaseRootTunnel.sol b/flat/BaseRootTunnel.sol
index 95ee91de..ace6a494 100644
--- a/flat/BaseRootTunnel.sol
+++ b/flat/BaseRootTunnel.sol
@@ -1329,7 +1329,6 @@ pragma solidity ^0.6.6;
 
 
 
-
 abstract contract BaseRootTunnel is AccessControlMixin {
     using RLPReader for bytes;
     using RLPReader for RLPReader.RLPItem;
diff --git a/flat/ChildMintableERC721.sol b/flat/ChildMintableERC721.sol
index 651d2108..5618fcf6 100644
--- a/flat/ChildMintableERC721.sol
+++ b/flat/ChildMintableERC721.sol
@@ -2120,6 +2120,10 @@ contract ChildMintableERC721 is
     bytes32 public constant DEPOSITOR_ROLE = keccak256("DEPOSITOR_ROLE");
     mapping (uint256 => bool) public withdrawnTokens;
 
+    // limit batching of tokens due to gas limit restrictions
+    uint256 public constant BATCH_LIMIT = 20;
+
+    event WithdrawnBatch(address indexed user, uint256[] tokenIds);
     event TransferWithMetadata(address indexed from, address indexed to, uint256 indexed tokenId, bytes metaData);
 
     constructor(
@@ -2147,20 +2151,34 @@ contract ChildMintableERC721 is
     /**
      * @notice called when token is deposited on root chain
      * @dev Should be callable only by ChildChainManager
-     * Should handle deposit by minting the required tokenId for user
+     * Should handle deposit by minting the required tokenId(s) for user
      * Should set `withdrawnTokens` mapping to `false` for the tokenId being deposited
      * Minting can also be done by other functions
      * @param user user address for whom deposit is being done
-     * @param depositData abi encoded tokenId
+     * @param depositData abi encoded tokenIds. Batch deposit also supported.
      */
     function deposit(address user, bytes calldata depositData)
         external
         override
         only(DEPOSITOR_ROLE)
     {
-        uint256 tokenId = abi.decode(depositData, (uint256));
-        withdrawnTokens[tokenId] = false;
-        _mint(user, tokenId);
+
+        // deposit single
+        if (depositData.length == 32) {
+            uint256 tokenId = abi.decode(depositData, (uint256));
+            withdrawnTokens[tokenId] = false;
+            _mint(user, tokenId);
+
+        // deposit batch
+        } else {
+            uint256[] memory tokenIds = abi.decode(depositData, (uint256[]));
+            uint256 length = tokenIds.length;
+            for (uint256 i; i < length; i++) {
+                withdrawnTokens[tokenIds[i]] = false;
+                _mint(user, tokenIds[i]);
+            }
+        }
+
     }
 
     /**
@@ -2176,15 +2194,41 @@ contract ChildMintableERC721 is
         _burn(tokenId);
     }
 
+    /**
+     * @notice called when user wants to withdraw multiple tokens back to root chain
+     * @dev Should burn user's tokens. This transaction will be verified when exiting on root chain
+     * @param tokenIds tokenId list to withdraw
+     */
+    function withdrawBatch(uint256[] calldata tokenIds) external {
+
+        uint256 length = tokenIds.length;
+        require(length <= BATCH_LIMIT, "ChildMintableERC721: EXCEEDS_BATCH_LIMIT");
+
+        // Iteratively burn ERC721 tokens, for performing
+        // batch withdraw
+        for (uint256 i; i < length; i++) {
+
+            uint256 tokenId = tokenIds[i];
+
+            require(_msgSender() == ownerOf(tokenId), string(abi.encodePacked("ChildMintableERC721: INVALID_TOKEN_OWNER ", tokenId)));
+            withdrawnTokens[tokenId] = true;
+            _burn(tokenId);
+
+        }
+
+        // At last emit this event, which will be used
+        // in MintableERC721 predicate contract on L1
+        // while verifying burn proof
+        emit WithdrawnBatch(_msgSender(), tokenIds);
+
+    }
+
     /**
      * @notice called when user wants to withdraw token back to root chain with token URI
      * @dev Should handle withraw by burning user's token.
      * Should set `withdrawnTokens` mapping to `true` for the tokenId being withdrawn
      * This transaction will be verified when exiting on root chain
      *
-     * Before calling this function, you may want calling `encodeTokenMetadata`
-     * and get metadata to be transferred from L2 to L1 during exit
-     *
      * @param tokenId tokenId to withdraw
      */
     function withdrawWithMetadata(uint256 tokenId) external {
diff --git a/flat/MintableERC721Predicate.sol b/flat/MintableERC721Predicate.sol
index 4f0ad4f9..33445dfd 100644
--- a/flat/MintableERC721Predicate.sol
+++ b/flat/MintableERC721Predicate.sol
@@ -1209,10 +1209,15 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
     bytes32 public constant MANAGER_ROLE = 0x241ecf16d79d0f8dbfb92cbc07fe17840425976cf0667f022fe9877caa831b08;
     // keccak256("MintableERC721")
     bytes32 public constant TOKEN_TYPE = 0xd4392723c111fcb98b073fe55873efb447bcd23cd3e49ec9ea2581930cd01ddc;
-    // keccak("Transfer(address,address,uint256)")
+    // keccak256("Transfer(address,address,uint256)")
     bytes32 public constant TRANSFER_EVENT_SIG = 0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef;
-    // keccak("TransferWithMetadata(address,address,uint256,string)")
-    bytes32 public constant TRANSFER_WITH_METADATA_EVENT_SIG = 0xf3c6803764de9a0fc1c2acb6a71f53407c5e2b9a3e04973e6586da23d64ecaa5;
+    // keccak256("WithdrawnBatch(address,uint256[])")
+    bytes32 public constant WITHDRAW_BATCH_EVENT_SIG = 0xf871896b17e9cb7a64941c62c188a4f5c621b86800e3d15452ece01ce56073df;
+    // keccak256("TransferWithMetadata(address,address,uint256,bytes)")
+    bytes32 public constant TRANSFER_WITH_METADATA_EVENT_SIG = 0xf94915c6d1fd521cee85359239227480c7e8776d7caf1fc3bacad5c269b66a14;
+
+    // limit batching of tokens due to gas limit restrictions
+    uint256 public constant BATCH_LIMIT = 20;
 
     event LockedMintableERC721(
         address indexed depositor,
@@ -1221,6 +1226,13 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
         uint256 tokenId
     );
 
+    event LockedMintableERC721Batch(
+        address indexed depositor,
+        address indexed depositReceiver,
+        address indexed rootToken,
+        uint256[] tokenIds
+    );
+
     constructor() public {}
 
     function initialize(address _owner) external initializer {
@@ -1246,11 +1258,11 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
     }
 
     /**
-     * @notice Lock ERC721 tokens for deposit, callable only by manager
+     * @notice Lock ERC721 token(s) for deposit, callable only by manager
      * @param depositor Address who wants to deposit token
      * @param depositReceiver Address (address) who wants to receive token on child chain
      * @param rootToken Token which gets deposited
-     * @param depositData ABI encoded tokenId
+     * @param depositData ABI encoded tokenId(s). It's possible to deposit batch of tokens.
      */
     function lockTokens(
         address depositor,
@@ -1262,9 +1274,43 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
         override
         only(MANAGER_ROLE)
     {
-        uint256 tokenId = abi.decode(depositData, (uint256));
-        emit LockedMintableERC721(depositor, depositReceiver, rootToken, tokenId);
-        IMintableERC721(rootToken).safeTransferFrom(depositor, address(this), tokenId);
+
+        // Locking single ERC721 token
+        if (depositData.length == 32) {
+
+            uint256 tokenId = abi.decode(depositData, (uint256));
+
+            // Emitting event that single token is getting locked in predicate
+            emit LockedMintableERC721(depositor, depositReceiver, rootToken, tokenId);
+
+            // Transferring token to this address, which will be
+            // released when attempted to be unlocked
+            IMintableERC721(rootToken).safeTransferFrom(depositor, address(this), tokenId);
+
+        } else {
+            // Locking a set a ERC721 token(s)
+
+            uint256[] memory tokenIds = abi.decode(depositData, (uint256[]));
+
+            // Emitting event that a set of ERC721 tokens are getting lockec
+            // in this predicate contract
+            emit LockedMintableERC721Batch(depositor, depositReceiver, rootToken, tokenIds);
+
+            // These many tokens are attempted to be deposited
+            // by user
+            uint256 length = tokenIds.length;
+            require(length <= BATCH_LIMIT, "MintableERC721Predicate: EXCEEDS_BATCH_LIMIT");
+
+            // Iteratively trying to transfer ERC721 token
+            // to this predicate address
+            for (uint256 i; i < length; i++) {
+
+                IMintableERC721(rootToken).safeTransferFrom(depositor, address(this), tokenIds[i]);
+
+            }
+
+        }
+
     }
 
     /**
@@ -1311,6 +1357,46 @@ contract MintableERC721Predicate is ITokenPredicate, AccessControlMixin, Initial
                 token.mint(withdrawer, tokenId);
             }
 
+        } else if (bytes32(logTopicRLPList[0].toUint()) == WITHDRAW_BATCH_EVENT_SIG) { // topic0 is event sig
+            // If it's a simple batch exit, where a set of
+            // ERC721s were burnt in child chain with event signature
+            // looking like `WithdrawnBatch(address indexed user, uint256[] tokenIds);`
+            //
+            // @note This doesn't allow transfer of metadata cross chain
+            // For that check below `else if` block
+
+            address withdrawer = address(logTopicRLPList[1].toUint()); // topic1 is from address
+
+            // RLP encoded tokenId list
+            bytes memory logData = logRLPList[2].toBytes();
+
+            (uint256[] memory tokenIds) = abi.decode(logData, (uint256[]));
+            uint256 length = tokenIds.length;
+
+            IMintableERC721 token = IMintableERC721(rootToken);
+
+            for (uint256 i; i < length; i++) {
+
+                uint256 tokenId = tokenIds[i];
+
+                // Check if token exists or not
+                //
+                // If does, transfer token to withdrawer
+                if (token.exists(tokenId)) {
+                    token.safeTransferFrom(
+                        address(this),
+                        withdrawer,
+                        tokenId
+                    );
+                } else {
+                    // If token was minted on L2
+                    // we'll mint it here, on L1, during
+                    // exiting from L2
+                    token.mint(withdrawer, tokenId);
+                }
+
+            }
+
         } else if (bytes32(logTopicRLPList[0].toUint()) == TRANSFER_WITH_METADATA_EVENT_SIG) { 
             // If this is NFT exit with metadata i.e. URI 👆
             //
diff --git a/flat/RootTunnel.sol b/flat/RootTunnel.sol
index 791a40ee..ec980274 100644
--- a/flat/RootTunnel.sol
+++ b/flat/RootTunnel.sol
@@ -1329,7 +1329,6 @@ pragma solidity ^0.6.6;
 
 
 
-
 abstract contract BaseRootTunnel is AccessControlMixin {
     using RLPReader for bytes;
     using RLPReader for RLPReader.RLPItem;

From d6b00ba4c7ad2cdab5d1c7a5e95dd88b8ac7c0b8 Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 18:50:36 +0530
Subject: [PATCH 08/16] gen: artifacts

---
 artifacts/ChildMintableERC721.json | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/artifacts/ChildMintableERC721.json b/artifacts/ChildMintableERC721.json
index bff1e644..122eb1f2 100644
--- a/artifacts/ChildMintableERC721.json
+++ b/artifacts/ChildMintableERC721.json
@@ -1 +1 @@
-{"abi":[{"inputs":[{"internalType":"string","name":"name_","type":"string"},{"internalType":"string","name":"symbol_","type":"string"},{"internalType":"address","name":"childChainManager","type":"address"}],"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"approved","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"operator","type":"address"},{"indexed":false,"internalType":"bool","name":"approved","type":"bool"}],"name":"ApprovalForAll","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"internalType":"address","name":"userAddress","type":"address"},{"indexed":false,"internalType":"address payable","name":"relayerAddress","type":"address"},{"indexed":false,"internalType":"bytes","name":"functionSignature","type":"bytes"}],"name":"MetaTransactionExecuted","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"bytes32","name":"role","type":"bytes32"},{"indexed":true,"internalType":"bytes32","name":"previousAdminRole","type":"bytes32"},{"indexed":true,"internalType":"bytes32","name":"newAdminRole","type":"bytes32"}],"name":"RoleAdminChanged","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"bytes32","name":"role","type":"bytes32"},{"indexed":true,"internalType":"address","name":"account","type":"address"},{"indexed":true,"internalType":"address","name":"sender","type":"address"}],"name":"RoleGranted","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"bytes32","name":"role","type":"bytes32"},{"indexed":true,"internalType":"address","name":"account","type":"address"},{"indexed":true,"internalType":"address","name":"sender","type":"address"}],"name":"RoleRevoked","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"Transfer","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"},{"indexed":false,"internalType":"bytes","name":"metaData","type":"bytes"}],"name":"TransferWithMetadata","type":"event"},{"inputs":[],"name":"DEFAULT_ADMIN_ROLE","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"DEPOSITOR_ROLE","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"ERC712_VERSION","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"approve","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"baseURI","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"userAddress","type":"address"},{"internalType":"bytes","name":"functionSignature","type":"bytes"},{"internalType":"bytes32","name":"sigR","type":"bytes32"},{"internalType":"bytes32","name":"sigS","type":"bytes32"},{"internalType":"uint8","name":"sigV","type":"uint8"}],"name":"executeMetaTransaction","outputs":[{"internalType":"bytes","name":"","type":"bytes"}],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"getApproved","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"getChainId","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"pure","type":"function"},{"inputs":[],"name":"getDomainSeperator","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"user","type":"address"}],"name":"getNonce","outputs":[{"internalType":"uint256","name":"nonce","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"}],"name":"getRoleAdmin","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"},{"internalType":"uint256","name":"index","type":"uint256"}],"name":"getRoleMember","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"}],"name":"getRoleMemberCount","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"},{"internalType":"address","name":"account","type":"address"}],"name":"grantRole","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"},{"internalType":"address","name":"account","type":"address"}],"name":"hasRole","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"address","name":"operator","type":"address"}],"name":"isApprovedForAll","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"name","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"ownerOf","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"},{"internalType":"address","name":"account","type":"address"}],"name":"renounceRole","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"},{"internalType":"address","name":"account","type":"address"}],"name":"revokeRole","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"safeTransferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"},{"internalType":"bytes","name":"_data","type":"bytes"}],"name":"safeTransferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"operator","type":"address"},{"internalType":"bool","name":"approved","type":"bool"}],"name":"setApprovalForAll","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"bytes4","name":"interfaceId","type":"bytes4"}],"name":"supportsInterface","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"symbol","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"index","type":"uint256"}],"name":"tokenByIndex","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"uint256","name":"index","type":"uint256"}],"name":"tokenOfOwnerByIndex","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"tokenURI","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"totalSupply","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"transferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"","type":"uint256"}],"name":"withdrawnTokens","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"user","type":"address"},{"internalType":"bytes","name":"depositData","type":"bytes"}],"name":"deposit","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"withdraw","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"withdrawWithMetadata","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"encodeTokenMetadata","outputs":[{"internalType":"bytes","name":"","type":"bytes"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"user","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"mint","outputs":[],"stateMutability":"nonpayable","type":"function"}]}
+{"abi":[{"inputs":[{"internalType":"string","name":"name_","type":"string"},{"internalType":"string","name":"symbol_","type":"string"},{"internalType":"address","name":"childChainManager","type":"address"}],"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"approved","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"operator","type":"address"},{"indexed":false,"internalType":"bool","name":"approved","type":"bool"}],"name":"ApprovalForAll","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"internalType":"address","name":"userAddress","type":"address"},{"indexed":false,"internalType":"address payable","name":"relayerAddress","type":"address"},{"indexed":false,"internalType":"bytes","name":"functionSignature","type":"bytes"}],"name":"MetaTransactionExecuted","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"bytes32","name":"role","type":"bytes32"},{"indexed":true,"internalType":"bytes32","name":"previousAdminRole","type":"bytes32"},{"indexed":true,"internalType":"bytes32","name":"newAdminRole","type":"bytes32"}],"name":"RoleAdminChanged","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"bytes32","name":"role","type":"bytes32"},{"indexed":true,"internalType":"address","name":"account","type":"address"},{"indexed":true,"internalType":"address","name":"sender","type":"address"}],"name":"RoleGranted","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"bytes32","name":"role","type":"bytes32"},{"indexed":true,"internalType":"address","name":"account","type":"address"},{"indexed":true,"internalType":"address","name":"sender","type":"address"}],"name":"RoleRevoked","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"Transfer","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"},{"indexed":false,"internalType":"bytes","name":"metaData","type":"bytes"}],"name":"TransferWithMetadata","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"user","type":"address"},{"indexed":false,"internalType":"uint256[]","name":"tokenIds","type":"uint256[]"}],"name":"WithdrawnBatch","type":"event"},{"inputs":[],"name":"BATCH_LIMIT","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"DEFAULT_ADMIN_ROLE","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"DEPOSITOR_ROLE","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"ERC712_VERSION","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"approve","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"baseURI","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"userAddress","type":"address"},{"internalType":"bytes","name":"functionSignature","type":"bytes"},{"internalType":"bytes32","name":"sigR","type":"bytes32"},{"internalType":"bytes32","name":"sigS","type":"bytes32"},{"internalType":"uint8","name":"sigV","type":"uint8"}],"name":"executeMetaTransaction","outputs":[{"internalType":"bytes","name":"","type":"bytes"}],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"getApproved","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"getChainId","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"pure","type":"function"},{"inputs":[],"name":"getDomainSeperator","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"user","type":"address"}],"name":"getNonce","outputs":[{"internalType":"uint256","name":"nonce","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"}],"name":"getRoleAdmin","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"},{"internalType":"uint256","name":"index","type":"uint256"}],"name":"getRoleMember","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"}],"name":"getRoleMemberCount","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"},{"internalType":"address","name":"account","type":"address"}],"name":"grantRole","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"},{"internalType":"address","name":"account","type":"address"}],"name":"hasRole","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"address","name":"operator","type":"address"}],"name":"isApprovedForAll","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"name","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"ownerOf","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"},{"internalType":"address","name":"account","type":"address"}],"name":"renounceRole","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"},{"internalType":"address","name":"account","type":"address"}],"name":"revokeRole","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"safeTransferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"},{"internalType":"bytes","name":"_data","type":"bytes"}],"name":"safeTransferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"operator","type":"address"},{"internalType":"bool","name":"approved","type":"bool"}],"name":"setApprovalForAll","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"bytes4","name":"interfaceId","type":"bytes4"}],"name":"supportsInterface","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"symbol","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"index","type":"uint256"}],"name":"tokenByIndex","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"uint256","name":"index","type":"uint256"}],"name":"tokenOfOwnerByIndex","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"tokenURI","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"totalSupply","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"transferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"","type":"uint256"}],"name":"withdrawnTokens","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"user","type":"address"},{"internalType":"bytes","name":"depositData","type":"bytes"}],"name":"deposit","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"withdraw","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256[]","name":"tokenIds","type":"uint256[]"}],"name":"withdrawBatch","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"withdrawWithMetadata","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"encodeTokenMetadata","outputs":[{"internalType":"bytes","name":"","type":"bytes"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"user","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"mint","outputs":[],"stateMutability":"nonpayable","type":"function"}]}

From eabd017286fbd3313ee666d618989e8393fcbe4f Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 19:38:53 +0530
Subject: [PATCH 09/16] new: metadata setter method in dummy root ERC721
 contract

---
 contracts/root/RootToken/DummyERC721.sol | 28 ++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/contracts/root/RootToken/DummyERC721.sol b/contracts/root/RootToken/DummyERC721.sol
index d7331dc9..2e9a2881 100644
--- a/contracts/root/RootToken/DummyERC721.sol
+++ b/contracts/root/RootToken/DummyERC721.sol
@@ -1,18 +1,25 @@
 pragma solidity 0.6.6;
 
 import {ERC721} from "@openzeppelin/contracts/token/ERC721/ERC721.sol";
+import {AccessControlMixin} from "../../common/AccessControlMixin.sol";
 import {NativeMetaTransaction} from "../../common/NativeMetaTransaction.sol";
 import {ContextMixin} from "../../common/ContextMixin.sol";
 
 contract DummyERC721 is
     ERC721,
+    AccessControlMixin,
     NativeMetaTransaction,
     ContextMixin
 {
+    bytes32 public constant PREDICATE_ROLE = keccak256("PREDICATE_ROLE");
+
     constructor(string memory name_, string memory symbol_)
         public
         ERC721(name_, symbol_)
     {
+        _setupContractId("DummyERC721");
+        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
+        _setupRole(PREDICATE_ROLE, _msgSender());
         _initializeEIP712(name_);
     }
 
@@ -20,6 +27,27 @@ contract DummyERC721 is
         _mint(_msgSender(), tokenId);
     }
 
+    /**
+     * If you're attempting to bring metadata associated with token
+     * from L2 to L1, you must implement this method
+     *
+     * To be invoked when attempting to exit ERC721 with metadata from L2
+     *
+     * `data` is nothing but arbitrary byte array which
+     * is brought in L1, by event emitted in L2, during withdraw
+     */
+    function setTokenMetadata(uint256 tokenId, bytes calldata data) external virtual only(PREDICATE_ROLE) {
+        // This function should decode metadata obtained from L2
+        // and attempt to set it for this `tokenId`
+        //
+        // Following is just a default implementation, feel
+        // free to define your own encoding/ decoding scheme
+        // for L2 -> L1 token metadata transfer
+        string memory uri = abi.decode(data, (string));
+
+        _setTokenURI(tokenId, uri);
+    }
+
     function _msgSender()
         internal
         override

From 5360f9f4078c0612f98d6ee57f988735cd1c8c00 Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 19:58:54 +0530
Subject: [PATCH 10/16] new: interface root tokens are supposed to be
 implementing

---
 contracts/root/RootToken/IRootERC721.sol | 12 ++++++++++++
 1 file changed, 12 insertions(+)
 create mode 100644 contracts/root/RootToken/IRootERC721.sol

diff --git a/contracts/root/RootToken/IRootERC721.sol b/contracts/root/RootToken/IRootERC721.sol
new file mode 100644
index 00000000..99f275f3
--- /dev/null
+++ b/contracts/root/RootToken/IRootERC721.sol
@@ -0,0 +1,12 @@
+import {IERC721} from "@openzeppelin/contracts/token/ERC721/IERC721.sol";
+
+pragma solidity 0.6.6;
+
+interface IRootERC721 is IERC721 {
+
+    // Make sure you implement this method is root ERC721
+    // contract when you're interested in transferring
+    // metadata from L2 to L1
+    function setTokenMetadata(uint256 tokenId, bytes calldata data) external;
+
+}

From 43da361a04b54700ddee4e6962e2d8408f88f6ea Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 20:15:43 +0530
Subject: [PATCH 11/16] new: ERC721 predicate having ability to handle burn
 with metadata signature

---
 contracts/root/RootToken/DummyERC721.sol      | 13 ++++---
 .../root/TokenPredicates/ERC721Predicate.sol  | 36 ++++++++++++++++---
 2 files changed, 37 insertions(+), 12 deletions(-)

diff --git a/contracts/root/RootToken/DummyERC721.sol b/contracts/root/RootToken/DummyERC721.sol
index 2e9a2881..3fdf9424 100644
--- a/contracts/root/RootToken/DummyERC721.sol
+++ b/contracts/root/RootToken/DummyERC721.sol
@@ -1,25 +1,21 @@
 pragma solidity 0.6.6;
 
 import {ERC721} from "@openzeppelin/contracts/token/ERC721/ERC721.sol";
-import {AccessControlMixin} from "../../common/AccessControlMixin.sol";
 import {NativeMetaTransaction} from "../../common/NativeMetaTransaction.sol";
+import {IRootERC721} from "./IRootERC721.sol";
 import {ContextMixin} from "../../common/ContextMixin.sol";
 
 contract DummyERC721 is
     ERC721,
     AccessControlMixin,
     NativeMetaTransaction,
+    IRootERC721,
     ContextMixin
 {
-    bytes32 public constant PREDICATE_ROLE = keccak256("PREDICATE_ROLE");
-
     constructor(string memory name_, string memory symbol_)
         public
         ERC721(name_, symbol_)
     {
-        _setupContractId("DummyERC721");
-        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
-        _setupRole(PREDICATE_ROLE, _msgSender());
         _initializeEIP712(name_);
     }
 
@@ -35,8 +31,11 @@ contract DummyERC721 is
      *
      * `data` is nothing but arbitrary byte array which
      * is brought in L1, by event emitted in L2, during withdraw
+     *
+     * @note Make sure this method is always callable by Predicate contract
+     * who will invoke it when attempting to exit with metadata
      */
-    function setTokenMetadata(uint256 tokenId, bytes calldata data) external virtual only(PREDICATE_ROLE) {
+    function setTokenMetadata(uint256 tokenId, bytes calldata data) external virtual {
         // This function should decode metadata obtained from L2
         // and attempt to set it for this `tokenId`
         //
diff --git a/contracts/root/TokenPredicates/ERC721Predicate.sol b/contracts/root/TokenPredicates/ERC721Predicate.sol
index d97fa247..f94ebbf5 100644
--- a/contracts/root/TokenPredicates/ERC721Predicate.sol
+++ b/contracts/root/TokenPredicates/ERC721Predicate.sol
@@ -1,6 +1,6 @@
 pragma solidity 0.6.6;
 
-import {IERC721} from "@openzeppelin/contracts/token/ERC721/IERC721.sol";
+import {IRootERC721} from "../RootToken/IRootERC721.sol";
 import {IERC721Receiver} from "@openzeppelin/contracts/token/ERC721/IERC721Receiver.sol";
 import {RLPReader} from "../../lib/RLPReader.sol";
 import {ITokenPredicate} from "./ITokenPredicate.sol";
@@ -13,8 +13,12 @@ contract ERC721Predicate is ITokenPredicate, AccessControlMixin, Initializable,
 
     bytes32 public constant MANAGER_ROLE = keccak256("MANAGER_ROLE");
     bytes32 public constant TOKEN_TYPE = keccak256("ERC721");
+    // keccak256("Transfer(address,address,uint256)")
     bytes32 public constant TRANSFER_EVENT_SIG = 0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef;
+    // keccak256("WithdrawnBatch(address,uint256[])")
     bytes32 public constant WITHDRAW_BATCH_EVENT_SIG = 0xf871896b17e9cb7a64941c62c188a4f5c621b86800e3d15452ece01ce56073df;
+    // keccak256("TransferWithMetadata(address,address,uint256,bytes)")
+    bytes32 public constant TRANSFER_WITH_METADATA_EVENT_SIG = 0xf94915c6d1fd521cee85359239227480c7e8776d7caf1fc3bacad5c269b66a14;
 
     // limit batching of tokens due to gas limit restrictions
     uint256 public constant BATCH_LIMIT = 20;
@@ -77,7 +81,7 @@ contract ERC721Predicate is ITokenPredicate, AccessControlMixin, Initializable,
         if (depositData.length == 32) {
             uint256 tokenId = abi.decode(depositData, (uint256));
             emit LockedERC721(depositor, depositReceiver, rootToken, tokenId);
-            IERC721(rootToken).safeTransferFrom(depositor, address(this), tokenId);
+            IRootERC721(rootToken).safeTransferFrom(depositor, address(this), tokenId);
 
         // deposit batch
         } else {
@@ -86,7 +90,7 @@ contract ERC721Predicate is ITokenPredicate, AccessControlMixin, Initializable,
             uint256 length = tokenIds.length;
             require(length <= BATCH_LIMIT, "ERC721Predicate: EXCEEDS_BATCH_LIMIT");
             for (uint256 i; i < length; i++) {
-                IERC721(rootToken).safeTransferFrom(depositor, address(this), tokenIds[i]);
+                IRootERC721(rootToken).safeTransferFrom(depositor, address(this), tokenIds[i]);
             }
         }
     }
@@ -117,7 +121,7 @@ contract ERC721Predicate is ITokenPredicate, AccessControlMixin, Initializable,
                 "ERC721Predicate: INVALID_RECEIVER"
             );
 
-            IERC721(rootToken).safeTransferFrom(
+            IRootERC721(rootToken).safeTransferFrom(
                 address(this),
                 withdrawer,
                 logTopicRLPList[3].toUint() // topic3 is tokenId field
@@ -128,9 +132,31 @@ contract ERC721Predicate is ITokenPredicate, AccessControlMixin, Initializable,
             (uint256[] memory tokenIds) = abi.decode(logData, (uint256[])); // data is tokenId list
             uint256 length = tokenIds.length;
             for (uint256 i; i < length; i++) {
-                IERC721(rootToken).safeTransferFrom(address(this), withdrawer, tokenIds[i]);
+                IRootERC721(rootToken).safeTransferFrom(address(this), withdrawer, tokenIds[i]);
             }
 
+        } else if (bytes32(logTopicRLPList[0].toUint()) == TRANSFER_WITH_METADATA_EVENT_SIG) { 
+            // If this is when NFT exit is done with arbitrary metadata on L2
+
+            address withdrawer = address(logTopicRLPList[1].toUint()); // topic1 is from address
+
+            require(
+                address(logTopicRLPList[2].toUint()) == address(0), // topic2 is to address
+                "ERC721Predicate: INVALID_RECEIVER"
+            );
+
+            IERC721 token = IRootERC721(rootToken);
+            uint256 tokenId = logTopicRLPList[3].toUint(); // topic3 is tokenId field
+
+            token.safeTransferFrom(address(this), withdrawer, tokenId);
+            // This function will be invoked for passing arbitrary
+            // metadata, obtained from event emitted in L2, to
+            // L1 ERC721, so that it can decode & do further processing
+            //
+            // @note Make sure you've implemented this method
+            // if you're interested in exiting with metadata
+            token.setTokenMetadata(tokenId, logRLPList[2].toBytes());
+
         } else {
             revert("ERC721Predicate: INVALID_SIGNATURE");
         }

From 49f48494126f993d4c53d7bc8ff1c97ed8853117 Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 20:16:45 +0530
Subject: [PATCH 12/16] new: dummy child ERC721 token with withdrawWithMetadata

---
 contracts/child/ChildToken/ChildERC721.sol | 43 ++++++++++++++++++++--
 1 file changed, 39 insertions(+), 4 deletions(-)

diff --git a/contracts/child/ChildToken/ChildERC721.sol b/contracts/child/ChildToken/ChildERC721.sol
index e53882be..1312d3f6 100644
--- a/contracts/child/ChildToken/ChildERC721.sol
+++ b/contracts/child/ChildToken/ChildERC721.sol
@@ -18,10 +18,8 @@ contract ChildERC721 is
     // limit batching of tokens due to gas limit restrictions
     uint256 public constant BATCH_LIMIT = 20;
 
-    event WithdrawnBatch(
-        address indexed user,
-        uint256[] tokenIds
-    );
+    event WithdrawnBatch(address indexed user, uint256[] tokenIds);
+    event TransferWithMetadata(address indexed from, address indexed to, uint256 indexed tokenId, bytes metaData);
 
     constructor(
         string memory name_,
@@ -98,4 +96,41 @@ contract ChildERC721 is
         }
         emit WithdrawnBatch(_msgSender(), tokenIds);
     }
+
+    /**
+     * @notice called when user wants to withdraw token back to root chain with arbitrary metadata
+     * @dev Should handle withraw by burning user's token.
+     * 
+     * This transaction will be verified when exiting on root chain
+     *
+     * @param tokenId tokenId to withdraw
+     */
+    function withdrawWithMetadata(uint256 tokenId) external {
+
+        require(_msgSender() == ownerOf(tokenId), "ChildERC721: INVALID_TOKEN_OWNER");
+
+        // Encoding metadata associated with tokenId & emitting event
+        emit TransferWithMetadata(_msgSender(), address(0), tokenId, this.encodeTokenMetadata(tokenId));
+
+        _burn(tokenId);
+
+    }
+
+    /**
+     * @notice This method is supposed to be called by client when withdrawing token with metadata
+     * and pass return value of this function as second paramter of `withdrawWithMetadata` method
+     *
+     * It can be overridden by clients to encode data in a different form, which needs to
+     * be decoded back by them correctly during exiting
+     *
+     * @param tokenId Token for which URI to be fetched
+     */
+    function encodeTokenMetadata(uint256 tokenId) external view virtual returns (bytes memory) {
+
+        // You're always free to change this default implementation
+        // and pack more data in byte array which can be decoded back
+        // in L1
+        return abi.encode(tokenURI(tokenId));
+
+    }
 }

From 3dc40e9de0b4649968429982bdaa463a8a4a91d9 Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 20:22:24 +0530
Subject: [PATCH 13/16] chg: properly overriding function

---
 contracts/root/RootToken/DummyERC721.sol           | 5 ++---
 contracts/root/TokenPredicates/ERC721Predicate.sol | 4 +---
 2 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/contracts/root/RootToken/DummyERC721.sol b/contracts/root/RootToken/DummyERC721.sol
index 3fdf9424..09725f2d 100644
--- a/contracts/root/RootToken/DummyERC721.sol
+++ b/contracts/root/RootToken/DummyERC721.sol
@@ -7,7 +7,6 @@ import {ContextMixin} from "../../common/ContextMixin.sol";
 
 contract DummyERC721 is
     ERC721,
-    AccessControlMixin,
     NativeMetaTransaction,
     IRootERC721,
     ContextMixin
@@ -32,10 +31,10 @@ contract DummyERC721 is
      * `data` is nothing but arbitrary byte array which
      * is brought in L1, by event emitted in L2, during withdraw
      *
-     * @note Make sure this method is always callable by Predicate contract
+     * Make sure this method is always callable by Predicate contract
      * who will invoke it when attempting to exit with metadata
      */
-    function setTokenMetadata(uint256 tokenId, bytes calldata data) external virtual {
+    function setTokenMetadata(uint256 tokenId, bytes calldata data) external override {
         // This function should decode metadata obtained from L2
         // and attempt to set it for this `tokenId`
         //
diff --git a/contracts/root/TokenPredicates/ERC721Predicate.sol b/contracts/root/TokenPredicates/ERC721Predicate.sol
index f94ebbf5..5f51f385 100644
--- a/contracts/root/TokenPredicates/ERC721Predicate.sol
+++ b/contracts/root/TokenPredicates/ERC721Predicate.sol
@@ -138,14 +138,12 @@ contract ERC721Predicate is ITokenPredicate, AccessControlMixin, Initializable,
         } else if (bytes32(logTopicRLPList[0].toUint()) == TRANSFER_WITH_METADATA_EVENT_SIG) { 
             // If this is when NFT exit is done with arbitrary metadata on L2
 
-            address withdrawer = address(logTopicRLPList[1].toUint()); // topic1 is from address
-
             require(
                 address(logTopicRLPList[2].toUint()) == address(0), // topic2 is to address
                 "ERC721Predicate: INVALID_RECEIVER"
             );
 
-            IERC721 token = IRootERC721(rootToken);
+            IRootERC721 token = IRootERC721(rootToken);
             uint256 tokenId = logTopicRLPList[3].toUint(); // topic3 is tokenId field
 
             token.safeTransferFrom(address(this), withdrawer, tokenId);

From 360e82950c2161755871993d2d4eebaef66263ea Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 20:22:40 +0530
Subject: [PATCH 14/16] gen: artifacts

---
 artifacts/ChildERC721.json | 2 +-
 artifacts/DummyERC721.json | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/artifacts/ChildERC721.json b/artifacts/ChildERC721.json
index 9d34fe63..5ed68076 100644
--- a/artifacts/ChildERC721.json
+++ b/artifacts/ChildERC721.json
@@ -1 +1 @@
-{"abi":[{"inputs":[{"internalType":"string","name":"name_","type":"string"},{"internalType":"string","name":"symbol_","type":"string"},{"internalType":"address","name":"childChainManager","type":"address"}],"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"approved","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"operator","type":"address"},{"indexed":false,"internalType":"bool","name":"approved","type":"bool"}],"name":"ApprovalForAll","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"internalType":"address","name":"userAddress","type":"address"},{"indexed":false,"internalType":"address payable","name":"relayerAddress","type":"address"},{"indexed":false,"internalType":"bytes","name":"functionSignature","type":"bytes"}],"name":"MetaTransactionExecuted","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"bytes32","name":"role","type":"bytes32"},{"indexed":true,"internalType":"bytes32","name":"previousAdminRole","type":"bytes32"},{"indexed":true,"internalType":"bytes32","name":"newAdminRole","type":"bytes32"}],"name":"RoleAdminChanged","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"bytes32","name":"role","type":"bytes32"},{"indexed":true,"internalType":"address","name":"account","type":"address"},{"indexed":true,"internalType":"address","name":"sender","type":"address"}],"name":"RoleGranted","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"bytes32","name":"role","type":"bytes32"},{"indexed":true,"internalType":"address","name":"account","type":"address"},{"indexed":true,"internalType":"address","name":"sender","type":"address"}],"name":"RoleRevoked","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"Transfer","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"user","type":"address"},{"indexed":false,"internalType":"uint256[]","name":"tokenIds","type":"uint256[]"}],"name":"WithdrawnBatch","type":"event"},{"inputs":[],"name":"BATCH_LIMIT","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"DEFAULT_ADMIN_ROLE","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"DEPOSITOR_ROLE","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"ERC712_VERSION","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"approve","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"baseURI","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"userAddress","type":"address"},{"internalType":"bytes","name":"functionSignature","type":"bytes"},{"internalType":"bytes32","name":"sigR","type":"bytes32"},{"internalType":"bytes32","name":"sigS","type":"bytes32"},{"internalType":"uint8","name":"sigV","type":"uint8"}],"name":"executeMetaTransaction","outputs":[{"internalType":"bytes","name":"","type":"bytes"}],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"getApproved","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"getChainId","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"pure","type":"function"},{"inputs":[],"name":"getDomainSeperator","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"user","type":"address"}],"name":"getNonce","outputs":[{"internalType":"uint256","name":"nonce","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"}],"name":"getRoleAdmin","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"},{"internalType":"uint256","name":"index","type":"uint256"}],"name":"getRoleMember","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"}],"name":"getRoleMemberCount","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"},{"internalType":"address","name":"account","type":"address"}],"name":"grantRole","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"bytes32","name":"role","type":"bytes32"},{"internalType":"address","name":"account","type":"address"}],"name":"hasRole","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type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+{"abi":[{"inputs":[{"internalType":"string","name":"name_","type":"string"},{"internalType":"string","name":"symbol_","type":"string"},{"internalType":"address","name":"childChainManager","type":"address"}],"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"approved","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"operator","type":"address"},{"indexed":false,"internalType":"bool","name":"approved","type":"bool"}],"name":"ApprovalForAll","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"internalType":"address","name":"userAddress","type":"address"},{"indexed":false,"internalType":"address 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diff --git a/artifacts/DummyERC721.json b/artifacts/DummyERC721.json
index 975c6155..79b55a13 100644
--- a/artifacts/DummyERC721.json
+++ b/artifacts/DummyERC721.json
@@ -1 +1 @@
-{"abi":[{"inputs":[{"internalType":"string","name":"name_","type":"string"},{"internalType":"string","name":"symbol_","type":"string"}],"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"approved","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"operator","type":"address"},{"indexed":false,"internalType":"bool","name":"approved","type":"bool"}],"name":"ApprovalForAll","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"internalType":"address","name":"userAddress","type":"address"},{"indexed":false,"internalType":"address payable","name":"relayerAddress","type":"address"},{"indexed":false,"internalType":"bytes","name":"functionSignature","type":"bytes"}],"name":"MetaTransactionExecuted","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"Transfer","type":"event"},{"inputs":[],"name":"ERC712_VERSION","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"approve","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"baseURI","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"userAddress","type":"address"},{"internalType":"bytes","name":"functionSignature","type":"bytes"},{"internalType":"bytes32","name":"sigR","type":"bytes32"},{"internalType":"bytes32","name":"sigS","type":"bytes32"},{"internalType":"uint8","name":"sigV","type":"uint8"}],"name":"executeMetaTransaction","outputs":[{"internalType":"bytes","name":"","type":"bytes"}],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"getApproved","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"getChainId","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"pure","type":"function"},{"inputs":[],"name":"getDomainSeperator","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"user","type":"address"}],"name":"getNonce","outputs":[{"internalType":"uint256","name":"nonce","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"address","name":"operator","type":"address"}],"name":"isApprovedForAll","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"name","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"ownerOf","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"safeTransferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"},{"internalType":"bytes","name":"_data","type":"bytes"}],"name":"safeTransferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"operator","type":"address"},{"internalType":"bool","name":"approved","type":"bool"}],"name":"setApprovalForAll","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"bytes4","name":"interfaceId","type":"bytes4"}],"name":"supportsInterface","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"symbol","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"index","type":"uint256"}],"name":"tokenByIndex","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"uint256","name":"index","type":"uint256"}],"name":"tokenOfOwnerByIndex","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"tokenURI","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"totalSupply","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"transferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"mint","outputs":[],"stateMutability":"nonpayable","type":"function"}]}
+{"abi":[{"inputs":[{"internalType":"string","name":"name_","type":"string"},{"internalType":"string","name":"symbol_","type":"string"}],"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"approved","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"operator","type":"address"},{"indexed":false,"internalType":"bool","name":"approved","type":"bool"}],"name":"ApprovalForAll","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"internalType":"address","name":"userAddress","type":"address"},{"indexed":false,"internalType":"address payable","name":"relayerAddress","type":"address"},{"indexed":false,"internalType":"bytes","name":"functionSignature","type":"bytes"}],"name":"MetaTransactionExecuted","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":true,"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"Transfer","type":"event"},{"inputs":[],"name":"ERC712_VERSION","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"approve","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"baseURI","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"userAddress","type":"address"},{"internalType":"bytes","name":"functionSignature","type":"bytes"},{"internalType":"bytes32","name":"sigR","type":"bytes32"},{"internalType":"bytes32","name":"sigS","type":"bytes32"},{"internalType":"uint8","name":"sigV","type":"uint8"}],"name":"executeMetaTransaction","outputs":[{"internalType":"bytes","name":"","type":"bytes"}],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"getApproved","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"getChainId","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"pure","type":"function"},{"inputs":[],"name":"getDomainSeperator","outputs":[{"internalType":"bytes32","name":"","type":"bytes32"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"user","type":"address"}],"name":"getNonce","outputs":[{"internalType":"uint256","name":"nonce","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"address","name":"operator","type":"address"}],"name":"isApprovedForAll","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"name","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"ownerOf","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"safeTransferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"},{"internalType":"bytes","name":"_data","type":"bytes"}],"name":"safeTransferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"operator","type":"address"},{"internalType":"bool","name":"approved","type":"bool"}],"name":"setApprovalForAll","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"bytes4","name":"interfaceId","type":"bytes4"}],"name":"supportsInterface","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"symbol","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"index","type":"uint256"}],"name":"tokenByIndex","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"uint256","name":"index","type":"uint256"}],"name":"tokenOfOwnerByIndex","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"tokenURI","outputs":[{"internalType":"string","name":"","type":"string"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"totalSupply","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"transferFrom","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"}],"name":"mint","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"uint256","name":"tokenId","type":"uint256"},{"internalType":"bytes","name":"data","type":"bytes"}],"name":"setTokenMetadata","outputs":[],"stateMutability":"nonpayable","type":"function"}]}

From 2cd513ed7081ffe29c49f7722c71dbb0aff5ef91 Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 20:22:52 +0530
Subject: [PATCH 15/16] gen: flattened contracts

---
 flat/ChildERC721.sol     | 43 ++++++++++++++++++++++++++++++++++----
 flat/DummyERC721.sol     | 39 ++++++++++++++++++++++++++++++++++
 flat/ERC721Predicate.sol | 45 ++++++++++++++++++++++++++++++++++++----
 3 files changed, 119 insertions(+), 8 deletions(-)

diff --git a/flat/ChildERC721.sol b/flat/ChildERC721.sol
index 89d5e4e5..83b571eb 100644
--- a/flat/ChildERC721.sol
+++ b/flat/ChildERC721.sol
@@ -2121,10 +2121,8 @@ contract ChildERC721 is
     // limit batching of tokens due to gas limit restrictions
     uint256 public constant BATCH_LIMIT = 20;
 
-    event WithdrawnBatch(
-        address indexed user,
-        uint256[] tokenIds
-    );
+    event WithdrawnBatch(address indexed user, uint256[] tokenIds);
+    event TransferWithMetadata(address indexed from, address indexed to, uint256 indexed tokenId, bytes metaData);
 
     constructor(
         string memory name_,
@@ -2201,4 +2199,41 @@ contract ChildERC721 is
         }
         emit WithdrawnBatch(_msgSender(), tokenIds);
     }
+
+    /**
+     * @notice called when user wants to withdraw token back to root chain with arbitrary metadata
+     * @dev Should handle withraw by burning user's token.
+     * 
+     * This transaction will be verified when exiting on root chain
+     *
+     * @param tokenId tokenId to withdraw
+     */
+    function withdrawWithMetadata(uint256 tokenId) external {
+
+        require(_msgSender() == ownerOf(tokenId), "ChildERC721: INVALID_TOKEN_OWNER");
+
+        // Encoding metadata associated with tokenId & emitting event
+        emit TransferWithMetadata(_msgSender(), address(0), tokenId, this.encodeTokenMetadata(tokenId));
+
+        _burn(tokenId);
+
+    }
+
+    /**
+     * @notice This method is supposed to be called by client when withdrawing token with metadata
+     * and pass return value of this function as second paramter of `withdrawWithMetadata` method
+     *
+     * It can be overridden by clients to encode data in a different form, which needs to
+     * be decoded back by them correctly during exiting
+     *
+     * @param tokenId Token for which URI to be fetched
+     */
+    function encodeTokenMetadata(uint256 tokenId) external view virtual returns (bytes memory) {
+
+        // You're always free to change this default implementation
+        // and pack more data in byte array which can be decoded back
+        // in L1
+        return abi.encode(tokenURI(tokenId));
+
+    }
 }
diff --git a/flat/DummyERC721.sol b/flat/DummyERC721.sol
index 8af96fcc..3bbec2fd 100644
--- a/flat/DummyERC721.sol
+++ b/flat/DummyERC721.sol
@@ -1826,6 +1826,19 @@ contract NativeMetaTransaction is EIP712Base {
     }
 }
 
+// File: contracts/root/RootToken/IRootERC721.sol
+
+pragma solidity 0.6.6;
+
+interface IRootERC721 is IERC721 {
+
+    // Make sure you implement this method is root ERC721
+    // contract when you're interested in transferring
+    // metadata from L2 to L1
+    function setTokenMetadata(uint256 tokenId, bytes calldata data) external;
+
+}
+
 // File: contracts/common/ContextMixin.sol
 
 pragma solidity 0.6.6;
@@ -1860,9 +1873,11 @@ pragma solidity 0.6.6;
 
 
 
+
 contract DummyERC721 is
     ERC721,
     NativeMetaTransaction,
+    IRootERC721,
     ContextMixin
 {
     constructor(string memory name_, string memory symbol_)
@@ -1876,6 +1891,30 @@ contract DummyERC721 is
         _mint(_msgSender(), tokenId);
     }
 
+    /**
+     * If you're attempting to bring metadata associated with token
+     * from L2 to L1, you must implement this method
+     *
+     * To be invoked when attempting to exit ERC721 with metadata from L2
+     *
+     * `data` is nothing but arbitrary byte array which
+     * is brought in L1, by event emitted in L2, during withdraw
+     *
+     * Make sure this method is always callable by Predicate contract
+     * who will invoke it when attempting to exit with metadata
+     */
+    function setTokenMetadata(uint256 tokenId, bytes calldata data) external override {
+        // This function should decode metadata obtained from L2
+        // and attempt to set it for this `tokenId`
+        //
+        // Following is just a default implementation, feel
+        // free to define your own encoding/ decoding scheme
+        // for L2 -> L1 token metadata transfer
+        string memory uri = abi.decode(data, (string));
+
+        _setTokenURI(tokenId, uri);
+    }
+
     function _msgSender()
         internal
         override
diff --git a/flat/ERC721Predicate.sol b/flat/ERC721Predicate.sol
index 5875d7d8..583bac2e 100644
--- a/flat/ERC721Predicate.sol
+++ b/flat/ERC721Predicate.sol
@@ -157,6 +157,19 @@ interface IERC721 is IERC165 {
     function safeTransferFrom(address from, address to, uint256 tokenId, bytes calldata data) external;
 }
 
+// File: contracts/root/RootToken/IRootERC721.sol
+
+pragma solidity 0.6.6;
+
+interface IRootERC721 is IERC721 {
+
+    // Make sure you implement this method is root ERC721
+    // contract when you're interested in transferring
+    // metadata from L2 to L1
+    function setTokenMetadata(uint256 tokenId, bytes calldata data) external;
+
+}
+
 // File: @openzeppelin/contracts/token/ERC721/IERC721Receiver.sol
 
 // SPDX-License-Identifier: MIT
@@ -1172,8 +1185,12 @@ contract ERC721Predicate is ITokenPredicate, AccessControlMixin, Initializable,
 
     bytes32 public constant MANAGER_ROLE = keccak256("MANAGER_ROLE");
     bytes32 public constant TOKEN_TYPE = keccak256("ERC721");
+    // keccak256("Transfer(address,address,uint256)")
     bytes32 public constant TRANSFER_EVENT_SIG = 0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef;
+    // keccak256("WithdrawnBatch(address,uint256[])")
     bytes32 public constant WITHDRAW_BATCH_EVENT_SIG = 0xf871896b17e9cb7a64941c62c188a4f5c621b86800e3d15452ece01ce56073df;
+    // keccak256("TransferWithMetadata(address,address,uint256,bytes)")
+    bytes32 public constant TRANSFER_WITH_METADATA_EVENT_SIG = 0xf94915c6d1fd521cee85359239227480c7e8776d7caf1fc3bacad5c269b66a14;
 
     // limit batching of tokens due to gas limit restrictions
     uint256 public constant BATCH_LIMIT = 20;
@@ -1236,7 +1253,7 @@ contract ERC721Predicate is ITokenPredicate, AccessControlMixin, Initializable,
         if (depositData.length == 32) {
             uint256 tokenId = abi.decode(depositData, (uint256));
             emit LockedERC721(depositor, depositReceiver, rootToken, tokenId);
-            IERC721(rootToken).safeTransferFrom(depositor, address(this), tokenId);
+            IRootERC721(rootToken).safeTransferFrom(depositor, address(this), tokenId);
 
         // deposit batch
         } else {
@@ -1245,7 +1262,7 @@ contract ERC721Predicate is ITokenPredicate, AccessControlMixin, Initializable,
             uint256 length = tokenIds.length;
             require(length <= BATCH_LIMIT, "ERC721Predicate: EXCEEDS_BATCH_LIMIT");
             for (uint256 i; i < length; i++) {
-                IERC721(rootToken).safeTransferFrom(depositor, address(this), tokenIds[i]);
+                IRootERC721(rootToken).safeTransferFrom(depositor, address(this), tokenIds[i]);
             }
         }
     }
@@ -1276,7 +1293,7 @@ contract ERC721Predicate is ITokenPredicate, AccessControlMixin, Initializable,
                 "ERC721Predicate: INVALID_RECEIVER"
             );
 
-            IERC721(rootToken).safeTransferFrom(
+            IRootERC721(rootToken).safeTransferFrom(
                 address(this),
                 withdrawer,
                 logTopicRLPList[3].toUint() // topic3 is tokenId field
@@ -1287,9 +1304,29 @@ contract ERC721Predicate is ITokenPredicate, AccessControlMixin, Initializable,
             (uint256[] memory tokenIds) = abi.decode(logData, (uint256[])); // data is tokenId list
             uint256 length = tokenIds.length;
             for (uint256 i; i < length; i++) {
-                IERC721(rootToken).safeTransferFrom(address(this), withdrawer, tokenIds[i]);
+                IRootERC721(rootToken).safeTransferFrom(address(this), withdrawer, tokenIds[i]);
             }
 
+        } else if (bytes32(logTopicRLPList[0].toUint()) == TRANSFER_WITH_METADATA_EVENT_SIG) { 
+            // If this is when NFT exit is done with arbitrary metadata on L2
+
+            require(
+                address(logTopicRLPList[2].toUint()) == address(0), // topic2 is to address
+                "ERC721Predicate: INVALID_RECEIVER"
+            );
+
+            IRootERC721 token = IRootERC721(rootToken);
+            uint256 tokenId = logTopicRLPList[3].toUint(); // topic3 is tokenId field
+
+            token.safeTransferFrom(address(this), withdrawer, tokenId);
+            // This function will be invoked for passing arbitrary
+            // metadata, obtained from event emitted in L2, to
+            // L1 ERC721, so that it can decode & do further processing
+            //
+            // @note Make sure you've implemented this method
+            // if you're interested in exiting with metadata
+            token.setTokenMetadata(tokenId, logRLPList[2].toBytes());
+
         } else {
             revert("ERC721Predicate: INVALID_SIGNATURE");
         }

From 701a93b8fb2870cc7f2234e21210d11cab8de145 Mon Sep 17 00:00:00 2001
From: Anjan Roy <anjanroy@yandex.com>
Date: Tue, 9 Mar 2021 20:27:32 +0530
Subject: [PATCH 16/16] fix: corrected event signature

---
 test/helpers/constants.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/helpers/constants.js b/test/helpers/constants.js
index 206468c2..6dbe2145 100644
--- a/test/helpers/constants.js
+++ b/test/helpers/constants.js
@@ -17,7 +17,7 @@ export const etherAddress = '0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE'
 
 export const erc20TransferEventSig = '0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef'
 export const erc721TransferEventSig = '0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef'
-export const erc721TransferWithMetadataEventSig = '0xf3c6803764de9a0fc1c2acb6a71f53407c5e2b9a3e04973e6586da23d64ecaa5'
+export const erc721TransferWithMetadataEventSig = '0xf94915c6d1fd521cee85359239227480c7e8776d7caf1fc3bacad5c269b66a14'
 export const erc1155TransferSingleEventSig = '0xc3d58168c5ae7397731d063d5bbf3d657854427343f4c083240f7aacaa2d0f62'
 export const erc1155TransferBatchEventSig = '0x4a39dc06d4c0dbc64b70af90fd698a233a518aa5d07e595d983b8c0526c8f7fb'