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EIPS/eip-7496.md

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+---
+eip: 7496
+title: NFT Dynamic Traits
+description: Extension to ERC-721 and ERC-1155 for dynamic onchain traits
+author: Adam Montgomery (@montasaurus), Ryan Ghods (@ryanio), 0age (@0age), James Wenzel (@jameswenzel), Stephan Min (@stephankmin)
+discussions-to: https://ethereum-magicians.org/t/erc-7496-nft-dynamic-traits/15484
+status: Draft
+type: Standards Track
+category: ERC
+created: 2023-07-28
+requires: 165, 721, 1155
+---
+
+## Abstract
+
+This specification introduces a new interface that extends [ERC-721](./eip-721.md) and [ERC-1155](./eip-1155.md) that defines methods for setting and getting dynamic onchain traits associated with non-fungible tokens. These dynamic traits can be used to represent properties, characteristics, redeemable entitlements, or other attributes that can change over time. By defining these traits onchain, they can be used and modified by other onchain contracts.
+
+## Motivation
+
+Trait values for non-fungible tokens are often stored offchain. This makes it difficult to query and mutate these values in contract code. Specifying the ability to set and get traits onchain allows for new use cases like redeeming onchain entitlements and transacting based on a token's traits.
+
+Onchain traits can be used by contracts in a variety of different scenarios. For example, a contract that wants to entitle a token to a consumable benefit (e.g. a redeemable) can robustly reflect that onchain. Marketplaces can allow bidding on these tokens based on the trait value without having to rely on offchain state and exposing users to frontrunning attacks. The motivating use case behind this proposal is to protect users from frontrunning attacks on marketplaces where users can list NFTs with certain traits where they are expected to be upheld during fulfillment.
+
+This interface for traits was chosen instead of relying on using regular `getFoo()` and `setFoo()` style functions to allow for brevity in defining, setting, and getting traits. Otherwise, contracts would need to know both the getter and setter function selectors including the parameters that go along with it. In defining general but explicit get and set functions, the function signatures are known and only the trait key and values are needed to query and set the values. Contracts can also add new traits in the future without needing to modify contract code.
+
+## Specification
+
+The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 and RFC 8174.
+
+Contracts implementing this EIP MUST include the events, getters, and setters as defined below, and MUST return `true` for [ERC-165](./eip-165.md) `supportsInterface` for `0xaf332f3e`, the 4 byte `interfaceId` for this ERC.
+
+```solidity
+interface IERC7496 {
+    /* Events */
+    event TraitUpdated(bytes32 indexed traitKey, uint256 tokenId, bytes32 traitValue);
+    event TraitUpdatedRange(bytes32 indexed traitKey, uint256 fromTokenId, uint256 toTokenId);
+    event TraitUpdatedRangeUniformValue(bytes32 indexed traitKey, uint256 fromTokenId, uint256 toTokenId, bytes32 traitValue);
+    event TraitUpdatedList(bytes32 indexed traitKey, uint256[] tokenIds);
+    event TraitUpdatedListUniformValue(bytes32 indexed traitKey, uint256[] tokenIds, bytes32 traitValue);
+    event TraitMetadataURIUpdated();
+
+    /* Getters */
+    function getTraitValue(uint256 tokenId, bytes32 traitKey) external view returns (bytes32 traitValue);
+    function getTraitValues(uint256 tokenId, bytes32[] calldata traitKeys) external view returns (bytes32[] traitValues);
+    function getTraitMetadataURI() external view returns (string memory uri);
+
+    /* Setters */
+    function setTrait(uint256 tokenId, bytes32 traitKey, bytes32 newValue) external;
+}
+```
+
+### Keys & Names
+
+The `traitKey` is used to identify a trait. The `traitKey` MUST be a unique `bytes32` value identifying a single trait.
+
+The `traitKey` SHOULD be a `keccak256` hash of a human readable trait name.
+
+### Metadata
+
+Trait metadata is an optional way to define additional information about which traits are present in a contract, how to parse and display trait values, and permissions for setting trait values.
+
+The trait metadata must be compliant with the [specified schema](../assets/eip-7496/DynamicTraitsSchema.json).
+
+The trait metadata URI MAY be a data URI or point to an offchain resource.
+
+The keys in the `traits` object MUST be unique trait names. If the trait name is 32 byte hex string starting with `0x` then it is interpreted as a literal `traitKey`. Otherwise, the `traitKey` is defined as the `keccak256` hash of the trait name. A literal `traitKey` MUST NOT collide with the `keccak256` hash of any other traits defined in the metadata.
+
+The `displayName` values MUST be unique and MUST NOT collide with the `displayName` of any other traits defined in the metadata.
+
+The `validateOnSale` value provides a signal to marketplaces on how to validate the trait value when a token is being sold. If the validation criteria is not met, the sale MUST not be permitted by the marketplace contract. If specified, the value of `validateOnSale` MUST be one of the following (or it is assumed to be `none`):
+
+- `none`: No validation is necessary.
+- `requireEq`: The `bytes32` `traitValue` MUST be equal to the value at the time the offer to purchase was made.
+- `requireUintGte`: The `bytes32` `traitValue` MUST be greater than or equal to the value at the time the offer to purchase was made. This comparison is made using the `uint256` representation of the `bytes32` value.
+- `requireUintLte`: The `bytes32` `traitValue` MUST be less than or equal to the value at the time the offer to purchase was made. This comparison is made using the `uint256` representation of the `bytes32` value.
+
+Note that even though this specification requires marketplaces to validate the required trait values, buyers and sellers cannot fully rely on marketplaces to do this and must also take their own precautions to research the current trait values prior to initiating the transaction.
+
+Here is an example of the specified schema:
+
+```json
+{
+  "traits": {
+    "color": {
+      "displayName": "Color",
+      "dataType": {
+        "type": "string",
+        "acceptableValues": ["red", "green", "blue"]
+      }
+    },
+    "points": {
+      "displayName": "Total Score",
+      "dataType": {
+        "type": "decimal",
+        "signed": false,
+        "bits": 16,
+        "decimals": 0
+      },
+      "validateOnSale": "requireUintGte"
+    },
+    "name": {
+      "displayName": "Name",
+      "dataType": {
+        "type": "string",
+        "minLength": 1,
+        "maxLength": 32,
+        "valueMappings": {
+          "0x0": "Unnamed",
+          "0x92e75d5e42b80de937d204558acf69c8ea586a244fe88bc0181323fe3b9e3ebf": "🙂"
+        }
+      },
+      "tokenOwnerCanUpdateValue": true
+    },
+    "birthday": {
+      "displayName": "Birthday",
+      "dataType": {
+        "type": "epochSeconds",
+        "valueMappings": {
+          "0x0": null
+        }
+      }
+    },
+    "0x77c2fd45bd8bdef5b5bc773f46759bb8d169f3468caab64d7d5f2db16bb867a8": {
+      "displayName": "🚢 📅",
+      "dataType": {
+        "type": "epochSeconds",
+        "valueMappings": {
+          "0x0": 1696702201
+        }
+      }
+    }
+  }
+}
+```
+
+#### `string` Metadata Type
+
+The `string` metadata type allows for a string value to be set for a trait.
+
+The `dataType` object MAY have a `minLength` and `maxLength` value defined. If `minLength` is not specified, it is assumed to be 0. If `maxLength` is not specified, it is assumed to be a reasonable length.
+
+The `dataType` object MAY have a `valueMappings` object defined. If the `valueMappings` object is defined, the `valueMappings` object MUST be a mapping of `bytes32` values to `string` or unset `null` values. The `bytes32` values SHOULD be the `keccak256` hash of the `string` value. The `string` values MUST be unique.
+
+#### `decimal` Metadata Type
+
+The `decimal` metadata type allows for a numeric value to be set for a trait in decimal form.
+
+The `dataType` object MAY have a `signed` value defined. If `signed` is not specified, it is assumed to be `false`. This determines whether the `traitValue` returned is interpreted as a signed or unsigned integer.
+
+The `dataType` object MAY have a `bits` value defined. If specified, the `bits` value MUST be a positive integer. The `bits` value determines the maximum number of bits that can be used to represent the `traitValue`.
+
+The `dataType` object MAY have a `decimals` value defined. The `decimals` value MUST be a non-negative integer. The `decimals` value determines the number of decimal places included in the `traitValue` returned onchain. The `decimals` value MUST be less than or equal to the `bits` value. If `decimals` is not specified, it is assumed to be 0.
+
+The `dataType` object MAY have a `valueMappings` object defined. If the `valueMappings` object is defined, the `valueMappings` object MUST be a mapping of `bytes32` values to numeric or unset `null` values.
+
+#### `boolean` Metadata Type
+
+The `boolean` metadata type allows for a boolean value to be set for a trait.
+
+The `dataType` object MAY have a `valueMappings` object defined. If the `valueMappings` object is defined, the `valueMappings` object MUST be a mapping of `bytes32` values to `boolean` or unset `null` values. The `boolean` values MUST be unique.
+
+If `valueMappings` is not used, the default trait values for `boolean` should be `bytes32(0)` for `false` and `bytes32(uint256(1))` (`0x0000000000000000000000000000000000000000000000000000000000000001`) for `true`.
+
+#### `epochSeconds` Metadata Type
+
+The `epochSeconds` metadata type allows for a numeric value to be set for a trait in seconds since the Unix epoch.
+
+The `dataType` object MAY have a `valueMappings` object defined. If the `valueMappings` object is defined, the `valueMappings` object MUST be a mapping of `bytes32` values to integer or unset `null` values.
+
+### Events
+
+Updating traits MUST emit one of:
+
+- `TraitUpdated`
+- `TraitUpdatedRange`
+- `TraitUpdatedRangeUniformValue`
+- `TraitUpdatedList`
+- `TraitUpdatedListUniformValue`
+
+For the `Range` events, the `fromTokenId` and `toTokenId` MUST be a consecutive range of tokens IDs and MUST be treated as an inclusive range.
+
+For the `List` events, the `tokenIds` MAY be in any order.
+
+It is RECOMMENDED to use the `UniformValue` events when the trait value is uniform across all token ids, so offchain indexers can more quickly process bulk updates rather than fetching each trait value individually.
+
+Updating the trait metadata MUST emit the event `TraitMetadataURIUpdated` so offchain indexers can be notified to query the contract for the latest changes via `getTraitMetadataURI()`.
+
+### `setTrait`
+
+If a trait defines `tokenOwnerCanUpdateValue` as `true`, then the trait value MUST be updatable by the token owner by calling `setTrait`.
+
+If the value the token owner is attempting to set is not valid, the transaction MUST revert. If the value is valid, the trait value MUST be updated and one of the `TraitUpdated` events MUST be emitted.
+
+If the trait has a `valueMappings` entry defined for the desired value being set, `setTrait` MUST be called with the corresponding `traitValue`.
+
+## Rationale
+
+The design of this specification is primarily a key-value mapping for maximum flexibility.
+
+The traits metadata allows for customizability of both display and behavior. The `valueMappings` property can define human-readable values to enhance the traits, for example, the default label of the `0` value (e.g. if the key was "redeemed", "0" could be mapped to "No", and "1" to "Yes"). The `validateOnSale` property lets the token creator define which traits should be protected on order creation and fulfillment, to protect end users against frontrunning.
+
+## Backwards Compatibility
+
+As a new EIP, no backwards compatibility issues are present, except for the point in the specification above that it is explicitly required that the onchain traits MUST override any conflicting values specified by the ERC-721 or ERC-1155 metadata URIs.
+
+## Test Cases
+
+Authors have included Foundry tests covering functionality of the specification in the [assets folder](../assets/eip-7496/DynamicTraits.t.sol).
+
+## Reference Implementation
+
+Authors have included reference implementations of the specification in the [assets folder](../assets/eip-7496/DynamicTraits.sol).
+
+## Security Considerations
+
+The set\* methods exposed externally MUST be permissioned so they are not callable by everyone but only by select roles or addresses.
+
+Marketplaces SHOULD NOT trust offchain state of traits as they can be frontrunned. Marketplaces SHOULD check the current state of onchain traits at the time of transfer. Marketplaces MAY check certain traits that change the value of the NFT (e.g. redemption status, defined by metadata values with `validateOnSale` property) or they MAY hash all the trait values to guarantee the same state at the time of order creation.
+
+## Copyright
+
+Copyright and related rights waived via [CC0](../LICENSE.md).

assets/eip-7496/DynamicTraits.sol

@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: CC0-1.0
+pragma solidity ^0.8.19;
+
+import {EnumerableSet} from "openzeppelin-contracts/contracts/utils/structs/EnumerableSet.sol";
+import {IERC7496} from "./interfaces/IERC7496.sol";
+
+abstract contract DynamicTraits is IERC7496 {
+    using EnumerableSet for EnumerableSet.Bytes32Set;
+
+    /// @notice Thrown when a new trait value is not different from the existing value
+    error TraitValueUnchanged();
+
+    /// @notice An enumerable set of all trait keys that have been set
+    EnumerableSet.Bytes32Set internal _traitKeys;
+
+    /// @notice A mapping of token ID to a mapping of trait key to trait value
+    mapping(uint256 tokenId => mapping(bytes32 traitKey => bytes32 traitValue)) internal _traits;
+
+    /// @notice An offchain string URI that points to a JSON file containing trait metadata
+    string internal _traitMetadataURI;
+
+    /**
+     * @notice Get the value of a trait for a given token ID.
+     * @param tokenId The token ID to get the trait value for
+     * @param traitKey The trait key to get the value of
+     */
+    function getTraitValue(uint256 tokenId, bytes32 traitKey) public view virtual returns (bytes32 traitValue) {
+        traitValue = _traits[tokenId][traitKey];
+    }
+
+    /**
+     * @notice Get the values of traits for a given token ID.
+     * @param tokenId The token ID to get the trait values for
+     * @param traitKeys The trait keys to get the values of
+     */
+    function getTraitValues(uint256 tokenId, bytes32[] calldata traitKeys)
+        public
+        view
+        virtual
+        returns (bytes32[] memory traitValues)
+    {
+        uint256 length = traitKeys.length;
+        traitValues = new bytes32[](length);
+        for (uint256 i = 0; i < length;) {
+            bytes32 traitKey = traitKeys[i];
+            traitValues[i] = getTraitValue(tokenId, traitKey);
+            unchecked {
+                ++i;
+            }
+        }
+    }
+
+    /**
+     * @notice Get the URI for the trait metadata
+     */
+    function getTraitMetadataURI() external view virtual returns (string memory labelsURI) {
+        return _traitMetadataURI;
+    }
+
+    /**
+     * @notice Set the value of a trait for a given token ID. If newTrait is bytes32(0), sets the zero value hash.
+     *         Reverts if the trait value is the zero value hash.
+     * @param tokenId The token ID to set the trait value for
+     * @param traitKey The trait key to set the value of
+     * @param newValue The new trait value to set
+     */
+    function _setTrait(uint256 tokenId, bytes32 traitKey, bytes32 newValue) internal {
+        bytes32 existingValue = _traits[tokenId][traitKey];
+
+        if (existingValue == newValue) {
+            revert TraitValueUnchanged();
+        }
+
+        // no-op if exists
+        _traitKeys.add(traitKey);
+
+        _traits[tokenId][traitKey] = newValue;
+
+        emit TraitUpdated(traitKey, tokenId, newValue);
+    }
+
+    /**
+     * @notice Set the URI for the trait metadata
+     * @param uri The new URI to set
+     */
+    function _setTraitMetadataURI(string calldata uri) internal virtual {
+        _traitMetadataURI = uri;
+        emit TraitMetadataURIUpdated();
+    }
+
+    function supportsInterface(bytes4 interfaceId) public view virtual returns (bool) {
+        return interfaceId == type(IERC7496).interfaceId;
+    }
+}