ERC721 full implementation (#803)

* Rename current ERC721 implementation to BaseERC721

* Implement ERC721 optional & approveAll functionality

* Support for new ERC721 interface

- Tests for new features are pending
- ERC721 is abstract, since it requires metadata implementation
- Move some methods into DeprecatedERC721 contract
- Reorganise base vs full implementation
- Pending tokenByIndex

* Add more tests for ERC721

* Implement suggestions by @dekz

* Update comments in ERC721 contracts

* Implement tokensByIndex extension

- Remove restrictions from mock mint and burn calls

* Add default implementation for metadata URI

This allows token implementation to be non-abstract

* Allow operators to call approve on a token

* Remove gas stipend restriction in call to 721 receiver

* Remove deprecated implementation

We only want to keep the interface, for interacting with already deployed contracts

* Add notice to isContract helper on constract constructors

* Change natspec delimiters for consistency

* Minor linting fixes

* Add constant modifier to ERC721_RECEIVED magic value

* Use 4-params safeTransferFrom for implementing the 3-params overload

* Minor text changes in natspec comments

* Use address(0) instead of 0 or 0x0

* Use if-statements instead of boolean one-liners for clarity

:-(

* Keep ownedTokensCount state var in sync in full ERC721 implementation

* Fix incorrect comparison when burning ERC721 tokens with metadata

* Use address(0) instead of 0 in one more place in ERC721

* Throw when querying balance for the zero address

Required by the spec

* Update links to approved version of EIP721

* Use explicit size for uint

* Remove unneeded internal function in ERC721

Also rename addToken and removeToken for added clarity

* Use underscore instead of 'do' prefix for internal methods in ERC721

* Fix failing test due to events reordering in ERC721 safe transfer

* Fix bug introduced in 74db03b

* Remove do prefix for internal setTokenUri method

* Allow transfers to self in ERC721

contracts/AddressUtils.sol

@@ -0,0 +1,21 @@
+pragma solidity ^0.4.18;
+
+/**
+ * Utility library of inline functions on addresses
+ */
+library AddressUtils {
+
+  /**
+   * Returns whether there is code in the target address
+   * @dev This function will return false if invoked during the constructor of a contract,
+   *  as the code is not actually created until after the constructor finishes.
+   * @param addr address address to check
+   * @return whether there is code in the target address
+   */
+  function isContract(address addr) internal view returns (bool) {
+    uint256 size;
+    assembly { size := extcodesize(addr) }
+    return size > 0;
+  }
+
+}

contracts/mocks/ERC721BasicTokenMock.sol

@@ -0,0 +1,17 @@
+pragma solidity ^0.4.18;
+
+import "../token/ERC721/ERC721BasicToken.sol";
+
+/**
+ * @title ERC721BasicTokenMock
+ * This mock just provides a public mint and burn functions for testing purposes
+ */
+contract ERC721BasicTokenMock is ERC721BasicToken {
+  function mint(address _to, uint256 _tokenId) public {
+    super._mint(_to, _tokenId);
+  }
+
+  function burn(uint256 _tokenId) public {
+    super._burn(ownerOf(_tokenId), _tokenId);
+  }
+}

contracts/mocks/ERC721ReceiverMock.sol

@@ -0,0 +1,21 @@
+pragma solidity ^0.4.18;
+
+import "../token/ERC721/ERC721Receiver.sol";
+
+contract ERC721ReceiverMock is ERC721Receiver {
+  bytes4 retval;
+  bool reverts;
+
+  event Received(address _address, uint256 _tokenId, bytes _data, uint256 _gas);
+
+  function ERC721ReceiverMock(bytes4 _retval, bool _reverts) public {
+    retval = _retval;
+    reverts = _reverts;
+  }
+
+  function onERC721Received(address _address, uint256 _tokenId, bytes _data) public returns(bytes4) {
+    require(!reverts);
+    Received(_address, _tokenId, _data, msg.gas);
+    return retval;
+  }
+}

contracts/mocks/ERC721TokenMock.sol

@@ -4,16 +4,23 @@ import "../token/ERC721/ERC721Token.sol";
 
 /**
  * @title ERC721TokenMock
- * This mock just provides a public mint and burn functions for testing purposes.
+ * This mock just provides a public mint and burn functions for testing purposes,
+ * and a public setter for metadata URI
  */
 contract ERC721TokenMock is ERC721Token {
-  function ERC721TokenMock() ERC721Token() public { }
+  function ERC721TokenMock(string name, string symbol) public
+    ERC721Token(name, symbol)
+  { }
 
   function mint(address _to, uint256 _tokenId) public {
     super._mint(_to, _tokenId);
   }
 
   function burn(uint256 _tokenId) public {
-    super._burn(_tokenId);
+    super._burn(ownerOf(_tokenId), _tokenId);
   }
-}
+
+  function setTokenURI(uint256 _tokenId, string _uri) public {
+    super._setTokenURI(_tokenId, _uri);
+  }
+}

contracts/token/ERC721/DeprecatedERC721.sol

@@ -0,0 +1,15 @@
+pragma solidity ^0.4.18;
+
+import "./ERC721.sol";
+
+/**
+ * @title ERC-721 methods shipped in OpenZeppelin v1.7.0, removed in the latest version of the standard
+ * @dev Only use this interface for compatibility with previously deployed contracts
+ * @dev Use ERC721 for interacting with new contracts which are standard-compliant
+ */
+contract DeprecatedERC721 is ERC721 {
+  function takeOwnership(uint256 _tokenId) public;
+  function transfer(address _to, uint256 _tokenId) public;
+  function tokensOf(address _owner) public view returns (uint256[]);
+}
+

contracts/token/ERC721/ERC721.sol

@@ -1,16 +1,30 @@
 pragma solidity ^0.4.18;
 
+import "./ERC721Basic.sol";
+
+/**
+ * @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
+ * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
+ */
+contract ERC721Enumerable is ERC721Basic {
+  function totalSupply() public view returns (uint256);
+  function tokenOfOwnerByIndex(address _owner, uint256 _index) public view returns (uint256 _tokenId);
+  function tokenByIndex(uint256 _index) public view returns (uint256);
+}
+
 /**
- * @title ERC721 interface
- * @dev see https://github.com/ethereum/eips/issues/721
+ * @title ERC-721 Non-Fungible Token Standard, optional metadata extension
+ * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
  */
-contract ERC721 {
-  event Transfer(address indexed _from, address indexed _to, uint256 _tokenId);
-  event Approval(address indexed _owner, address indexed _approved, uint256 _tokenId);
+contract ERC721Metadata is ERC721Basic {
+  function name() public view returns (string _name);
+  function symbol() public view returns (string _symbol);
+  function tokenURI(uint256 _tokenId) public view returns (string);
+}
 
-  function balanceOf(address _owner) public view returns (uint256 _balance);
-  function ownerOf(uint256 _tokenId) public view returns (address _owner);
-  function transfer(address _to, uint256 _tokenId) public;
-  function approve(address _to, uint256 _tokenId) public;
-  function takeOwnership(uint256 _tokenId) public;
+/**
+ * @title ERC-721 Non-Fungible Token Standard, full implementation interface
+ * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
+ */
+contract ERC721 is ERC721Basic, ERC721Enumerable, ERC721Metadata {
 }

contracts/token/ERC721/ERC721Basic.sol

@@ -0,0 +1,25 @@
+pragma solidity ^0.4.18;
+
+/**
+ * @title ERC721 Non-Fungible Token Standard basic interface
+ * @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
+ */
+contract ERC721Basic {
+  event Transfer(address indexed _from, address indexed _to, uint256 _tokenId);
+  event Approval(address indexed _owner, address indexed _approved, uint256 _tokenId);
+  event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved);  
+
+  function balanceOf(address _owner) public view returns (uint256 _balance);
+  function ownerOf(uint256 _tokenId) public view returns (address _owner);
+  function exists(uint256 _tokenId) public view returns (bool _exists);
+
+  function approve(address _to, uint256 _tokenId) public;
+  function getApproved(uint256 _tokenId) public view returns (address _operator);
+
+  function setApprovalForAll(address _operator, bool _approved) public;
+  function isApprovedForAll(address _owner, address _operator) public view returns (bool);
+
+  function transferFrom(address _from, address _to, uint256 _tokenId) public;
+  function safeTransferFrom(address _from, address _to, uint256 _tokenId) public;  
+  function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes _data) public;
+}