Gas token integration

contracts/interfaces/IGasToken.sol

@@ -0,0 +1,9 @@
+pragma solidity 0.4.24;
+
+interface IGasToken {
+    function balanceOf(address owner) external view returns (uint256);
+    function transfer(address to, uint256 value) external returns (bool);
+    function transferFrom(address from, address to, uint256 value) external returns (bool);
+    function allowance(address owner, address spender) external view returns (uint256);
+    function mint(uint256 value) external;
+}

contracts/mocks/ForeignAMBWithGasTokenMock.sol

@@ -0,0 +1,18 @@
+pragma solidity 0.4.24;
+
+import "../upgradeable_contracts/arbitrary_message/ForeignAMBWithGasToken.sol";
+
+/**
+* @title ForeignAMBWithGasTokenMock
+* @dev Wrapper on ForeignAMB contract, which supports minting gas tokens while passing messages
+*/
+contract ForeignAMBWithGasTokenMock is ForeignAMBWithGasToken {
+    function gasToken() public pure returns (IGasToken) {
+        // Address generated in unit test, also hardcoded in GasTokenMock
+        return IGasToken(0xEC8bE1A5630364292E56D01129E8ee8A9578d7D8);
+    }
+
+    function collectGasTokens() external {
+        _collectGasTokens();
+    }
+}

contracts/mocks/GasTokenMock.sol

@@ -0,0 +1,329 @@
+//solhint-disable
+pragma solidity ^0.4.24;
+
+contract Rlp {
+    uint256 constant ADDRESS_BYTES = 20;
+    uint256 constant MAX_SINGLE_BYTE = 128;
+    uint256 constant MAX_NONCE = 256**9 - 1;
+
+    // count number of bytes required to represent an unsigned integer
+    function count_bytes(uint256 n) pure internal returns (uint256 c) {
+        uint i = 0;
+        uint mask = 1;
+        while (n >= mask) {
+            i += 1;
+            mask *= 256;
+        }
+
+        return i;
+    }
+
+    function mk_contract_address(address a, uint256 n) pure internal returns (address rlp) {
+        /*
+         * make sure the RLP encoding fits in one word:
+         * total_length      1 byte
+         * address_length    1 byte
+         * address          20 bytes
+         * nonce_length      1 byte (or 0)
+         * nonce           1-9 bytes
+         *                ==========
+         *                24-32 bytes
+         */
+        require(n <= MAX_NONCE);
+
+        // number of bytes required to write down the nonce
+        uint256 nonce_bytes;
+        // length in bytes of the RLP encoding of the nonce
+        uint256 nonce_rlp_len;
+
+        if (0 < n && n < MAX_SINGLE_BYTE) {
+            // nonce fits in a single byte
+            // RLP(nonce) = nonce
+            nonce_bytes = 1;
+            nonce_rlp_len = 1;
+        } else {
+            // RLP(nonce) = [num_bytes_in_nonce nonce]
+            nonce_bytes = count_bytes(n);
+            nonce_rlp_len = nonce_bytes + 1;
+        }
+
+        // [address_length(1) address(20) nonce_length(0 or 1) nonce(1-9)]
+        uint256 tot_bytes = 1 + ADDRESS_BYTES + nonce_rlp_len;
+
+        // concatenate all parts of the RLP encoding in the leading bytes of
+        // one 32-byte word
+        uint256 word = ((192 + tot_bytes) * 256**31) +
+                       ((128 + ADDRESS_BYTES) * 256**30) +
+                       (uint256(a) * 256**10);
+
+        if (0 < n && n < MAX_SINGLE_BYTE) {
+            word += n * 256**9;
+        } else {
+            word += (128 + nonce_bytes) * 256**9;
+            word += n * 256**(9 - nonce_bytes);
+        }
+
+        uint256 hash;
+
+        assembly {
+            let mem_start := mload(0x40)        // get a pointer to free memory
+            mstore(mem_start, word)             // store the rlp encoding
+            hash := sha3(mem_start,
+                         add(tot_bytes, 1))     // hash the rlp encoding
+        }
+
+        // interpret hash as address (20 least significant bytes)
+        return address(hash);
+    }
+}
+
+contract GasTokenMock is Rlp {
+    //////////////////////////////////////////////////////////////////////////
+    // Generic ERC20
+    //////////////////////////////////////////////////////////////////////////
+
+    // owner -> amount
+    mapping(address => uint256) s_balances;
+    // owner -> spender -> max amount
+    mapping(address => mapping(address => uint256)) s_allowances;
+
+    event Transfer(address indexed from, address indexed to, uint256 value);
+
+    event Approval(address indexed owner, address indexed spender, uint256 value);
+
+    // Spec: Get the account balance of another account with address `owner`
+    function balanceOf(address owner) public constant returns (uint256 balance) {
+        return s_balances[owner];
+    }
+
+    function internalTransfer(address from, address to, uint256 value) internal returns (bool success) {
+        if (value <= s_balances[from]) {
+            s_balances[from] -= value;
+            s_balances[to] += value;
+            Transfer(from, to, value);
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    // Spec: Send `value` amount of tokens to address `to`
+    function transfer(address to, uint256 value) public returns (bool success) {
+        address from = msg.sender;
+        return internalTransfer(from, to, value);
+    }
+
+    // Spec: Send `value` amount of tokens from address `from` to address `to`
+    function transferFrom(address from, address to, uint256 value) public returns (bool success) {
+        address spender = msg.sender;
+        if(value <= s_allowances[from][spender] && internalTransfer(from, to, value)) {
+            s_allowances[from][spender] -= value;
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    // Spec: Allow `spender` to withdraw from your account, multiple times, up
+    // to the `value` amount. If this function is called again it overwrites the
+    // current allowance with `value`.
+    function approve(address spender, uint256 value) public returns (bool success) {
+        address owner = msg.sender;
+        if (value != 0 && s_allowances[owner][spender] != 0) {
+            return false;
+        }
+        s_allowances[owner][spender] = value;
+        Approval(owner, spender, value);
+        return true;
+    }
+
+    // Spec: Returns the `amount` which `spender` is still allowed to withdraw
+    // from `owner`.
+    // What if the allowance is higher than the balance of the `owner`?
+    // Callers should be careful to use min(allowance, balanceOf) to make sure
+    // that the allowance is actually present in the account!
+    function allowance(address owner, address spender) public constant returns (uint256 remaining) {
+        return s_allowances[owner][spender];
+    }
+
+    //////////////////////////////////////////////////////////////////////////
+    // GasToken specifics
+    //////////////////////////////////////////////////////////////////////////
+
+    uint8 constant public decimals = 2;
+    string constant public name = "Gastoken.io";
+    string constant public symbol = "GST2";
+
+    // We build a queue of nonces at which child contracts are stored. s_head is
+    // the nonce at the head of the queue, s_tail is the nonce behind the tail
+    // of the queue. The queue grows at the head and shrinks from the tail.
+    // Note that when and only when a contract CREATEs another contract, the
+    // creating contract's nonce is incremented.
+    // The first child contract is created with nonce == 1, the second child
+    // contract is created with nonce == 2, and so on...
+    // For example, if there are child contracts at nonces [2,3,4],
+    // then s_head == 4 and s_tail == 1. If there are no child contracts,
+    // s_head == s_tail.
+    uint256 s_head;
+    uint256 s_tail;
+
+    // totalSupply gives  the number of tokens currently in existence
+    // Each token corresponds to one child contract that can be SELFDESTRUCTed
+    // for a gas refund.
+    function totalSupply() public constant returns (uint256 supply) {
+        return s_head - s_tail;
+    }
+
+    // Creates a child contract that can only be destroyed by this contract.
+    function makeChild() internal returns (address addr) {
+        assembly {
+            // EVM assembler of runtime portion of child contract:
+            //     ;; Pseudocode: if (msg.sender != 0x0000000000b3f879cb30fe243b4dfee438691c04) { throw; }
+            //     ;;             suicide(msg.sender)
+            //     PUSH15 0xb3f879cb30fe243b4dfee438691c04 ;; hardcoded address of this contract
+            //     CALLER
+            //     XOR
+            //     PC
+            //     JUMPI
+            //     CALLER
+            //     SELFDESTRUCT
+            // Or in binary: 6eb3f879cb30fe243b4dfee438691c043318585733ff
+            // Since the binary is so short (22 bytes), we can get away
+            // with a very simple initcode:
+            //     PUSH22 0x6eb3f879cb30fe243b4dfee438691c043318585733ff
+            //     PUSH1 0
+            //     MSTORE ;; at this point, memory locations mem[10] through
+            //            ;; mem[31] contain the runtime portion of the child
+            //            ;; contract. all that's left to do is to RETURN this
+            //            ;; chunk of memory.
+            //     PUSH1 22 ;; length
+            //     PUSH1 10 ;; offset
+            //     RETURN
+            // Or in binary: 756eb3f879cb30fe243b4dfee438691c043318585733ff6000526016600af3
+            // Almost done! All we have to do is put this short (31 bytes) blob into
+            // memory and call CREATE with the appropriate offsets.
+            let solidity_free_mem_ptr := mload(0x40)
+            // replaced XOR by LT in this mock
+            mstore(solidity_free_mem_ptr, 0x00756eb3f879cb30fe243b4dfee438691c043310585733ff6000526016600af3)
+            addr := create(0, add(solidity_free_mem_ptr, 1), 31)
+        }
+    }
+
+    // Mints `value` new sub-tokens (e.g. cents, pennies, ...) by creating `value`
+    // new child contracts. The minted tokens are owned by the caller of this
+    // function.
+    function mint(uint256 value) public {
+        for (uint256 i = 0; i < value; i++) {
+            makeChild();
+        }
+        s_head += value;
+        s_balances[msg.sender] += value;
+    }
+
+    // Destroys `value` child contracts and updates s_tail.
+    //
+    // This function is affected by an issue in solc: https://github.com/ethereum/solidity/issues/2999
+    // The `mk_contract_address(this, i).call();` doesn't forward all available gas, but only GAS - 25710.
+    // As a result, when this line is executed with e.g. 30000 gas, the callee will have less than 5000 gas
+    // available and its SELFDESTRUCT operation will fail leading to no gas refund occurring.
+    // The remaining ~29000 gas left after the call is enough to update s_tail and the caller's balance.
+    // Hence tokens will have been destroyed without a commensurate gas refund.
+    // Fortunately, there is a simple workaround:
+    // Whenever you call free, freeUpTo, freeFrom, or freeUpToFrom, ensure that you pass at least
+    // 25710 + `value` * (1148 + 5722 + 150) gas. (It won't all be used)
+    function destroyChildren(uint256 value) internal {
+        uint256 tail = s_tail;
+        // tail points to slot behind the last contract in the queue
+        for (uint256 i = tail + 1; i <= tail + value; i++) {
+            mk_contract_address(this, i).call();
+        }
+
+        s_tail = tail + value;
+    }
+
+    // Frees `value` sub-tokens (e.g. cents, pennies, ...) belonging to the
+    // caller of this function by destroying `value` child contracts, which
+    // will trigger a partial gas refund.
+    // You should ensure that you pass at least 25710 + `value` * (1148 + 5722 + 150) gas
+    // when calling this function. For details, see the comment above `destroyChildren`.
+    function free(uint256 value) public returns (bool success) {
+        uint256 from_balance = s_balances[msg.sender];
+        if (value > from_balance) {
+            return false;
+        }
+
+        destroyChildren(value);
+
+        s_balances[msg.sender] = from_balance - value;
+
+        return true;
+    }
+
+    // Frees up to `value` sub-tokens. Returns how many tokens were freed.
+    // Otherwise, identical to free.
+    // You should ensure that you pass at least 25710 + `value` * (1148 + 5722 + 150) gas
+    // when calling this function. For details, see the comment above `destroyChildren`.
+    function freeUpTo(uint256 value) public returns (uint256 freed) {
+        uint256 from_balance = s_balances[msg.sender];
+        if (value > from_balance) {
+            value = from_balance;
+        }
+
+        destroyChildren(value);
+
+        s_balances[msg.sender] = from_balance - value;
+
+        return value;
+    }
+
+    // Frees `value` sub-tokens owned by address `from`. Requires that `msg.sender`
+    // has been approved by `from`.
+    // You should ensure that you pass at least 25710 + `value` * (1148 + 5722 + 150) gas
+    // when calling this function. For details, see the comment above `destroyChildren`.
+    function freeFrom(address from, uint256 value) public returns (bool success) {
+        address spender = msg.sender;
+        uint256 from_balance = s_balances[from];
+        if (value > from_balance) {
+            return false;
+        }
+
+        mapping(address => uint256) from_allowances = s_allowances[from];
+        uint256 spender_allowance = from_allowances[spender];
+        if (value > spender_allowance) {
+            return false;
+        }
+
+        destroyChildren(value);
+
+        s_balances[from] = from_balance - value;
+        from_allowances[spender] = spender_allowance - value;
+
+        return true;
+    }
+
+    // Frees up to `value` sub-tokens owned by address `from`. Returns how many tokens were freed.
+    // Otherwise, identical to `freeFrom`.
+    // You should ensure that you pass at least 25710 + `value` * (1148 + 5722 + 150) gas
+    // when calling this function. For details, see the comment above `destroyChildren`.
+    function freeFromUpTo(address from, uint256 value) public returns (uint256 freed) {
+        address spender = msg.sender;
+        uint256 from_balance = s_balances[from];
+        if (value > from_balance) {
+            value = from_balance;
+        }
+
+        mapping(address => uint256) from_allowances = s_allowances[from];
+        uint256 spender_allowance = from_allowances[spender];
+        if (value > spender_allowance) {
+            value = spender_allowance;
+        }
+
+        destroyChildren(value);
+
+        s_balances[from] = from_balance - value;
+        from_allowances[spender] = spender_allowance - value;
+
+        return value;
+    }
+}
+//solhint-enable