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Overview

The Optimism_SpokePool is deployed on Optimism mainnet. It extends the Ovm_SpokePool base contract and adds custom bridging logic for Synthetix-related assets like SNX, which use a specialized bridge instead of the standard OP Stack bridge. Contract: contracts/Optimism_SpokePool.sol

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Key Characteristics

  • Extends Ovm_SpokePool: Inherits OP Stack cross-domain messaging and standard bridge logic
  • Custom SNX bridge: Implements special handling for Synthetix Network Token (SNX)
  • CCTP support: Inherits Circle CCTP integration from Ovm_SpokePool
  • Standard OP Stack patterns: Uses CrossDomainMessenger for admin verification

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Inheritance

contract Optimism_SpokePool is Ovm_SpokePool
  • Inherits Ovm_SpokePool which provides OP Stack bridging functionality
  • Inherits CircleCCTPAdapter through Ovm_SpokePool for USDC bridging

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Constructor

constructor(
    address _wrappedNativeTokenAddress,
    uint32 _depositQuoteTimeBuffer,
    uint32 _fillDeadlineBuffer,
    IERC20 _l2Usdc,
    ITokenMessenger _cctpTokenMessenger
)
    Ovm_SpokePool(
        _wrappedNativeTokenAddress,
        _depositQuoteTimeBuffer,
        _fillDeadlineBuffer,
        _l2Usdc,
        _cctpTokenMessenger
    )
Parameters:
  • _wrappedNativeTokenAddress: Address of WETH on Optimism
  • _depositQuoteTimeBuffer: Max age for deposit quote timestamps
  • _fillDeadlineBuffer: Max future offset for fill deadlines
  • _l2Usdc: Circle USDC address on Optimism (or 0x0 to disable CCTP)
  • _cctpTokenMessenger: Circle TokenMessenger contract for CCTP bridging

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Initialization

function initialize(
    uint32 _initialDepositId,
    address _crossDomainAdmin,
    address _withdrawalRecipient
) public initializer
Parameters:
  • _initialDepositId: Starting deposit nonce
  • _crossDomainAdmin: L1 HubPool address
  • _withdrawalRecipient: Address receiving bridged tokens on L1 (typically HubPool)
Implementation: 
__OvmSpokePool_init(
    _initialDepositId,
    _crossDomainAdmin,
    _withdrawalRecipient,
    Lib_PredeployAddresses.OVM_ETH
);
Sets l2Eth to Optimism’s predeploy ETH address (0xDeadDeAddeAddEAddeadDEaDDEAdDeaDDeAD0000).

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Admin Verification

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_requireAdminSender()

Inherited from Ovm_SpokePool: 
function _requireAdminSender() internal view override {
    if (LibOptimismUpgradeable.crossChainSender(MESSENGER) != crossDomainAdmin)
        revert NotCrossDomainAdmin();
}
OP Stack verification:
  • Checks that the cross-chain message sender (via L2CrossDomainMessenger) is the HubPool
  • Uses Optimism’s CrossDomainMessenger contract at predeploy address
  • MESSENGER constant: 0x4200000000000000000000000000000000000007

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Token Bridging

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_bridgeTokensToHubPool()

function _bridgeTokensToHubPool(
    uint256 amountToReturn,
    address l2TokenAddress
) internal virtual override {
    // Handle custom SNX bridge which doesn't conform to the standard bridge interface
    if (l2TokenAddress == SNX)
        SynthetixBridgeToBase(SYNTHETIX_BRIDGE).withdrawTo(
            withdrawalRecipient, // _to
            amountToReturn       // _amount
        );
    else
        super._bridgeTokensToHubPool(amountToReturn, l2TokenAddress);
}
Bridging logic:
  1. SNX tokens: Use Synthetix’s custom bridge
    • Bridge address: 0x136b1EC699c62b0606854056f02dC7Bb80482d63
    • SNX address: 0x8700dAec35aF8Ff88c16BdF0418774CB3D7599B4
    • Calls withdrawTo() directly on SynthetixBridgeToBase
  2. All other tokens: Delegate to parent Ovm_SpokePool._bridgeTokensToHubPool()
    • USDC via CCTP (if enabled)
    • WETH unwrapped to ETH then bridged via L2StandardBridge
    • Other ERC20s via L2StandardBridge or custom token bridges

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Synthetix Bridge Interface

interface SynthetixBridgeToBase {
    function withdrawTo(address to, uint256 amount) external;
}
Why SNX needs custom handling:
  • Synthetix uses a specialized bridge that predates the standard OP Stack bridge
  • The interface is non-standard (no L1 token parameter, different function signature)
  • SNX is a native L2 token on Optimism with different bridging requirements

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Contract Constants

// Address of custom bridge used to bridge Synthetix-related assets like SNX
address private constant SYNTHETIX_BRIDGE = 0x136b1EC699c62b0606854056f02dC7Bb80482d63;

// Address of SNX ERC20
address private constant SNX = 0x8700dAec35aF8Ff88c16BdF0418774CB3D7599B4;

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Inherited Features from Ovm_SpokePool

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Standard Bridge Integration

For non-SNX tokens, inherits from Ovm_SpokePool: 
// Standard token bridge
IL2ERC20Bridge(Lib_PredeployAddresses.L2_STANDARD_BRIDGE).withdrawTo(
    l2TokenAddress,
    withdrawalRecipient,
    amountToReturn,
    l1Gas,
    ""
);

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ETH/WETH Handling

// ETH is unwrapped from WETH before bridging
if (l2TokenAddress == address(wrappedNativeToken)) {
    WETH9Interface(l2TokenAddress).withdraw(amountToReturn);
    l2TokenAddress = l2Eth; // 0xDeadDeAddeAddEAddeadDEaDDEAdDeaDDeAD0000
    IL2ERC20Bridge(Lib_PredeployAddresses.L2_STANDARD_BRIDGE).withdrawTo{value: amountToReturn}(
        l2TokenAddress,
        withdrawalRecipient,
        amountToReturn,
        l1Gas,
        ""
    );
}

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CCTP USDC Bridging

// If CCTP is enabled and token is USDC
if (_isCCTPEnabled() && l2TokenAddress == address(usdcToken)) {
    _transferUsdc(withdrawalRecipient, amountToReturn);
}

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Custom Token Bridges

For tokens with custom bridges (e.g., DAI): 
mapping(address => address) public tokenBridges;
mapping(address => address) public remoteL1Tokens;

// Set via admin functions
function setTokenBridge(address l2Token, address tokenBridge) public onlyAdmin;
function setRemoteL1Token(address l2Token, address l1Token) public onlyAdmin;

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Pre-Execute Hook

function _preExecuteLeafHook(address l2TokenAddress) internal override {
    if (l2TokenAddress == address(wrappedNativeToken))
        _depositEthToWeth();
}
Wraps any ETH to WETH before executing relayer refunds or slow fills.

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Admin Functions (Inherited)

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setL1GasLimit()

function setL1GasLimit(uint32 newl1Gas) public onlyAdmin nonReentrant
Sets gas limit for L2→L1 messages.

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setTokenBridge()

function setTokenBridge(address l2Token, address tokenBridge) public onlyAdmin nonReentrant
Configures custom bridge for specific tokens.

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setRemoteL1Token()

function setRemoteL1Token(address l2Token, address l1Token) public onlyAdmin nonReentrant
Maps L2 native tokens to L1 addresses for bridgeERC20To() calls.

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Unique Features

  1. SNX-specific handling: Only major override from base Ovm_SpokePool
  2. Minimal additions: Most functionality inherited from Ovm_SpokePool
  3. Predeploy addresses: Uses Optimism’s standard predeploy contracts
  4. Virtual override: Allows further customization by child contracts (e.g., Base_SpokePool)

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Architecture Notes

  • Optimism_SpokePool is a thin wrapper around Ovm_SpokePool
  • The only custom logic is SNX bridge integration
  • Uses OP Stack’s CrossDomainMessenger for admin verification
  • Inherits multi-bridge support (CCTP, standard bridge, custom bridges)
  • The virtual keyword on _bridgeTokensToHubPool() allows chains like Base to further customize
  • SpokePool - Base contract
  • Optimism Adapter - L1→L2 message relay from HubPool
  • Ovm_SpokePool - Parent contract with OP Stack logic (see source code)