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The Pausable contract provides an emergency stop mechanism that allows authorized pausers to halt contract operations when necessary. This is a critical security feature for responding to vulnerabilities or attacks. Contract: src/roles/Pausable.sol

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Key Concepts

  • Paused State: Boolean flag indicating whether the contract is paused
  • Pauser Role: Authorized address that can pause and unpause the contract
  • whenNotPaused Modifier: Guards functions to prevent execution when paused

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State Variables

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paused

bool public paused = false
Indicates whether the contract is currently paused. When true, functions with the whenNotPaused modifier cannot be executed. Default: false

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Functions

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pause

function pause() external onlyPauser
Pauses the contract, preventing execution of functions protected by the whenNotPaused modifier. Requirements:
  • Caller must be the pauser
Effects:
  • Sets paused to true
Emits: Pause() Source: Pausable.sol:64

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unpause

function unpause() external onlyPauser
Unpauses the contract, restoring normal operation. Requirements:
  • Caller must be the pauser
Effects:
  • Sets paused to false
Emits: Unpause() Source: Pausable.sol:72

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updatePauser

function updatePauser(address _newPauser) external onlyOwner
Updates the pauser role to a new address. Parameters:
  • _newPauser: Address of the new pauser
Requirements:
  • Caller must be the owner
  • New pauser must be non-zero address
Emits: PauserChanged(address indexed newAddress) Source: Pausable.sol:80

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pauser

function pauser() external view returns (address)
Returns the current pauser address. Returns: Address of the current pauser Source: Pausable.sol:57

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Modifiers

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whenNotPaused

modifier whenNotPaused()
Restricts function execution to when the contract is not paused. Reverts: “Pausable: paused” if the contract is currently paused Usage: Apply to functions that should be disabled during emergency pause Source: Pausable.sol:40 Example: 
function depositForBurn(
    uint256 amount,
    uint32 destinationDomain,
    bytes32 mintRecipient,
    address burnToken
) external whenNotPaused {
    // Function logic
}

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onlyPauser

modifier onlyPauser()
Restricts function access to the pauser only. Reverts: “Pausable: caller is not the pauser” if caller is not the pauser Source: Pausable.sol:48

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Events

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Pause

event Pause()
Emitted when the contract is paused.

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Unpause

event Unpause()
Emitted when the contract is unpaused.

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PauserChanged

event PauserChanged(address indexed newAddress)
Emitted when the pauser role is transferred to a new address. Parameters:
  • newAddress: Address of the new pauser

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Internal Functions

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_updatePauser

function _updatePauser(address _newPauser) internal
Internal function to update the pauser role. Parameters:
  • _newPauser: Address of the new pauser
Requirements:
  • New pauser must be non-zero address
Emits: PauserChanged(address indexed newAddress) Source: Pausable.sol:87

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Usage Example

// Pause the contract in case of emergency (as pauser)
pausable.pause();

// Check if contract is paused
bool isPaused = pausable.paused();

// Unpause after issue is resolved
pausable.unpause();

// Transfer pauser role (as owner)
pausable.updatePauser(0x123...);

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Integration with CCTP

In CCTP contracts, the whenNotPaused modifier is applied to critical functions:
  • TokenMessenger: depositForBurn(), depositForBurnWithCaller(), replaceDepositForBurn()
  • MessageTransmitter: receiveMessage(), replaceMessage()
When paused, these operations are disabled while administrative functions remain accessible.

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Security Considerations

  • The pauser role is separate from the owner role for operational flexibility
  • Only the owner can change the pauser address
  • Pausing is immediate and affects all protected functions
  • The pauser should be a trusted address (e.g., multisig or DAO)
  • Consider implementing monitoring to detect when pause is triggered
  • Ensure the pauser key is highly secure and accessible during emergencies

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Origin

Forked from Centre USDC Pausable with modifications:
  • Updated Solidity version from 0.6.12 to 0.7.6
  • Changed pauser visibility to private with external getter
  • Added internal _updatePauser function

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