openzeppelin-contracts/docs/modules/api/pages/crosschain.adoc

:github-icon: pass:[<svg class="icon"><use href="#github-icon"/></svg>]
:CrossChainEnabled: pass:normal[xref:crosschain.adoc#CrossChainEnabled[`CrossChainEnabled`]]
:CrossChainEnabled: pass:normal[xref:crosschain.adoc#CrossChainEnabled[`CrossChainEnabled`]]
:CrossChainEnabled: pass:normal[xref:crosschain.adoc#CrossChainEnabled[`CrossChainEnabled`]]
:AccessControlCrossChain: pass:normal[xref:access.adoc#AccessControlCrossChain[`AccessControlCrossChain`]]
:CrossChainEnabled: pass:normal[xref:crosschain.adoc#CrossChainEnabled[`CrossChainEnabled`]]
:xref-CrossChainEnabledAMB-constructor-address-: xref:crosschain.adoc#CrossChainEnabledAMB-constructor-address-
:xref-CrossChainEnabledAMB-_isCrossChain--: xref:crosschain.adoc#CrossChainEnabledAMB-_isCrossChain--
:xref-CrossChainEnabledAMB-_crossChainSender--: xref:crosschain.adoc#CrossChainEnabledAMB-_crossChainSender--
:CrossChainEnabled-_isCrossChain: pass:normal[xref:crosschain.adoc#CrossChainEnabled-_isCrossChain--[`CrossChainEnabled._isCrossChain`]]
:CrossChainEnabled-_crossChainSender: pass:normal[xref:crosschain.adoc#CrossChainEnabled-_crossChainSender--[`CrossChainEnabled._crossChainSender`]]
:CrossChainEnabled: pass:normal[xref:crosschain.adoc#CrossChainEnabled[`CrossChainEnabled`]]
:CrossChainEnabledArbitrumL2: pass:normal[xref:crosschain.adoc#CrossChainEnabledArbitrumL2[`CrossChainEnabledArbitrumL2`]]
:xref-CrossChainEnabledArbitrumL1-constructor-address-: xref:crosschain.adoc#CrossChainEnabledArbitrumL1-constructor-address-
:xref-CrossChainEnabledArbitrumL1-_isCrossChain--: xref:crosschain.adoc#CrossChainEnabledArbitrumL1-_isCrossChain--
:xref-CrossChainEnabledArbitrumL1-_crossChainSender--: xref:crosschain.adoc#CrossChainEnabledArbitrumL1-_crossChainSender--
:CrossChainEnabled-_isCrossChain: pass:normal[xref:crosschain.adoc#CrossChainEnabled-_isCrossChain--[`CrossChainEnabled._isCrossChain`]]
:CrossChainEnabled-_crossChainSender: pass:normal[xref:crosschain.adoc#CrossChainEnabled-_crossChainSender--[`CrossChainEnabled._crossChainSender`]]
:CrossChainEnabled: pass:normal[xref:crosschain.adoc#CrossChainEnabled[`CrossChainEnabled`]]
:CrossChainEnabledArbitrumL1: pass:normal[xref:crosschain.adoc#CrossChainEnabledArbitrumL1[`CrossChainEnabledArbitrumL1`]]
:CrossChainEnabled: pass:normal[xref:crosschain.adoc#CrossChainEnabled[`CrossChainEnabled`]]
:xref-CrossChainEnabledArbitrumL2-_isCrossChain--: xref:crosschain.adoc#CrossChainEnabledArbitrumL2-_isCrossChain--
:xref-CrossChainEnabledArbitrumL2-_crossChainSender--: xref:crosschain.adoc#CrossChainEnabledArbitrumL2-_crossChainSender--
:CrossChainEnabled-_isCrossChain: pass:normal[xref:crosschain.adoc#CrossChainEnabled-_isCrossChain--[`CrossChainEnabled._isCrossChain`]]
:CrossChainEnabled-_crossChainSender: pass:normal[xref:crosschain.adoc#CrossChainEnabled-_crossChainSender--[`CrossChainEnabled._crossChainSender`]]
:CrossChainEnabled: pass:normal[xref:crosschain.adoc#CrossChainEnabled[`CrossChainEnabled`]]
:xref-CrossChainEnabledOptimism-constructor-address-: xref:crosschain.adoc#CrossChainEnabledOptimism-constructor-address-
:xref-CrossChainEnabledOptimism-_isCrossChain--: xref:crosschain.adoc#CrossChainEnabledOptimism-_isCrossChain--
:xref-CrossChainEnabledOptimism-_crossChainSender--: xref:crosschain.adoc#CrossChainEnabledOptimism-_crossChainSender--
:CrossChainEnabled-_isCrossChain: pass:normal[xref:crosschain.adoc#CrossChainEnabled-_isCrossChain--[`CrossChainEnabled._isCrossChain`]]
:CrossChainEnabled-_crossChainSender: pass:normal[xref:crosschain.adoc#CrossChainEnabled-_crossChainSender--[`CrossChainEnabled._crossChainSender`]]
:CrossChainEnabled: pass:normal[xref:crosschain.adoc#CrossChainEnabled[`CrossChainEnabled`]]
:xref-CrossChainEnabledPolygonChild-constructor-address-: xref:crosschain.adoc#CrossChainEnabledPolygonChild-constructor-address-
:xref-CrossChainEnabledPolygonChild-_isCrossChain--: xref:crosschain.adoc#CrossChainEnabledPolygonChild-_isCrossChain--
:xref-CrossChainEnabledPolygonChild-_crossChainSender--: xref:crosschain.adoc#CrossChainEnabledPolygonChild-_crossChainSender--
:xref-CrossChainEnabledPolygonChild-processMessageFromRoot-uint256-address-bytes-: xref:crosschain.adoc#CrossChainEnabledPolygonChild-processMessageFromRoot-uint256-address-bytes-
:xref-ReentrancyGuard-_reentrancyGuardEntered--: xref:security.adoc#ReentrancyGuard-_reentrancyGuardEntered--
:CrossChainEnabled-_isCrossChain: pass:normal[xref:crosschain.adoc#CrossChainEnabled-_isCrossChain--[`CrossChainEnabled._isCrossChain`]]
:CrossChainEnabled-_crossChainSender: pass:normal[xref:crosschain.adoc#CrossChainEnabled-_crossChainSender--[`CrossChainEnabled._crossChainSender`]]
:CrossChainEnabled: pass:normal[xref:crosschain.adoc#CrossChainEnabled[`CrossChainEnabled`]]
:xref-LibAMB-isCrossChain-address-: xref:crosschain.adoc#LibAMB-isCrossChain-address-
:xref-LibAMB-crossChainSender-address-: xref:crosschain.adoc#LibAMB-crossChainSender-address-
:LibArbitrumL2: pass:normal[xref:crosschain.adoc#LibArbitrumL2[`LibArbitrumL2`]]
:xref-LibArbitrumL1-isCrossChain-address-: xref:crosschain.adoc#LibArbitrumL1-isCrossChain-address-
:xref-LibArbitrumL1-crossChainSender-address-: xref:crosschain.adoc#LibArbitrumL1-crossChainSender-address-
:LibArbitrumL1: pass:normal[xref:crosschain.adoc#LibArbitrumL1[`LibArbitrumL1`]]
:xref-LibArbitrumL2-isCrossChain-address-: xref:crosschain.adoc#LibArbitrumL2-isCrossChain-address-
:xref-LibArbitrumL2-crossChainSender-address-: xref:crosschain.adoc#LibArbitrumL2-crossChainSender-address-
:xref-LibOptimism-isCrossChain-address-: xref:crosschain.adoc#LibOptimism-isCrossChain-address-
:xref-LibOptimism-crossChainSender-address-: xref:crosschain.adoc#LibOptimism-crossChainSender-address-
= Cross Chain Awareness

[.readme-notice]
NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/crosschain

This directory provides building blocks to improve cross-chain awareness of smart contracts.

- {CrossChainEnabled} is an abstraction that contains accessors and modifiers to control the execution flow when receiving cross-chain messages.

== CrossChainEnabled specializations

The following specializations of {CrossChainEnabled} provide implementations of the {CrossChainEnabled} abstraction for specific bridges. This can be used to complex cross-chain aware components such as {AccessControlCrossChain}.

:constructor: pass:normal[xref:#CrossChainEnabledAMB-constructor-address-[`++constructor++`]]
:_isCrossChain: pass:normal[xref:#CrossChainEnabledAMB-_isCrossChain--[`++_isCrossChain++`]]
:_crossChainSender: pass:normal[xref:#CrossChainEnabledAMB-_crossChainSender--[`++_crossChainSender++`]]

[.contract]
[[CrossChainEnabledAMB]]
=== `++CrossChainEnabledAMB++` link:https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.9.5/contracts/crosschain/amb/CrossChainEnabledAMB.sol[{github-icon},role=heading-link]

[.hljs-theme-light.nopadding]
```solidity
import "@openzeppelin/contracts/crosschain/amb/CrossChainEnabledAMB.sol";
```

https://docs.tokenbridge.net/amb-bridge/about-amb-bridge[AMB]
specialization or the {CrossChainEnabled} abstraction.

As of february 2020, AMB bridges are available between the following chains:

- https://docs.tokenbridge.net/eth-xdai-amb-bridge/about-the-eth-xdai-amb[ETH ⇌ xDai]
- https://docs.tokenbridge.net/eth-qdai-bridge/about-the-eth-qdai-amb[ETH ⇌ qDai]
- https://docs.tokenbridge.net/eth-etc-amb-bridge/about-the-eth-etc-amb[ETH ⇌ ETC]
- https://docs.tokenbridge.net/eth-bsc-amb/about-the-eth-bsc-amb[ETH ⇌ BSC]
- https://docs.tokenbridge.net/eth-poa-amb-bridge/about-the-eth-poa-amb[ETH ⇌ POA]
- https://docs.tokenbridge.net/bsc-xdai-amb/about-the-bsc-xdai-amb[BSC ⇌ xDai]
- https://docs.tokenbridge.net/poa-xdai-amb/about-the-poa-xdai-amb[POA ⇌ xDai]
- https://docs.tokenbridge.net/rinkeby-xdai-amb-bridge/about-the-rinkeby-xdai-amb[Rinkeby ⇌ xDai]
- https://docs.tokenbridge.net/kovan-sokol-amb-bridge/about-the-kovan-sokol-amb[Kovan ⇌ Sokol]

_Available since v4.6._

[.contract-index]
.Functions
--
* {xref-CrossChainEnabledAMB-constructor-address-}[`++constructor(bridge)++`]
* {xref-CrossChainEnabledAMB-_isCrossChain--}[`++_isCrossChain()++`]
* {xref-CrossChainEnabledAMB-_crossChainSender--}[`++_crossChainSender()++`]

[.contract-subindex-inherited]
.CrossChainEnabled

--

[.contract-item]
[[CrossChainEnabledAMB-constructor-address-]]
==== `[.contract-item-name]#++constructor++#++(address bridge)++` [.item-kind]#public#

[.contract-item]
[[CrossChainEnabledAMB-_isCrossChain--]]
==== `[.contract-item-name]#++_isCrossChain++#++() → bool++` [.item-kind]#internal#

see {CrossChainEnabled-_isCrossChain}

[.contract-item]
[[CrossChainEnabledAMB-_crossChainSender--]]
==== `[.contract-item-name]#++_crossChainSender++#++() → address++` [.item-kind]#internal#

see {CrossChainEnabled-_crossChainSender}

:constructor: pass:normal[xref:#CrossChainEnabledArbitrumL1-constructor-address-[`++constructor++`]]
:_isCrossChain: pass:normal[xref:#CrossChainEnabledArbitrumL1-_isCrossChain--[`++_isCrossChain++`]]
:_crossChainSender: pass:normal[xref:#CrossChainEnabledArbitrumL1-_crossChainSender--[`++_crossChainSender++`]]

[.contract]
[[CrossChainEnabledArbitrumL1]]
=== `++CrossChainEnabledArbitrumL1++` link:https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.9.5/contracts/crosschain/arbitrum/CrossChainEnabledArbitrumL1.sol[{github-icon},role=heading-link]

[.hljs-theme-light.nopadding]
```solidity
import "@openzeppelin/contracts/crosschain/arbitrum/CrossChainEnabledArbitrumL1.sol";
```

https://arbitrum.io/[Arbitrum] specialization or the
{CrossChainEnabled} abstraction the L1 side (mainnet).

This version should only be deployed on L1 to process cross-chain messages
originating from L2. For the other side, use {CrossChainEnabledArbitrumL2}.

The bridge contract is provided and maintained by the arbitrum team. You can
find the address of this contract on the rinkeby testnet in
https://developer.offchainlabs.com/docs/useful_addresses[Arbitrum's developer documentation].

_Available since v4.6._

[.contract-index]
.Functions
--
* {xref-CrossChainEnabledArbitrumL1-constructor-address-}[`++constructor(bridge)++`]
* {xref-CrossChainEnabledArbitrumL1-_isCrossChain--}[`++_isCrossChain()++`]
* {xref-CrossChainEnabledArbitrumL1-_crossChainSender--}[`++_crossChainSender()++`]

[.contract-subindex-inherited]
.CrossChainEnabled

--

[.contract-item]
[[CrossChainEnabledArbitrumL1-constructor-address-]]
==== `[.contract-item-name]#++constructor++#++(address bridge)++` [.item-kind]#internal#

[.contract-item]
[[CrossChainEnabledArbitrumL1-_isCrossChain--]]
==== `[.contract-item-name]#++_isCrossChain++#++() → bool++` [.item-kind]#internal#

see {CrossChainEnabled-_isCrossChain}

[.contract-item]
[[CrossChainEnabledArbitrumL1-_crossChainSender--]]
==== `[.contract-item-name]#++_crossChainSender++#++() → address++` [.item-kind]#internal#

see {CrossChainEnabled-_crossChainSender}

:_isCrossChain: pass:normal[xref:#CrossChainEnabledArbitrumL2-_isCrossChain--[`++_isCrossChain++`]]
:_crossChainSender: pass:normal[xref:#CrossChainEnabledArbitrumL2-_crossChainSender--[`++_crossChainSender++`]]

[.contract]
[[CrossChainEnabledArbitrumL2]]
=== `++CrossChainEnabledArbitrumL2++` link:https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.9.5/contracts/crosschain/arbitrum/CrossChainEnabledArbitrumL2.sol[{github-icon},role=heading-link]

[.hljs-theme-light.nopadding]
```solidity
import "@openzeppelin/contracts/crosschain/arbitrum/CrossChainEnabledArbitrumL2.sol";
```

https://arbitrum.io/[Arbitrum] specialization or the
{CrossChainEnabled} abstraction the L2 side (arbitrum).

This version should only be deployed on L2 to process cross-chain messages
originating from L1. For the other side, use {CrossChainEnabledArbitrumL1}.

Arbitrum L2 includes the `ArbSys` contract at a fixed address. Therefore,
this specialization of {CrossChainEnabled} does not include a constructor.

_Available since v4.6._

WARNING: There is currently a bug in Arbitrum that causes this contract to
fail to detect cross-chain calls when deployed behind a proxy. This will be
fixed when the network is upgraded to Arbitrum Nitro, currently scheduled for
August 31st 2022.

[.contract-index]
.Functions
--
* {xref-CrossChainEnabledArbitrumL2-_isCrossChain--}[`++_isCrossChain()++`]
* {xref-CrossChainEnabledArbitrumL2-_crossChainSender--}[`++_crossChainSender()++`]

[.contract-subindex-inherited]
.CrossChainEnabled

--

[.contract-item]
[[CrossChainEnabledArbitrumL2-_isCrossChain--]]
==== `[.contract-item-name]#++_isCrossChain++#++() → bool++` [.item-kind]#internal#

see {CrossChainEnabled-_isCrossChain}

[.contract-item]
[[CrossChainEnabledArbitrumL2-_crossChainSender--]]
==== `[.contract-item-name]#++_crossChainSender++#++() → address++` [.item-kind]#internal#

see {CrossChainEnabled-_crossChainSender}

:constructor: pass:normal[xref:#CrossChainEnabledOptimism-constructor-address-[`++constructor++`]]
:_isCrossChain: pass:normal[xref:#CrossChainEnabledOptimism-_isCrossChain--[`++_isCrossChain++`]]
:_crossChainSender: pass:normal[xref:#CrossChainEnabledOptimism-_crossChainSender--[`++_crossChainSender++`]]

[.contract]
[[CrossChainEnabledOptimism]]
=== `++CrossChainEnabledOptimism++` link:https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.9.5/contracts/crosschain/optimism/CrossChainEnabledOptimism.sol[{github-icon},role=heading-link]

[.hljs-theme-light.nopadding]
```solidity
import "@openzeppelin/contracts/crosschain/optimism/CrossChainEnabledOptimism.sol";
```

https://www.optimism.io/[Optimism] specialization or the
{CrossChainEnabled} abstraction.

The messenger (`CrossDomainMessenger`) contract is provided and maintained by
the optimism team. You can find the address of this contract on mainnet and
kovan in the https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts/deployments[deployments section of Optimism monorepo].

_Available since v4.6._

[.contract-index]
.Functions
--
* {xref-CrossChainEnabledOptimism-constructor-address-}[`++constructor(messenger)++`]
* {xref-CrossChainEnabledOptimism-_isCrossChain--}[`++_isCrossChain()++`]
* {xref-CrossChainEnabledOptimism-_crossChainSender--}[`++_crossChainSender()++`]

[.contract-subindex-inherited]
.CrossChainEnabled

--

[.contract-item]
[[CrossChainEnabledOptimism-constructor-address-]]
==== `[.contract-item-name]#++constructor++#++(address messenger)++` [.item-kind]#internal#

[.contract-item]
[[CrossChainEnabledOptimism-_isCrossChain--]]
==== `[.contract-item-name]#++_isCrossChain++#++() → bool++` [.item-kind]#internal#

see {CrossChainEnabled-_isCrossChain}

[.contract-item]
[[CrossChainEnabledOptimism-_crossChainSender--]]
==== `[.contract-item-name]#++_crossChainSender++#++() → address++` [.item-kind]#internal#

see {CrossChainEnabled-_crossChainSender}

:constructor: pass:normal[xref:#CrossChainEnabledPolygonChild-constructor-address-[`++constructor++`]]
:_isCrossChain: pass:normal[xref:#CrossChainEnabledPolygonChild-_isCrossChain--[`++_isCrossChain++`]]
:_crossChainSender: pass:normal[xref:#CrossChainEnabledPolygonChild-_crossChainSender--[`++_crossChainSender++`]]
:processMessageFromRoot: pass:normal[xref:#CrossChainEnabledPolygonChild-processMessageFromRoot-uint256-address-bytes-[`++processMessageFromRoot++`]]

[.contract]
[[CrossChainEnabledPolygonChild]]
=== `++CrossChainEnabledPolygonChild++` link:https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.9.5/contracts/crosschain/polygon/CrossChainEnabledPolygonChild.sol[{github-icon},role=heading-link]

[.hljs-theme-light.nopadding]
```solidity
import "@openzeppelin/contracts/crosschain/polygon/CrossChainEnabledPolygonChild.sol";
```

https://polygon.technology/[Polygon] specialization or the
{CrossChainEnabled} abstraction the child side (polygon/mumbai).

This version should only be deployed on child chain to process cross-chain
messages originating from the parent chain.

The fxChild contract is provided and maintained by the polygon team. You can
find the address of this contract polygon and mumbai in
https://docs.polygon.technology/docs/develop/l1-l2-communication/fx-portal/#contract-addresses[Polygon's Fx-Portal documentation].

_Available since v4.6._

[.contract-index]
.Functions
--
* {xref-CrossChainEnabledPolygonChild-constructor-address-}[`++constructor(fxChild)++`]
* {xref-CrossChainEnabledPolygonChild-_isCrossChain--}[`++_isCrossChain()++`]
* {xref-CrossChainEnabledPolygonChild-_crossChainSender--}[`++_crossChainSender()++`]
* {xref-CrossChainEnabledPolygonChild-processMessageFromRoot-uint256-address-bytes-}[`++processMessageFromRoot(, rootMessageSender, data)++`]

[.contract-subindex-inherited]
.ReentrancyGuard
* {xref-ReentrancyGuard-_reentrancyGuardEntered--}[`++_reentrancyGuardEntered()++`]

[.contract-subindex-inherited]
.CrossChainEnabled

[.contract-subindex-inherited]
.IFxMessageProcessor

--

[.contract-item]
[[CrossChainEnabledPolygonChild-constructor-address-]]
==== `[.contract-item-name]#++constructor++#++(address fxChild)++` [.item-kind]#internal#

[.contract-item]
[[CrossChainEnabledPolygonChild-_isCrossChain--]]
==== `[.contract-item-name]#++_isCrossChain++#++() → bool++` [.item-kind]#internal#

see {CrossChainEnabled-_isCrossChain}

[.contract-item]
[[CrossChainEnabledPolygonChild-_crossChainSender--]]
==== `[.contract-item-name]#++_crossChainSender++#++() → address++` [.item-kind]#internal#

see {CrossChainEnabled-_crossChainSender}

[.contract-item]
[[CrossChainEnabledPolygonChild-processMessageFromRoot-uint256-address-bytes-]]
==== `[.contract-item-name]#++processMessageFromRoot++#++(uint256, address rootMessageSender, bytes data)++` [.item-kind]#external#

External entry point to receive and relay messages originating
from the fxChild.

Non-reentrancy is crucial to avoid a cross-chain call being able
to impersonate anyone by just looping through this with user-defined
arguments.

Note: if _fxChild calls any other function that does a delegate-call,
then security could be compromised.

== Libraries for cross-chain

In addition to the {CrossChainEnabled} abstraction, cross-chain awareness is also available through libraries. These libraries can be used to build complex designs such as contracts with the ability to interact with multiple bridges.

:isCrossChain: pass:normal[xref:#LibAMB-isCrossChain-address-[`++isCrossChain++`]]
:crossChainSender: pass:normal[xref:#LibAMB-crossChainSender-address-[`++crossChainSender++`]]

[.contract]
[[LibAMB]]
=== `++LibAMB++` link:https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.9.5/contracts/crosschain/amb/LibAMB.sol[{github-icon},role=heading-link]

[.hljs-theme-light.nopadding]
```solidity
import "@openzeppelin/contracts/crosschain/amb/LibAMB.sol";
```

Primitives for cross-chain aware contracts using the
https://docs.tokenbridge.net/amb-bridge/about-amb-bridge[AMB]
family of bridges.

[.contract-index]
.Functions
--
* {xref-LibAMB-isCrossChain-address-}[`++isCrossChain(bridge)++`]
* {xref-LibAMB-crossChainSender-address-}[`++crossChainSender(bridge)++`]

--

[.contract-item]
[[LibAMB-isCrossChain-address-]]
==== `[.contract-item-name]#++isCrossChain++#++(address bridge) → bool++` [.item-kind]#internal#

Returns whether the current function call is the result of a
cross-chain message relayed by `bridge`.

[.contract-item]
[[LibAMB-crossChainSender-address-]]
==== `[.contract-item-name]#++crossChainSender++#++(address bridge) → address++` [.item-kind]#internal#

Returns the address of the sender that triggered the current
cross-chain message through `bridge`.

NOTE: {isCrossChain} should be checked before trying to recover the
sender, as it will revert with `NotCrossChainCall` if the current
function call is not the result of a cross-chain message.

:isCrossChain: pass:normal[xref:#LibArbitrumL1-isCrossChain-address-[`++isCrossChain++`]]
:crossChainSender: pass:normal[xref:#LibArbitrumL1-crossChainSender-address-[`++crossChainSender++`]]

[.contract]
[[LibArbitrumL1]]
=== `++LibArbitrumL1++` link:https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.9.5/contracts/crosschain/arbitrum/LibArbitrumL1.sol[{github-icon},role=heading-link]

[.hljs-theme-light.nopadding]
```solidity
import "@openzeppelin/contracts/crosschain/arbitrum/LibArbitrumL1.sol";
```

Primitives for cross-chain aware contracts for
https://arbitrum.io/[Arbitrum].

This version should only be used on L1 to process cross-chain messages
originating from L2. For the other side, use {LibArbitrumL2}.

[.contract-index]
.Functions
--
* {xref-LibArbitrumL1-isCrossChain-address-}[`++isCrossChain(bridge)++`]
* {xref-LibArbitrumL1-crossChainSender-address-}[`++crossChainSender(bridge)++`]

--

[.contract-item]
[[LibArbitrumL1-isCrossChain-address-]]
==== `[.contract-item-name]#++isCrossChain++#++(address bridge) → bool++` [.item-kind]#internal#

Returns whether the current function call is the result of a
cross-chain message relayed by the `bridge`.

[.contract-item]
[[LibArbitrumL1-crossChainSender-address-]]
==== `[.contract-item-name]#++crossChainSender++#++(address bridge) → address++` [.item-kind]#internal#

Returns the address of the sender that triggered the current
cross-chain message through the `bridge`.

NOTE: {isCrossChain} should be checked before trying to recover the
sender, as it will revert with `NotCrossChainCall` if the current
function call is not the result of a cross-chain message.

:ARBSYS: pass:normal[xref:#LibArbitrumL2-ARBSYS-address[`++ARBSYS++`]]
:isCrossChain: pass:normal[xref:#LibArbitrumL2-isCrossChain-address-[`++isCrossChain++`]]
:crossChainSender: pass:normal[xref:#LibArbitrumL2-crossChainSender-address-[`++crossChainSender++`]]

[.contract]
[[LibArbitrumL2]]
=== `++LibArbitrumL2++` link:https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.9.5/contracts/crosschain/arbitrum/LibArbitrumL2.sol[{github-icon},role=heading-link]

[.hljs-theme-light.nopadding]
```solidity
import "@openzeppelin/contracts/crosschain/arbitrum/LibArbitrumL2.sol";
```

Primitives for cross-chain aware contracts for
https://arbitrum.io/[Arbitrum].

This version should only be used on L2 to process cross-chain messages
originating from L1. For the other side, use {LibArbitrumL1}.

WARNING: There is currently a bug in Arbitrum that causes this contract to
fail to detect cross-chain calls when deployed behind a proxy. This will be
fixed when the network is upgraded to Arbitrum Nitro, currently scheduled for
August 31st 2022.

[.contract-index]
.Functions
--
* {xref-LibArbitrumL2-isCrossChain-address-}[`++isCrossChain(arbsys)++`]
* {xref-LibArbitrumL2-crossChainSender-address-}[`++crossChainSender(arbsys)++`]

--

[.contract-item]
[[LibArbitrumL2-isCrossChain-address-]]
==== `[.contract-item-name]#++isCrossChain++#++(address arbsys) → bool++` [.item-kind]#internal#

[.contract-item]
[[LibArbitrumL2-crossChainSender-address-]]
==== `[.contract-item-name]#++crossChainSender++#++(address arbsys) → address++` [.item-kind]#internal#

Returns the address of the sender that triggered the current
cross-chain message through `arbsys`.

NOTE: {isCrossChain} should be checked before trying to recover the
sender, as it will revert with `NotCrossChainCall` if the current
function call is not the result of a cross-chain message.

:isCrossChain: pass:normal[xref:#LibOptimism-isCrossChain-address-[`++isCrossChain++`]]
:crossChainSender: pass:normal[xref:#LibOptimism-crossChainSender-address-[`++crossChainSender++`]]

[.contract]
[[LibOptimism]]
=== `++LibOptimism++` link:https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.9.5/contracts/crosschain/optimism/LibOptimism.sol[{github-icon},role=heading-link]

[.hljs-theme-light.nopadding]
```solidity
import "@openzeppelin/contracts/crosschain/optimism/LibOptimism.sol";
```

Primitives for cross-chain aware contracts for https://www.optimism.io/[Optimism].
See the https://community.optimism.io/docs/developers/bridge/messaging/#accessing-msg-sender[documentation]
for the functionality used here.

[.contract-index]
.Functions
--
* {xref-LibOptimism-isCrossChain-address-}[`++isCrossChain(messenger)++`]
* {xref-LibOptimism-crossChainSender-address-}[`++crossChainSender(messenger)++`]

--

[.contract-item]
[[LibOptimism-isCrossChain-address-]]
==== `[.contract-item-name]#++isCrossChain++#++(address messenger) → bool++` [.item-kind]#internal#

Returns whether the current function call is the result of a
cross-chain message relayed by `messenger`.

[.contract-item]
[[LibOptimism-crossChainSender-address-]]
==== `[.contract-item-name]#++crossChainSender++#++(address messenger) → address++` [.item-kind]#internal#

Returns the address of the sender that triggered the current
cross-chain message through `messenger`.

NOTE: {isCrossChain} should be checked before trying to recover the
sender, as it will revert with `NotCrossChainCall` if the current
function call is not the result of a cross-chain message.