> For the complete documentation index, see [llms.txt](https://docs.yarchain.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.yarchain.org/dev-docs/hello-world.md).

# Hello world!

{% hint style="info" %}
More examples can be found here: [https://github.com/YARlabs/YAR-v2-contracts/](https://github.com/YARlabs/YAR-v2-contracts/tree/main)
{% endhint %}

```solidity
// SPDX-License-Identifier: UNLICENSED
pragma solidity 0.8.20;

import { YarLib } from "../../YarLib.sol";
import { YarRequest } from "../../YarRequest.sol";
import { YarResponse } from "../../YarResponse.sol";

contract YarBridgeMessage {
    address public owner;
    uint256 public chainId;
     
    address public yarRequest;
    address public yarResponse;
    
    mapping(uint256 chainId => address peer) public peers;
    function setPeer(uint256 newChainId, address newPeer) external {
        require(msg.sender == owner, "only owner!");
        peers[newChainId] = newPeer;
    }

    function getPeer(uint256 _chainId) public view returns (address) {
        address peer = peers[_chainId];
        return peer == address(0) ? address(this) : peer;
    }
 
    constructor(
        address intialYarRequest,
        address intialYarResponse
    )
    {
        yarRequest = intialYarRequest;
        yarResponse = intialYarResponse;
        chainId = block.chainid;
        owner = msg.sender;
    }
 
    function sendTo(
        uint256 targetChainId,
        address receiver,
        string memory message
    )
    
    external returns (YarLib.YarTX memory) {
        bytes memory targetTx = abi.encodeWithSelector(
            YarBridgeMessage.sendFrom.selector,
            msg.sender,
            receiver,
            message
        );

        YarLib.YarTX memory yarTx = YarLib.YarTX(
            chainId,
            address(this),
            msg.sender,
            targetChainId,
            getPeer(targetChainId),
            0,
            targetTx,
            0
        );

        YarRequest(yarRequest).send(yarTx);

        return yarTx;
    }

    struct Message {
        address sender;
        address receiver;
        string message;
        uint256 timestamp;
    }
 
    Message[] public messages;
    uint256 public messageCount;
 
    function getMessages(address receiver, address sender, uint offset, uint limit) public view returns (Message[] memory) {
        require(offset < messageCount, "Offset out of range");
        
        uint end = offset + limit;
        if (end > messageCount) {
            end = messageCount;
        }

        uint resultSize = end - offset;
        Message[] memory result = new Message[](resultSize);

        uint index = 0;
        for (uint i = messageCount - offset; i > messageCount - end; i--) {
            if (messages[i - 1].receiver == receiver) {
                result[index] = messages[i - 1];
                index++;
            } else if (messages[i - 1].sender == sender) {
                result[index] = messages[i - 1];
                index++;
            }
        }

        return result;
    }
 
    function sendFrom(
        address sender,
        address receiver,
        string calldata message
    ) external {
        require(msg.sender == yarResponse, "Only YarResponse!");

        YarLib.YarTX memory trustedYarTx = YarResponse(yarResponse).trustedYarTx();
        require(getPeer(trustedYarTx.initialChainId) == trustedYarTx.sender, "not peer!");

        messages.push(Message(
            sender,
            receiver,
            message,
            block.timestamp
        ));
        messageCount++;
    }
}
```


---

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