smom-dbis-138/docs/ccip-integration/chain138/CHAIN_SELECTOR.md

CCIP Chain Selector Calculation for ChainID 138

Date: 2025-01-27
Chain ID: 138
Network: DeFi Oracle Meta Mainnet

Automation: Run scripts/ccip/calculate-chain-selector.sh to compute or verify the Chain 138 selector.

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Overview

CCIP chain selectors are unique identifiers used to route messages between chains in the Chainlink CCIP network. For ChainID 138, we need to calculate or define a chain selector that is consistent and unique.

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Calculation Methods

Method 1: Simple ChainID (Recommended for Custom CCIP)

For custom CCIP router implementations, the simplest approach is to use the chain ID directly as the selector:

Chain Selector = Chain ID (as uint64)
Chain Selector = 138
Hex Format: 0x000000000000008a

Advantages:

• Simple and deterministic
• Easy to remember and verify
• Compatible with custom CCIP implementations
• No calculation required

Usage:

uint64 chainSelector = 138; // or 0x000000000000008a

Method 2: Chainlink Official Format

If integrating with Chainlink's official CCIP network, chain selectors are calculated using a deterministic hash-based method. The exact formula used by Chainlink is:

uint64(uint256(keccak256(abi.encodePacked(chainId, "CCIP"))) >> 192)

However, for custom chains not yet registered with Chainlink, you may need to:

1. Register the chain with Chainlink
2. Use Chainlink's assigned selector
3. Or use a custom format for your implementation

Method 3: Deterministic Hash-Based

For a deterministic but more complex selector, you can use:

# Using cast (Foundry)
cast keccak "$(printf '0x%064x' 138)CCIP"
# Extract first 8 bytes (uint64) from the hash

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Recommended Selector for ChainID 138

Selected Method: Method 1 (Simple ChainID)

Selector Value:

• Decimal: 138
• Hex: 0x000000000000008a
• Type: uint64

Rationale:

• Simple and deterministic
• Easy to verify and document
• Compatible with custom CCIP router implementation
• No external dependencies or calculations

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Implementation

Environment Variable

CHAIN138_SELECTOR=0x000000000000008a
# Or simply:
CHAIN138_SELECTOR=138

In Solidity

uint64 constant CHAIN138_SELECTOR = 138;
// Or
uint64 constant CHAIN138_SELECTOR = 0x000000000000008a;

In Scripts

# Use the calculated selector
CHAIN138_SELECTOR=138
# Or hex format
CHAIN138_SELECTOR=0x000000000000008a

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Usage in CCIP Configuration

Router Configuration

When configuring the CCIP Router to support ChainID 138:

router.addSupportedChain(138); // or 0x000000000000008a

Bridge Configuration

When configuring bridges to send to ChainID 138:

bridge.addDestination(138, receiverBridgeAddress);

Message Sending

When sending CCIP messages to ChainID 138:

router.ccipSend(138, message);

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Verification

To verify the selector is correct:

1. Uniqueness: Ensure no other chain uses selector 138
2. Consistency: Use the same selector across all configurations
3. Documentation: Document the selector in all relevant files

Verification Script

Run the calculation script to verify:

./scripts/ccip/calculate-chain-selector.sh

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Integration with Other Chains

When configuring bidirectional bridges, ensure:

1. ChainID 138 → Ethereum Mainnet:

   • Source selector: 138
   • Destination selector: 5009297550715157269 (Ethereum Mainnet)

2. Ethereum Mainnet → ChainID 138:

   • Source selector: 5009297550715157269
   • Destination selector: 138

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Chain Selector Reference Table

Network	Chain ID	CCIP Chain Selector
Ethereum Mainnet	1	5009297550715157269
BSC	56	11344663589394136015
Polygon	137	4051577828743386545
Avalanche	43114	6433500567565415381
Base	8453	15971525489660198786
Arbitrum	42161	4949039107694359620
Optimism	10	3734403246176062136
ChainID 138	138	138 (or 0x000000000000008a)

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Notes

• For custom CCIP implementations, you have flexibility in selector format
• The selector must be consistent across all contracts and configurations
• If integrating with Chainlink's official CCIP, you may need to register the chain
• The selector is used in all CCIP message routing and bridge configurations

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Related Files

• scripts/ccip/calculate-chain-selector.sh - Calculation script
• docs/ETH_WETH_CHAINLINK_GUIDE.md - Main guide with selector reference
• docs/deployment/ENV_EXAMPLE_CONTENT.md - Environment variable examples

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Last Updated: 2025-01-27