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Function Signature

func ApplyRPCOverrides(chains []Chain, overrides map[string]string) []Chain
Applies custom RPC URL overrides from a map to the given chains. This allows integrating packages to customize RPC endpoints based on their configuration, such as using private RPC providers with API keys.

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Parameters

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chains
[]Chain
required
Array of Chain structs to apply overrides to. Typically obtained from GetChains(), GetMainnetChains(), or GetTestnetChains()
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overrides
map[string]string
required
Map where keys are chain names and values are the override RPC URLs. Use chain name constants for type safety (e.g., cctp.Ethereum, cctp.Arbitrum)

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Returns

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chains
[]Chain
A new array of Chain structs with RPC URLs overridden where specified. The original chains slice is not mutated.Behavior:
  • Matching chain names have their RPC field replaced with the override URL
  • Empty string overrides are ignored (original RPC is preserved)
  • Non-matching chain names are ignored
  • Chains without overrides retain their default RPC URLs
  • If overrides map is empty, returns the original chains unchanged

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Usage Example

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Basic Override

package main

import (
    "fmt"
    "github.com/circlefin/cctp-go"
)

func main() {
    // Get chains with default RPC endpoints
    chains := cctp.GetChains(false) // false = mainnet
    
    // Define custom RPC endpoints using chain name constants
    customRPCs := map[string]string{
        cctp.Ethereum: "https://eth-mainnet.g.alchemy.com/v2/YOUR_API_KEY",
        cctp.Arbitrum: "https://arb-mainnet.g.alchemy.com/v2/YOUR_API_KEY",
        cctp.Base:     "https://base-mainnet.g.alchemy.com/v2/YOUR_API_KEY",
    }
    
    // Apply RPC overrides
    chains = cctp.ApplyRPCOverrides(chains, customRPCs)
    
    // Now use chains with your custom RPC endpoints
    for _, chain := range chains {
        if chain.Name == cctp.Ethereum {
            fmt.Printf("Ethereum RPC: %s\n", chain.RPC)
            // Output: Ethereum RPC: https://eth-mainnet.g.alchemy.com/v2/YOUR_API_KEY
        }
    }
}

​
Full Example from README

package main

import (
    "github.com/circlefin/cctp-go"
)

func main() {
    // Get chains with default RPC endpoints
    chains := cctp.GetChains(false) // false = mainnet

    // Define custom RPC endpoints using the chain name constants
    // This provides IDE autocomplete and prevents typos
    customRPCs := map[string]string{
        cctp.Ethereum: "https://eth-mainnet.g.alchemy.com/v2/YOUR_API_KEY",
        cctp.Arbitrum: "https://arb-mainnet.g.alchemy.com/v2/YOUR_API_KEY",
        cctp.Base:     "https://base-mainnet.g.alchemy.com/v2/YOUR_API_KEY",
    }

    // Apply RPC overrides
    chains = cctp.ApplyRPCOverrides(chains, customRPCs)

    // Now use chains with your custom RPC endpoints
    for _, chain := range chains {
        if chain.Name == cctp.Ethereum {
            fmt.Printf("Ethereum RPC: %s\n", chain.RPC)
        }
    }
}

​
Configuration-based Overrides

package main

import (
    "fmt"
    "os"
    "github.com/circlefin/cctp-go"
)

func main() {
    // Load custom RPC URLs from environment variables or config
    customRPCs := make(map[string]string)
    
    if ethRPC := os.Getenv("ETH_RPC_URL"); ethRPC != "" {
        customRPCs[cctp.Ethereum] = ethRPC
    }
    if arbRPC := os.Getenv("ARB_RPC_URL"); arbRPC != "" {
        customRPCs[cctp.Arbitrum] = arbRPC
    }
    if baseRPC := os.Getenv("BASE_RPC_URL"); baseRPC != "" {
        customRPCs[cctp.Base] = baseRPC
    }
    
    // Get chains and apply overrides
    chains := cctp.GetChains(false)
    chains = cctp.ApplyRPCOverrides(chains, customRPCs)
    
    // Chains now use custom RPCs where configured, defaults otherwise
    fmt.Printf("Using %d chains\n", len(chains))
}

​
Testnet Overrides

package main

import (
    "github.com/circlefin/cctp-go"
)

func main() {
    // Get testnet chains
    chains := cctp.GetChains(true) // true = testnet
    
    // Override testnet RPC endpoints
    customRPCs := map[string]string{
        cctp.EthereumSepolia: "https://eth-sepolia.g.alchemy.com/v2/YOUR_API_KEY",
        cctp.BaseSepolia:     "https://base-sepolia.g.alchemy.com/v2/YOUR_API_KEY",
    }
    
    chains = cctp.ApplyRPCOverrides(chains, customRPCs)
    
    // Use testnet chains with custom RPCs
}

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Available Chain Constants

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Mainnet

cctp.Ethereum, cctp.Avalanche, cctp.OPMainnet, cctp.Arbitrum, cctp.Base, cctp.PolygonPoS, cctp.Unichain, cctp.Linea, cctp.Codex, cctp.Sonic, cctp.WorldChain, cctp.Sei, cctp.XDC, cctp.HyperEVM, cctp.Ink, cctp.Plume

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Testnet

cctp.EthereumSepolia, cctp.AvalancheFuji, cctp.OPSepolia, cctp.ArbitrumSepolia, cctp.BaseSepolia, cctp.PolygonPoSAmoy, cctp.LineaSepolia, cctp.ArcTestnet, cctp.UnichainSepolia, cctp.CodexTestnet, cctp.SonicTestnet, cctp.WorldChainSepolia, cctp.SeiTestnet, cctp.XDCApothem, cctp.HyperEVMTestnet, cctp.InkTestnet, cctp.PlumeTestnet

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Important Notes

Immutability: The original chains slice is not mutated. The function returns a new slice with the overrides applied.
Empty Overrides: Empty string overrides are ignored, preserving the original RPC URL for that chain.
Type Safety: Use the chain name constants (e.g., cctp.Ethereum) for IDE autocomplete support and to avoid typos. String literals are still supported but must match exactly (case-sensitive).
No-op Behavior: If the overrides map is empty, the function returns the original chains unchanged.

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Best Practices

  1. Use constants: Always use chain name constants for map keys to prevent typos
  2. Environment-based: Load RPC URLs from environment variables or configuration files
  3. Validation: Validate RPC URLs before passing them to this function
  4. Fallback: The default RPC URLs are always available as fallbacks
  5. Security: Never hardcode API keys; use environment variables or secure configuration

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