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Use the post_route_handler parameter of /v2/fungible/msgs endpoint to define actions that will be executed on the destination chain after a route transfer or swap is completed. These actions are executed within the same transaction as the original swap or transfer. This handler allows developers to build omni-chain and omni-token workflows where users can swap, liquid stake, deposit, buy an NFT, or take any other action starting from any chain or any token in Cosmos — all in a single transaction. This parameter currently supports:
  1. CosmWasm contract calls on the destination chain
  2. autopilot support for liquid staking interactions on Stride

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Background Info

All post_route actions must have the following characteristics:
  • Permissionless: Skip Go can only support permissionless actions because the underlying protocols (e.g. IBC hooks, IBC callbacks, packet-forward-middleware) derive the addresses they use to call contracts based on the origin of the transfer. Skip Go supports both ibc-hooks and ibc-callbacks depending on which module the destination chain has implemented (they are incompatible approaches), automatically generating the appropriate message payloads for each. This means one user originating on two different chains or starting with two different tokens will eventually call the final contract / module with different addresses. You can only reliably permission actions that you know will 1) always originate on the same chain and 2) always take the same path to the destination chain. In general, we recommend not making this assumption unless you are an interoperability expert
  • Single-token input: The underlying IBC transfer protocol (ICS-20) doesn’t support transfers of more than 1 token denom in a single transfer message, so we can only send 1 token denom to the final contract or module at a time. This means the contract or module in the post_route_handler must not require multiple token denoms sent to it simultaneously. For example, a classic LP action where the user must provide tokens in both sides of the pool simultaneously would not work.
Use authority-delegation with local address for permissionless actions that enable permissioned follow-upsCommonly, the first interaction with a contract is permissionless, but it awards the end-user some kind of permissioned authority to perform follow-on actions (e.g. staking enables unstaking + collecting rewards; depositing enables withdrawing and earning yield) or receipt tokens (e.g. LPing produces LP receipt tokens).As a cross-chain caller, you should generally avoid contracts that implicitly delegate these authorities or give receipt tokens to the caller because the caller will depend on the path the user has taken over IBC. You should look for contracts to imply authority delegation — i.e. contracts that explicitly assign permissions to an address in the calldata that may be different than the caller and address sending the tokens. Examples of this pattern are:
  • Astroport’s receiver parameter in the provide_liquidity message
  • Mars’ on_behalf_of parameter in the deposit message
  • Astroport’s to parameter in the swap message
We recommend setting these authority delegation parameters to the user’s local address on the destination chain, so they can perform future actions locally.

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CosmWasm

To call a CosmWasm contract on the destination chain, the following requirements must be satisfied:
  1. The destination chain supports CosmWasm & either ibc-hooks or ibc-callbacks.
  2. The chain in the route immediately before the destination chain supports IBC memos as well as packet-forward-middleware.
To specify a CosmWasm contract call on the destination chain, pass a wasm_msg as the post_route_handler in the /v2/fungible/msgs call with:
  • contract_address: The target contract address
  • msg: JSON string of the message to pass to the contract
In addition, set the destination address in the address_list to the address of the contract. For example, this is a request for a transfer of USDC from Axelar to Neutron, with a post-route handler that swaps the USDC to Neutron using an Astroport pool on Neutron: 
{
  "source_asset_denom": "uusdc",
  "source_asset_chain_id": "axelar-dojo-1",
  "dest_asset_denom": "ibc/F082B65C88E4B6D5EF1DB243CDA1D331D002759E938A0F5CD3FFDC5D53B3E349",
  "dest_asset_chain_id": "neutron-1",
  "amount_in": "1000000",
  "amount_out": "1000000",
  "address_list": [
    "axelar1x8ad0zyw52mvndh7hlnafrg0gt284ga7u3rez0",
    "neutron1l3gtxnwjuy65rzk63k352d52ad0f2sh89kgrqwczgt56jc8nmc3qh5kag3"
  ],
  "operations": [
    {
      "transfer": {
        "port": "transfer",
        "channel": "channel-78",
        "chain_id": "axelar-dojo-1",
        "pfm_enabled": false,
        "dest_denom": "ibc/F082B65C88E4B6D5EF1DB243CDA1D331D002759E938A0F5CD3FFDC5D53B3E349",
        "supports_memo": true
      }
    }
  ],
  "post_route_handler": {
    "wasm_msg": {
      "contract_address": "neutron1l3gtxnwjuy65rzk63k352d52ad0f2sh89kgrqwczgt56jc8nmc3qh5kag3",
        "msg": "{\"swap\":{\"offer_asset\":{\"info\":{\"native_token\":{\"denom\":\"ibc/F082B65C88E4B6D5EF1DB243CDA1D331D002759E938A0F5CD3FFDC5D53B3E349\"}},\"amount\":\"10000\"},\"to\":\"neutron1x8ad0zyw52mvndh7hlnafrg0gt284ga7uqunnf\"}}"
    }
  }
}
Note that the last address provided in the address_list is the address of the pool contract on Neutron, rather than a user address. The message returned from this request uses ibc-hooks on Neutron to perform the CosmWasm contract call atomically with the IBC transfer.

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Autopilot

To use Autopilot after route actions, the following requirements must be satisfied:
  1. The destination chain supports the autopilot module. Currently, this means the destination chain must be stride-1.
  2. The chain in the route immediately before the destination chain supports IBC memos as well as packet-forward-middleware.
To specify an Autopilot action on the destination chain, pass a autopilot_msg as the post_route_handler in the /v2/fungible/msgs call with:
  • receiver: Set to the address on behalf of which you’re performing the action
  • action: An enum giving the action that you wish to execute
    • This may be one of LIQUID_STAKE (for liquid staking an asset) or CLAIM for updating airdrop claim addresses.
For example, this is a request for a transfer of ATOM from Cosmos Hub to Stride, with a post-route handler that atomically liquid stakes the transferred ATOM on Stride, sending stATOM to the specific receiver on Stride: 
{
  "source_asset_denom": "uatom",
  "source_asset_chain_id": "cosmoshub-4",
  "dest_asset_denom": "ibc/27394FB092D2ECCD56123C74F36E4C1F926001CEADA9CA97EA622B25F41E5EB2",
  "dest_asset_chain_id": "stride-1",
  "amount_in": "1000000",
  "amount_out": "1000000",
  "address_list": [
    "cosmos1x8ad0zyw52mvndh7hlnafrg0gt284ga7cl43fw",
    "stride1x8ad0zyw52mvndh7hlnafrg0gt284ga7m54daz"
  ],
  "operations": [
    {
      "transfer": {
        "port": "transfer",
        "channel": "channel-391",
        "chain_id": "cosmoshub-4",
        "pfm_enabled": true,
        "dest_denom": "ibc/27394FB092D2ECCD56123C74F36E4C1F926001CEADA9CA97EA622B25F41E5EB2",
        "supports_memo": true
      }
    }
  ],
  "post_route_handler": {
    "autopilot_msg": {
      "receiver": "stride1x8ad0zyw52mvndh7hlnafrg0gt284ga7m54daz",
      "action": "LIQUID_STAKE"
    }
  }
}
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