# Router Calls

The base `userCmd()` treates the calling address (`msg.sender`) as the owner of the call for crediting/debiting the output/input of transactions and assigning ownership of LP positions and surplus collateral. However Ambient supports allowing for a third-party smart contract (*router*) to execute arbitrary commands on the user's behalf. 

### Invocation

In most cases whatever the user wants to do can be accomplished by directly calling the `CrocSwapDex` contract. But Ambient also allows users to authorize an intermediate smart contract to call Ambient on their behalf. Router calls on behalf of users will execute as if a user had directly called `userCmd` on the Ambient contract. The method to do this is:

```
function userCmdRouter (
  uint16 callpathIdx, 
  bytes calldata cmd, 
  address client)
  returns (bytes memory)
```

`callpathIdx` and `cmd` are the same parameters that would be passed to the standard `userCmd` and will behave identically.

`client` is the address of the end user the router is calling on behalf. 

### Approval

Before a router call is invoked, the user ***must*** previously approve the specific smart contract address making the call. Otherwise the contract call will revert. The user must either directly call the approve command.

```
userCmd(0, abi.encode(
  72,         // Fixed initPool subcode  
  router,     // address
  nCalls,     // uint32
  callpaths,  // uint16[]
)
```

`nCalls` is the number of calls the router is approved to make on a user's behalf. Setting this value to the 32-bit maximum will approve the router for an unlimited number of calls (which reduces the gas overhead from decrementing a router's call count). To revoke approval, this value can be set to 0.

`callpaths` are the proxy index calls the router contract is approved for. For example to only approve the router contract to perform swaps this value would be set to `[1]` (the swap proxy contract index)


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