> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cosmos.network/llms.txt
> Use this file to discover all available pages before exploring further.

# Messages

> Uploading the Wasm light client contract to the Wasm VM storage is achieved by means of MsgStoreCode:

## `MsgStoreCode`

Uploading the Wasm light client contract to the Wasm VM storage is achieved by means of `MsgStoreCode`:

```go theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
type MsgStoreCode struct {
  / signer address
  Signer string
  / wasm byte code of light client contract. It can be raw or gzip compressed
  WasmByteCode []byte
}
```

This message is expected to fail if:

* `Signer` is an invalid Bech32 address, or it does not match the designated authority address.
* `WasmByteCode` is empty or it exceeds the maximum size, currently set to 3MB.

Only light client contracts stored using `MsgStoreCode` are allowed to be instantiated. An attempt to create a light client from contracts uploaded via other means (e.g. through `x/wasm` if the module shares the same Wasm VM instance with 08-wasm) will fail. Due to the idempotent nature of the Wasm VM's `StoreCode` function, it is possible to store the same byte code multiple times.

When execution of `MsgStoreCode` succeeds, the checksum of the contract (i.e. the sha256 hash of the contract's byte code) is stored in an allow list. When a relayer submits [`MsgCreateClient`](https://github.com/cosmos/ibc-go/blob/v8.0.0/proto/ibc/core/client/v1/tx.proto#L25-L37) with 08-wasm's `ClientState`, the client state includes the checksum of the Wasm byte code that should be called. Then 02-client calls [08-wasm's implementation of `Initialize` function](https://github.com/cosmos/ibc-go/blob/06fd8eb5ee1697e3b43be7528a6e42f5e4a4613c/modules/core/02-client/keeper/client.go#L40) (which is an interface function part of `LightClientModule`), and it will check that the checksum in the client state matches one of the checksums in the allow list. If a match is found, the light client is initialized; otherwise, the transaction is aborted.

## `MsgMigrateContract`

Migrating a contract to a new Wasm byte code is achieved by means of `MsgMigrateContract`:

```go theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
type MsgMigrateContract struct {
  / signer address
  Signer string
  / the client id of the contract
  ClientId string
  / the SHA-256 hash of the new wasm byte code for the contract
  Checksum []byte
  / the json-encoded migrate msg to be passed to the contract on migration
  Msg []byte
}
```

This message is expected to fail if:

* `Signer` is an invalid Bech32 address, or it does not match the designated authority address.
* `ClientId` is not a valid identifier prefixed by `08-wasm`.
* `Checksum` is not exactly 32 bytes long or it is not found in the list of allowed checksums (a new checksum is added to the list when executing `MsgStoreCode`), or it matches the current checksum of the contract.

When a Wasm light client contract is migrated to a new Wasm byte code the checksum for the contract will be updated with the new checksum.

## `MsgRemoveChecksum`

Removing a checksum from the list of allowed checksums is achieved by means of `MsgRemoveChecksum`:

```go theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
type MsgRemoveChecksum struct {
  / signer address
  Signer string
  / Wasm byte code checksum to be removed from the store
  Checksum []byte
}
```

This message is expected to fail if:

* `Signer` is an invalid Bech32 address, or it does not match the designated authority address.
* `Checksum` is not exactly 32 bytes long or it is not found in the list of allowed checksums (a new checksum is added to the list when executing `MsgStoreCode`).

When a checksum is removed from the list of allowed checksums, then the corresponding Wasm byte code will not be available for instantiation in [08-wasm's implementation of `Initialize` function](https://github.com/cosmos/ibc-go/blob/v8.0.0/modules/core/02-client/keeper/client.go#L36).