ink! is an embedded domain specific language to write smart contracts in Rust for blockchains built on the Substrate framework. Starting in version 4.0.0 and prior to version 4.2.1, the return value when using delegate call mechanics, either through `CallBuilder::delegate` or `ink_env::invoke_contract_delegate`, is decoded incorrectly. This bug was related to the mechanics around decoding a call's return buffer, which was changed as part of pull request 1450. Since this feature was only released in ink! 4.0.0, no previous versions are affected. Users who have an ink! 4.x series contract should upgrade to 4.2.1 to receive a patch.

Affected: crates.io: ink, crates.io: ink_env

### Summary The return value when using delegate call mechanics, either through [`CallBuilder::delegate`](https://docs.rs/ink_env/4.2.0/ink_env/call/struct.CallBuilder.html#method.delegate) or [`ink_env::invoke_contract_delegate`](https://docs.rs/ink_env/4.2.0/ink_env/fn.invoke_contract_delegate.html), is being decoded incorrectly.

### Description Consider this minimal example:

```rust // First contract, this will be performing a delegate call to the `Callee`. #[ink(storage)] pub struct Caller { value: u128, }

#[ink(message)] pub fn get_value(&self, callee_code_hash: Hash) -> u128 { let result = build_call::<DefaultEnvironment>() .delegate(callee_code_hash) .exec_input(ExecutionInput::new(Selector::new(ink::selector_bytes!( "get_value" )))) .returns::<u128>() .invoke();

result }

// Different contract, using this code hash for the delegate call. #[ink(storage)] pub struct Callee { value: u128, }

#[ink(message)] pub fn get_value(&self) -> u128 { self.value } ```

In this example we are executing the `Callee` code in the context of the `Caller` contract. This means we'll be using the storage values of the `Caller` contract.

Running this code we expect the delegate call to return `value` as it was stored in the `Caller` contract. However, due to the reported bug a different value is returned (for the case of `uint`s it is `256` times the expected value).

### Impact After conducting an analysis of the…