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Custom ChainExtensions

ChainExtensions allow chain authors to be able to augment the seal API with additional functions that provide functionality that goes beyond what is provided by the core API. This allows them to tailor seal to their use case. This customization does not modify the seal pallet.


Please check for more specifications.

Ink-log provides pretty log printing for Ink! smart contract,it's implmented by ChainExtension.


In newest pallet-contracts and ink! version, the log feature has been enhanced. So the ink-log is no longer needed.

We advice developer use ink_env::debug_println!(...) instead of this ink-log.


1. Pallet-contracts in Substrate Runtime#

runtime_log: In the ink-log/runtime directory, this library is based on the contents of the function_id and LoggerExt structures passed from ChainExtensions to call the corresponding logs under debug in frame_support to print. It is an implementation library of ink_log prepared for developers of the chain. **For example, chain developers can use it in their own ChainExtensions:

Add this to your Cargo.toml:

runtime-log = { version = "0.1", git = "", default-features = false }
[features]std = [    "runtime-log/std",]


  1. If you already have one CustomExt, use runtime_log::logger_ext! to add to your CustomExt.
pub struct CustomExt;
impl ChainExtension for CustomExt {    fn call<E: Ext>(func_id: u32, env: Environment<E, InitState>) -> Result<RetVal, DispatchError>    where        <E::T as SysConfig>::AccountId: UncheckedFrom<<E::T as SysConfig>::Hash> + AsRef<[u8]>,    {        // TODO add other libs        runtime_log::logger_ext!(func_id, env);
        Ok(RetVal::Converging(0))    }
    fn enabled() -> bool {        true    }}
  1. If you don't have any CustomExt, use runtime_log::LoggerExt to set ChainExtension.
impl pallet_contracts::Config for Runtime {    // ......     type ChainExtension = runtime_log::LoggerExt;}

2. Ink! contract#

ink_log: In the ink-log/contracts directory, provide info!, debug!, warn!, error!, trace!, same as Rust's log library in the same macro, and the call method of the macro is also the same. These macros are packaged implementations of seal_chain_extensions on the ink! side, and are tool library for contract developers. For example, after this library is introduced in the contract Cargo.toml, the log can be printed as follows:

Add this to your contratc Cargo.toml:

ink_log = { git = "", branch = "master", default-features = false, features = ["ink-log-chain-extensions"] }
[features]std = [    "ink_log/std",]

Notes: must add feature ink-log-chain-extensions feature, only when the feature is available, the ink-log functions is effective.


Use like rust log macro

#![cfg_attr(not(feature = "std"), no_std)]
use ink_lang as ink;
#[ink::contract(env = ink_log::CustomEnvironment)]pub mod flipper {    #[ink(storage)]    pub struct Flipper {        value: bool,    }
    impl Flipper {        #[ink(constructor)]        pub fn new(init_value: bool) -> Self {            Self { value: init_value }        }
        #[ink(message)]        pub fn flip(&mut self) {            ink_log::info!(target: "flipper-contract", "latest value is: {}", self.value);                        self.value = !self.value;        }    }}


2020-12-28 17:44:30.274   INFO tokio-runtime-worker flipper-contract:/paritytech/ink/examples/flipper/❤️  latest value is: false

3. log extension func_id#


other func_id refer to

ZKP feature#

Check the zkMega,For examples of related contracts, see metis/groth16