Substrate已經提供了許多預置pallets，用於基於FRAME的執行時。如下圖所示：
例如，FRAME中包含一個balances的pallet，這個pallet透過管理系統中所有賬戶餘額來控制你的區塊鏈系統中的基礎貨幣。如果你想向你的區塊鏈系統中新增智慧合約功能，你只需要包含**合約pallet**即可。
本節我們就是要開發一個存證pallet，並將其新增到我們自定義的區塊鏈中。
3.2.1 建立poe pallet工程目錄
pos => Proof Of Existence
[admin@chaindaily:~/Blockchain/substrate-node-template/pallets] (v2.0.0-rc5)$ cargo new --lib poe
[admin@chaindaily:~/Blockchain/substrate-node-template/pallets/poe] (v2.0.0-rc5)$ tree
.
├── Cargo.toml
└── src
└── lib.rs
3.2.2 程式碼框架
在新生成lib.rs檔案中，填寫以下程式碼框架，這也是從巨集觀角度來講，Substrate pallet可以拆分成的6個部分：
// 1. Imports
use frame_support::{decl_module, decl_storage, decl_event, decl_error, dispatch};
use frame_system::{self as system, ensure_signed};
// 2. Pallet Configuration
pub trait Trait: system::Trait { /* --snip-- */ }
// 3. Pallet Storage Items
decl_storage! { /* --snip-- */ }
// 4. Pallet Events
decl_event! { /* --snip-- */ }
// 5. Pallet Errors
decl_error! { /* --snip-- */ }
// 6. Callable Pallet Functions
decl_module! { /* --snip-- */ }
3.2.3 新增依賴
（1）完善引用
#![cfg_attr(not(feature = "std"), no_std)]
use frame_support::{
decl_module, decl_storage, decl_event, decl_error, ensure, StorageMap
};
use frame_system::{self as system, ensure_signed};
use sp_std::vec::Vec;
（2）完善Cargo.toml檔案
將pallets/template/Cargo.toml複製至pallets/poe目錄，並增加以下內容：
# 增加段
[dependencies.sp-std]
git = 'https://github.com/paritytech/substrate.git'
default-features = false
tag = 'v2.0.0-rc5'
version = '2.0.0-rc5'
[features]
default = ['std']
std = [
'codec/std',
'frame-support/std',
'frame-system/std',
'sp-std/std', # <-- 增加行
]
3.2.4 配置pallet
每一個pallet都有一個配置trait
// 2. Pallet Configuration
pub trait Trait: system::Trait {
/// The overarching event type.
type Event: From<Event<Self>> + Into<<Self as system::Trait>::Event>;
}
3.2.5 定義事件
事件：可以展示pallet成功被呼叫的時間和資訊。
// 4. Pallet Events
decl_event! {
pub enum Event<T> where AccountId = <T as system::Trait>::AccountId {
/// Event emitted when a proof has been claimed.
ClaimCreated(AccountId, Vec<u8>),
/// Event emitted when a claim is revoked by the owner.
ClaimRevoked(AccountId, Vec<u8>),
}
}
我們的存證palet，包含了以下事件：
ClaimCreated：存證建立
ClaimRevoked：存證撤銷
事件可以包含一些附加資料，例如：
AccountId：誰觸發了事件
Vec<u8>：儲存或撤銷的存證資料
3.2.6 定義錯誤
錯誤：可以展示pallet呼叫失敗的時間，及失敗原因。
// 5. Pallet Errors
decl_error! {
pub enum Error for Module<T: Trait> {
/// This proof has already been claimed
ProofAlreadyClaimed,
/// The proof does not exist, so it cannot be revoked
NoSuchProof,
/// The proof is claimed by another account, so caller can't revoke it
NotProofOwner,
}
}
3.2.7 定義儲存
要新增一個新的存證到我們的區塊鏈上，就是要將其儲存到我們的pallet的儲存裡面。在這裡建立我們的儲存結構。
// 3. Pallet Storage Items
decl_storage! {
trait Store for Module<T: Trait> as TemplateModule {
/// The storage item for our proofs.
/// It maps a proof to the user who made the claim and when they made it.
Proofs: map hasher(blake2_128_concat) Vec<u8> => (T::AccountId, T::BlockNumber);
}
}
3.2.8 實現介面
// 6. Callable Pallet Functions
decl_module! {
/// The module declaration.
pub struct Module<T: Trait> for enum Call where origin: T::Origin {
// Initializing errors
// this includes information about your errors in the node's metadata.
// it is needed only if you are using errors in your pallet
type Error = Error<T>;
// A default function for depositing events
fn deposit_event() = default;
/// Allow a user to claim ownership of an unclaimed proof
#[weight = 10_000]
fn create_claim(origin, proof: Vec<u8>) {
// Verify that the incoming transaction is signed and store who the
// caller of this function is.
let sender = ensure_signed(origin)?;
// Verify that the specified proof has not been claimed yet or error with the message
ensure!(!Proofs::<T>::contains_key(&proof), Error::<T>::ProofAlreadyClaimed);
// Call the `system` pallet to get the current block number
let current_block = <system::Module<T>>::block_number();
// Store the proof with the sender and the current block number
Proofs::<T>::insert(&proof, (&sender, current_block));
// Emit an event that the claim was created
Self::deposit_event(RawEvent::ClaimCreated(sender, proof));
}
/// Allow the owner to revoke their claim
#[weight = 10_000]
fn revoke_claim(origin, proof: Vec<u8>) {
// Determine who is calling the function
let sender = ensure_signed(origin)?;
// Verify that the specified proof has been claimed
ensure!(Proofs::<T>::contains_key(&proof), Error::<T>::NoSuchProof);
// Get owner of the claim
let (owner, _) = Proofs::<T>::get(&proof);
// Verify that sender of the current call is the claim owner
ensure!(sender == owner, Error::<T>::NotProofOwner);
// Remove claim from storage
Proofs::<T>::remove(&proof);
// Emit an event that the claim was erased
Self::deposit_event(RawEvent::ClaimRevoked(sender, proof));
}
}
}
3.2.9 完善runtime配置
· 修改runtime/Cargo.toml
# 增加段
[dependencies.poe]
default-features = false
package = 'pallet-poe'
path = '../pallets/poe'
version = '2.0.0-rc5'
[features]
default = ['std']
std = [
'aura/std',
'balances/std',
'codec/std',
'frame-executive/std',
'frame-support/std',
'grandpa/std',
'randomness-collective-flip/std',
'serde',
'sp-api/std',
'sp-block-builder/std',
'sp-consensus-aura/std',
'sp-core/std',
'sp-inherents/std',
'sp-io/std',
'sp-offchain/std',
'sp-runtime/std',
'sp-session/std',
'sp-std/std',
'sp-transaction-pool/std',
'sp-version/std',
'sudo/std',
'system/std',
'timestamp/std',
'transaction-payment/std',
'template/std',
'poe/std', # <-- 增加行
]
· 修改runtime/src/lib.rs
// 增加程式碼塊
impl poe::Trait for Runtime {
type Event = Event;
}
construct_runtime!(
pub enum Runtime where
Block = Block,
NodeBlock = opaque::Block,
UncheckedExtrinsic = UncheckedExtrinsic
{
System: system::{Module, Call, Config, Storage, Event<T>},
RandomnessCollectiveFlip: randomness_collective_flip::{Module, Call, Storage},
Timestamp: timestamp::{Module, Call, Storage, Inherent},
Aura: aura::{Module, Config<T>, Inherent},
Grandpa: grandpa::{Module, Call, Storage, Config, Event},
Balances: balances::{Module, Call, Storage, Config<T>, Event<T>},
TransactionPayment: transaction_payment::{Module, Storage},
Sudo: sudo::{Module, Call, Config<T>, Storage, Event<T>},
TemplateModule: template::{Module, Call, Storage, Event<T>},
PoeModule: poe::{Module, Call, Storage, Event<T>}, // <-- 增加程式碼行
}
);
3.3 node-template節點編譯
完成存證pallet的開發後，需要重新編譯節點。
[admin@chaindaily:~/Blockchain/substrate-node-template] (v2.0.0-rc5)$ cargo build --release
Compiling node-template-runtime v2.0.0-rc5 (/root/Blockchain/substrate-node-template/runtime)
Compiling pallet-poe v2.0.0-rc5 (/root/Blockchain/substrate-node-template/pallets/poe)
Compiling node-template v2.0.0-rc5 (/root/Blockchain/substrate-node-template/node)
Finished release [optimized] target(s) in 12m 18s
3.4 node-template節點啟動
[admin@chaindaily:~/Blockchain/substrate-node-template] (v2.0.0-rc5)$ ./target/release/node-template purge-chain --dev
Are you sure to remove "/root/.local/share/node-template/chains/dev/db"? [y/N]: y
"/root/.local/share/node-template/chains/dev/db" removed.
[admin@chaindaily:~/Blockchain/substrate-node-template] (v2.0.0-rc5)$ ./target/release/node-template --dev --ws-external --rpc-external --rpc-cors=all
2020-08-04 22:23:44 Substrate Node
2020-08-04 22:23:44 version 2.0.0-rc5-8f769db-x86_64-linux-gnu
2020-08-04 22:23:44 by Substrate DevHub <https://github.com/substrate-developer-hub>, 2017-2020
2020-08-04 22:23:44 Chain specification: Development
2020-08-04 22:23:44 Node name: gray-island-3707
2020-08-04 22:23:44 Role: AUTHORITY
2020-08-04 22:23:44 Database: RocksDb at /root/.local/share/node-template/chains/dev/db
2020-08-04 22:23:44 Native runtime: node-template-1 (node-template-1.tx1.au1)
2020-08-04 22:23:44 Initializing Genesis block/state (state: 0x5ea9…1904, header-hash: 0x6dac…f18d)
2020-08-04 22:23:44 Loading GRANDPA authority set from genesis on what appears to be first startup.
2020-08-04 22:23:44 Loaded block-time = 6000 milliseconds from genesis on first-launch
2020-08-04 22:23:44 Highest known block at #0
2020-08-04 22:23:44 Using default protocol ID "sup" because none is configured in the chain specs
2020-08-04 22:23:44 Local node identity is: 12D3KooWBSKitzNNzfSszWXRggcMe44bv6WfyKy9kyM2DwjcjJNr (legacy representation: QmX77kaM8ydN99qjyRTRznRqkHahzi5jX286MnQTqUp3UR)
2020-08-04 22:23:44 Prometheus server started at 127.0.0.1:9615
2020-08-04 22:23:48 Starting consensus session on top of parent 0x6dac7f7bfbd9cbc4e91be19069d230c9b044ef6080d781e6717a9c99e442f18d
2020-08-04 22:23:48 Prepared block for proposing at 1 [hash: 0xd129eea95a079183db3dd87947194add22643588a1fec10e778b93a867d0f161; parent_hash: 0x6dac…f18d; extrinsics (1): [0xc502…67b6]]
2020-08-04 22:23:48 Pre-sealed block for proposal at 1. Hash now 0x2305ab1c8aee785cb991c993e849b79d7231ad8206b0e7e9b75ef17c3ee90b64, previously 0xd129eea95a079183db3dd87947194add22643588a1fec10e778b93a867d0f161.
2020-08-04 22:23:48 Imported #1 (0x2305…0b64)
2020-08-04 22:23:49 Idle (0 peers), best: #1 (0x2305…0b64), finalized #0 (0x6dac…f18d), ⬇ 0 ⬆ 0
2020-08-04 22:23:54 Starting consensus session on top of parent 0x2305ab1c8aee785cb991c993e849b7
