使用自己的函数读取程序状态

在本课程中，你将学习如何在区块链交易中使用托管智能合约，以增加各方的安全性。

你将了解如何使用托管智能合约的过程，从同意条款到将资金自动转移到卖方的数字钱包。

让我们通过添加程序元数据来扩展我们的托管程序的功能。我们将从在托管程序的目录中创建一个 escrow-io 包开始：

cargo new io --lib

escrow-io 包的 Cargo.toml 文件将包含以下内容：

io/Cargo.toml

[package]
name = "escrow-io"
version = "0.1.0"
edition = "2021"

[dependencies]
gmeta = { git = "https://github.com/gear-tech/gear.git", tag = "v1.4.1" }
gstd = { git = "https://github.com/gear-tech/gear.git", tag = "v1.4.1" }
parity-scale-codec = { version = "3", default-features = false }
scale-info = { version = "2", default-features = false }

现在，我们可以将 InitEscrow、 EscrowAction、 EscrowEvent、 EscrowState 和 Escrow 移动到 escrow-io 包中，并定义 ProgramMetadata 如下：

io/src/lib.rs

#![no_std]

use gmeta::{In, InOut, Metadata, Out};
use gstd::{prelude::*, ActorId};
use scale_info::TypeInfo;

pub struct ProgramMetadata;

impl Metadata for ProgramMetadata {
    type Init = In<InitEscrow>;
    type Handle = InOut<EscrowAction, EscrowEvent>;
    type Reply = ();
    type Others = ();
    type Signal = ();
    type State = Out<Escrow>;
}

#[derive(Encode, Decode, TypeInfo)]
pub struct InitEscrow {
    pub seller: ActorId,
    pub buyer: ActorId,
    pub price: u128,
}

#[derive(Encode, Decode, TypeInfo)]
pub enum EscrowAction {
    Deposit,
    ConfirmDelivery,
}

#[derive(Encode, Decode, TypeInfo)]
pub enum EscrowEvent {
    FundsDeposited,
    DeliveryConfirmed,
}

#[derive(Default, Debug, PartialEq, Eq, Encode, Decode, TypeInfo)]
pub enum EscrowState {
    #[default]
    AwaitingPayment,
    AwaitingDelivery,
    Closed,
}

#[derive(Default, Encode, Decode, TypeInfo)]
pub struct Escrow {
    pub seller: ActorId,
    pub buyer: ActorId,
    pub price: u128,
    pub state: EscrowState,
}

要向 escrow 包添加状态函数，我们需要包含以下内容：

src/lib.rs

#[no_mangle]
extern "C" fn state() {
    let escrow = unsafe {
        ESCROW.get_or_insert(Default::default())
    };
    msg::reply(escrow, 0).expect("Failed to share state");
}

然后，在托管程序的 Cargo.toml 中添加依赖项：

Cargo.toml

[package]
name = "escrow"
version = "0.1.0"
edition = "2021"

[dependencies]
gstd = { git = "https://github.com/gear-tech/gear.git", tag = "v1.4.1", features = ["debug"] }
parity-scale-codec = { version = "3", default-features = false }
scale-info = { version = "2", default-features = false }
escrow-io = { path = "io" }

[build-dependencies]
gear-wasm-builder = { git = "https://github.com/gear-tech/gear.git", tag = "v1.4.1", features = ["wasm-opt"] }
escrow-io = { path = "io" }

[dev-dependencies]
gtest = { git = "https://github.com/gear-tech/gear.git", tag = "v1.4.1" }

我们将更改 build.rs 文件：

build.rs

fn main() {
    gear_wasm_builder::build_with_metadata::<escrow_io::ProgramMetadata>();
}

并创建一个独立的包来读取状态：

cargo new state --lib

这个包的 Cargo.toml 将包含以下内容：

state/Cargo.toml

[package]
name = "escrow-state"
version = "0.1.0"
edition = "2021"

[dependencies]
gmeta = {  git = "https://github.com/gear-tech/gear.git", tag = "v1.4.1", features = ["codegen"] }
gstd = { git = "https://github.com/gear-tech/gear.git", tag = "v1.4.1" }
parity-scale-codec = { version = "3", default-features = false }
scale-info = { version = "2", default-features = false }
escrow-io = { path = "../io" }

[build-dependencies]
gear-wasm-builder = { git = "https://github.com/gear-tech/gear.git", tag = "v1.4.1", features = ["metawasm", "wasm-opt"] }

在 lib.rs 文件中，我们应该如下定义 metafns 模块：

state/src/lib.rs

#![no_std]
use gmeta::metawasm;
use gstd::{prelude::*, ActorId};
use escrow_io::*;

#[metawasm]
pub mod metafns {
    // ...
}

还需要定义程序状态的类型，这种情况下是 Escrow 类型。我们可以通过添加 type State = Escrow来完成：

state/src/lib.rs

#![no_std]
use gmeta::metawasm;
use gstd::{prelude::*, ActorId};
use escrow_io::*;

#[metawasm]
pub mod metafns {
    pub type State = Escrow;
    // ...
}

在定义了 trait 和状态类型之后，我们可以编写与 Escrow 状态相关的任何函数。例如：

state/src/lib.rs

#![no_std]
use gmeta::metawasm;
use gstd::{prelude::*, ActorId};
use escrow_io::*;

#[metawasm]
pub mod metafns {
    pub type State = Escrow;

    pub fn seller(state: State) -> ActorId {
        state.seller
    }

    pub fn buyer(state: State) -> ActorId {
        state.buyer
    }

    pub fn escrow_state(state: State) -> EscrowState {
        state.state
    }
}

最后，我们将创建该状态的 build.rs 文件如下：

state/build.rs

fn main() {
    gear_wasm_builder::build_metawasm();
}

一旦构建了包，我们将在我们的 UI 应用程序中使用 escrow_state.meta.wasm 文件与智能合约进行交互。