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https://github.com/near/near-sdk-rs

Rust library for writing NEAR smart contracts
https://github.com/near/near-sdk-rs

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Rust library for writing NEAR smart contracts

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near-sdk



  


    Rust library for writing NEAR smart contracts.

  


  


    Previously known as near-bindgen.

  



  


    Reference Documentation

    MSRV

    Crates.io version

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      Features

       | 

      Pre-requisites

       | 

      Writing Rust Contract

       | 

      Building Rust Contract

       | 

      Reference Documentation

       | 

      Contributing

    





## Release notes



**Release notes and unreleased changes can be found in the [CHANGELOG](https://github.com/near/near-sdk-rs/blob/master/CHANGELOG.md)**



## Example



Wrap a struct in `#[near]` and it generates a smart contract compatible with the NEAR blockchain:

```rust

use near_sdk::{near, env};



#[near(contract_state)]

#[derive(Default)]

pub struct StatusMessage {

    records: HashMap,

}



#[near]

impl StatusMessage {

    pub fn set_status(&mut self, message: String) {

        let account_id = env::signer_account_id();

        self.records.insert(account_id, message);

    }



    pub fn get_status(&self, account_id: AccountId) -> Option {

        self.records.get(&account_id).cloned()

    }

}

```



## Features



### Unit-testable

Writing unit tests is easy with `near-sdk`:



```rust

#[test]

fn set_get_message() {

    let mut contract = StatusMessage::default();

    contract.set_status("hello".to_string());

    assert_eq!("hello".to_string(), contract.get_status("bob_near".to_string()).unwrap());

}

```



Run unit test the usual way:

```sh

cargo test --package status-message

```



### Asynchronous cross-contract calls

Asynchronous cross-contract calls allow parallel execution of multiple contracts in parallel with subsequent aggregation on another contract. `env` exposes the following methods:

* `promise_create` -- schedules an execution of a function on some contract;

* `promise_then` -- attaches the callback back to the current contract once the function is executed;

* `promise_and` -- combinator, allows waiting on several promises simultaneously, before executing the callback;

* `promise_return` -- treats the result of execution of the promise as the result of the current function.



Follow [examples/cross-contract-high-level](https://github.com/near/near-sdk-rs/tree/master/examples/cross-contract-calls/high-level)

to see various usages of cross contract calls, including **system-level actions** done from inside the contract like balance transfer (examples of other system-level actions are: account creation, access key creation/deletion, contract deployment, etc).



### Initialization methods

We can define an initialization method that can be used to initialize the state of the contract. `#[init]` verifies that the contract has not been initialized yet (the contract state doesn't exist) and will panic otherwise.



```rust

#[near]

impl StatusMessage {

    #[init]

    pub fn new(user: String, status: String) -> Self {

        let mut res = Self::default();

        res.records.insert(user, status);

        res

    }

}

```



Even if you have initialization method your smart contract is still expected to derive `Default` trait. If you don't

want to disable default initialization, then you can prohibit it like this:

```rust

impl Default for StatusMessage {

    fn default() -> Self {

        near_sdk::env::panic_str("Contract should be initialized before the usage.")

    }

}

```

You can also prohibit `Default` trait initialization by using `near_sdk::PanicOnDefault` helper macro. E.g.:

```rust

#[near(contract_state)]

#[derive(PanicOnDefault)]

pub struct StatusMessage {

    records: HashMap,

}

```



### Payable methods

We can allow methods to accept token transfer together with the function call. This is done so that contracts can define a fee in tokens that needs to be paid when they are used. By the default the methods are not payable and they will panic if someone will attempt to transfer tokens to them during the invocation. This is done for safety reason, in case someone accidentally transfers tokens during the function call.



To declare a payable method simply use `#[payable]` decorator:

```rust



#[payable]

pub fn my_method(&mut self) {

...

}

```



### Private methods

Usually, when a contract has to have a callback for a remote cross-contract call, this callback method should

only be called by the contract itself. It's to avoid someone else calling it and messing the state. Pretty common pattern

is to have an assert that validates that the direct caller (predecessor account ID) matches to the contract's account (current account ID).

Macro `#[private]` simplifies it, by making it a single line macro instead and improves readability.



To declare a private method use `#[private]` decorator:

```rust



#[private]

pub fn my_method(&mut self) {

...

}

/// Which is equivalent to



pub fn my_method(&mut self ) {

    if near_sdk::env::current_account_id() != near_sdk::env::predecessor_account_id() {

        near_sdk::env::panic_str("Method my_method is private");

    }

...

}

```



Now, only the account of the contract itself can call this method, either directly or through a promise.



## Pre-requisites

To develop Rust contracts you would need to:

* Install [Rustup](https://rustup.rs/):

```sh

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

```

* Add wasm target to your toolchain:

```sh

rustup target add wasm32-unknown-unknown

```



## Writing Rust Contract

You can follow the [examples/status-message](https://github.com/near/near-sdk-rs/tree/master/examples/status-message) crate that shows a simple Rust contract.



The general workflow is the following:

1. Create a crate and configure the `Cargo.toml` similarly to how it is configured in [examples/status-message/Cargo.toml](https://github.com/near/near-sdk-rs/tree/master/examples/status-message/Cargo.toml);

2. Crate needs to have one `pub` struct that will represent the smart contract itself:

    * The struct needs to implement `Default` trait which

    NEAR will use to create the initial state of the contract upon its first usage;



   Here is an example of a smart contract struct:

   ```rust

   use near_sdk::{near, env};



   #[near(contract_state)]

   #[derive(Default)]

   pub struct MyContract {

       data: HashMap

   }

   ```



3. Define methods that NEAR will expose as smart contract methods:

    * You are free to define any methods for the struct but only public methods will be exposed as smart contract methods;

    * Methods need to use either `&self`, `&mut self`, or `self`;

    * Decorate the `impl` section with `#[near]` macro. That is where all the M.A.G.I.C. (Macros-Auto-Generated Injected Code) happens;

    * If you need to use blockchain interface, e.g. to get the current account id then you can access it with `env::*`;



    Here is an example of smart contract methods:

    ```rust

    #[near]

    impl MyContract {

        pub fn insert_data(&mut self, key: u64, value: u64) -> Option {

            self.data.insert(key)

        }

        pub fn get_data(&self, key: u64) -> Option {

            self.data.get(&key).cloned()

        }

    }

    ```



## Building Rust Contract



### [cargo-near](https://github.com/near/cargo-near)



`cargo-near` is an easy and recommended way to build and deploy Rust contracts.



#### Installation



  Install prebuilt binaries via shell script (Linux, macOS)



```sh

curl --proto '=https' --tlsv1.2 -LsSf https://github.com/near/cargo-near/releases/latest/download/cargo-near-installer.sh | sh

```



  Install prebuilt binaries via powershell script (Windows)



```sh

irm https://github.com/near/cargo-near/releases/latest/download/cargo-near-installer.ps1 | iex

```



  Install prebuilt binaries into your Node.js application



```sh

npm install cargo-near

```



  Compile and install from source code (Cargo)



```sh

cargo install cargo-near

```



or, install the most recent version from git repository:



```sh

$ git clone https://github.com/near/cargo-near

$ cargo install --path cargo-near

```



#### Usage



See `cargo near --help` for a complete list of available commands or run `cargo near` to dive into interactive mode.

Help is also available for each individual command with a `--help` flag, e.g. `cargo near build --help`.



```sh

cargo near

```



Starts interactive mode that will allow to explore all the available commands.



```sh

cargo near build

```



Builds a NEAR smart contract along with its [ABI](https://github.com/near/abi) (while in the directory containing contract's Cargo.toml).



```sh

cargo near create-dev-account

```



Guides you through creation of a new NEAR account on [testnet](https://explorer.testnet.near.org).



```sh

cargo near deploy

```



Builds the smart contract (equivalent to `cargo near build`) and guides you to deploy it to the blockchain.



### Using cargo build



```sh

RUSTFLAGS='-C link-arg=-s' cargo build --target wasm32-unknown-unknown --release

```



## Building with reproducible builds



Since WebAssembly compiler includes a bunch of debug information into the binary, the resulting binary might be

different on different machines. To be able to compile the binary in a reproducible way, we added a Dockerfile

that allows to compile the binary.



**Use [contract-builder](https://github.com/near/near-sdk-rs/tree/master/contract-builder)**



## NEAR contract standards



[`near-contract-standards` crate](https://github.com/near/near-sdk-rs/tree/master/near-contract-standards) provides a set of interfaces and implementations for NEAR's contract standards:



- Upgradability

- Fungible Token (NEP-141). See [example usage](https://github.com/near/near-sdk-rs/tree/master/examples/fungible-token)

- Non-Fungible Token (NEP-171). See [example usage](https://github.com/near/near-sdk-rs/tree/master/examples/non-fungible-token)



## Versioning



### Semantic Versioning



This crate follows [Cargo's semver guidelines](https://doc.rust-lang.org/cargo/reference/semver.html).



State breaking changes (low-level serialization format of any data type) will be avoided at all costs. If a change like this were to happen, it would come with a major version and come with a compiler error. If you encounter one that does not, [open an issue](https://github.com/near/near-sdk-rs/issues/new)!



### MSRV



The minimum supported Rust version is currently `1.76`. There are no guarantees that this will be upheld if a security patch release needs to come in that requires a Rust toolchain increase.



## Contributing



If you are interested in contributing, please look at the [contributing guidelines](https://github.com/near/near-sdk-rs/blob/master/CONTRIBUTING.md).