Complex Cross Contract Call

Batching, parallel actions, and callback handling.

This example presents 3 instances of complex cross-contract calls on the NEAR blockchain, showcasing how to batch multiple function calls to a same contract, call multiple contracts in parallel, and handle responses in the callback. It includes both the smart contract and the frontend components.

Simple Cross-Contract Calls

Check the tutorial on how to use simple cross-contract calls

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Obtaining the Cross Contract Call Example

You have two options to start the Donation Example:

1. You can use the app through Github Codespaces, which will open a web-based interactive environment.
2. Clone the repository locally and use it from your computer.

Codespaces	Clone locally
	🌐 https://github.com/near-examples/cross-contract-calls

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Structure of the Example

The smart contract is available in two flavors: Rust and JavaScript

🌐 JavaScript

┌── sandbox-ts # sandbox testing
│    ├── external-contracts
│    │    ├── counter.wasm
│    │    ├── guest-book.wasm
│    │    └── hello-near.wasm
│    └── main.ava.ts
├── src # contract's code
│    ├── internal
│    │    ├── batch_actions.ts
│    │    ├── constants.ts
│    │    ├── multiple_contracts.ts
│    │    ├── similar_contracts.ts
│    │    └── utils.ts
│    └── contract.ts
├── package.json
├── README.md
└── tsconfig.json

🦀 Rust

┌── tests # sandbox testing
│    ├── external-contracts
│    │    ├── counter.wasm
│    │    ├── guest-book.wasm
│    │    └── hello-near.wasm
│    └── main.ava.ts
├── src # contract's code
│    ├── batch_actions.rs
│    ├── lib.rs
│    ├── multiple_contracts.rs
│    └── similar_contracts.rs
├── Cargo.toml # package manager
├── README.md
└── rust-toolchain.toml

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Smart Contract

Batch Actions

You can aggregate multiple actions directed towards one same contract into a batched transaction. Methods called this way are executed sequentially, with the added benefit that, if one fails then they all get reverted.

Getting the Last Response

In this case, the callback has access to the value returned by the last action from the chain.

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Calling Multiple Contracts

A contract can call multiple other contracts. This creates multiple transactions that execute all in parallel. If one of them fails the rest ARE NOT REVERTED.

Getting All Responses

In this case, the callback has access to an array of responses, which have either the value returned by each call, or an error message.

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Multiple Calls - Same Result Type

This example is a particular case of the previous one (Calling Multiple Contracts). It simply showcases a different way to check the results by directly accessing the promise_result array.

In this case, we call multiple contracts that will return the same type:

Getting All Responses

In this case, the callback again has access to an array of responses, which we can iterate checking the results.

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Testing the Contract

The contract readily includes a set of unit and sandbox testing to validate its functionality. To execute the tests, run the following commands:

🌐 JavaScript

cd contract-advanced-ts
yarn
yarn test

🦀 Rust

cd contract-advanced-rs
cargo test

The integration tests use a sandbox to create NEAR users and simulate interactions with the contract.

Deploying the Contract to the NEAR network

In order to deploy the contract you will need to create a NEAR account.

Short

# Create a new account pre-funded by a faucet
near create-account <accountId> --useFaucet

Full

# Create a new account pre-funded by a faucet
near account create-account sponsor-by-faucet-service <my-new-dev-account>.testnet autogenerate-new-keypair save-to-keychain network-config testnet create

Go into the directory containing the smart contract (cd contract-advanced-ts or cd contract-advanced-rs), build and deploy it:

🌐 JavaScript

npm run build
near deploy <accountId> ./build/cross_contract.wasm --initFunction new --initArgs '{"hello_account":"hello.near-example.testnet","guestbook_account":"guestbook_account.near-example.testnet","counter_account":"counter_account.near-example.testnet"}'

🦀 Rust

cargo near deploy build-non-reproducible-wasm <accountId> with-init-call new json-args '{"hello_account":"hello.near-example.testnet","guestbook_account":"guestbook_account.near-example.testnet","counter_account":"counter_account.near-example.testnet"}' prepaid-gas '100.0 Tgas' attached-deposit '0 NEAR' network-config testnet sign-with-keychain send

CLI: Interacting with the Contract

To interact with the contract through the console, you can use the following commands:

Short

# Execute contracts sequentially
# Replace <accountId> with your account ID
near call <accountId> batch_actions --useAccount <accountId> --gas 300000000000000   

# Execute contracts in parallel
# Replace <accountId> with your account ID
near call <accountId>  multiple_contracts --useAccount <accountId> --gas 300000000000000   

# Execute multiple instances of the same contract in parallel
# Replace <accountId> with your account ID
near call <accountId> similar_contracts --useAccount <accountId> --gas 300000000000000

Full

# Execute contracts sequentially
# Replace <accountId> with your account ID
near contract call-function as-transaction <accountId> batch_actions json-args '{}' prepaid-gas '300.0 Tgas' attached-deposit '0 NEAR' sign-as <accountId> network-config testnet sign-with-keychain send

# Execute contracts in parallel
# Replace <accountId> with your account ID
near contract call-function as-transaction <accountId> multiple_contracts json-args '{}' prepaid-gas '300.0 Tgas' attached-deposit '0 NEAR' sign-as <accountId> network-config testnet sign-with-keychain send

# Execute multiple instances of the same contract in parallel
# Replace <accountId> with your account ID
near contract call-function as-transaction <accountId> similar_contracts json-args '{}' prepaid-gas '300.0 Tgas' attached-deposit '0 NEAR' sign-as <accountId> network-config testnet sign-with-keychain send

If at some point you get an “Exceeded the prepaid gas” error, try to increase the gas amount used within the functions when calling other contracts

Versioning for this article

At the time of this writing, this example works with the following versions:

• near-cli: 4.0.13
• node: 18.19.1
• rustc: 1.77.0